Compiling this code with -O3:
#include <iostream>
int main(){std::cout<<"Hello World"<<std::endl;}
results in a file with a length of 25,890 bytes. (Compiled with GCC 4.8.1)
Can't the compiler just store two calls to write(STDOUT_FILENO, ???, strlen(???));, store write's contents, store the string, and boom write it to the disk? It should result in a EXE with a length under 1,024 bytes to my estimate.
Compiling a hello world program in assembly results in 17 bytes file: https://stackoverflow.com/questions/284797/hello-world-in-less-than-17-bytes, means actual code is 5-bytes long. (The string is Hello World\0)
What that EXE stores except the actual main and the functions it calls?
NOTE: This question applies to MSVC too.
Edit:
A lot of users pointed at iostream as being the culprit, so I tested this hypothesis and compiled this program with the same parameters:
int main( ) {
}
And got 23,815 bytes, the hypothesis has been disproved.
The compiler generates by default a complete PE-conformant executable. Assuming a release build, the simple code you posted might probably include:
all the PE headers and tables needed by the loader (e.g. IAT), this also means alignment requirements have to be met
CRT library initialization code
Debugging info (you need to manually drop these off even for a release build)
In case the compiler were MSVC there would have been additional inclusions:
Manifest xml and relocation data
Results of default compiler options that favor speed over size
The link you posted does contain a very small assembly "hello world" program, but in order to properly run in a Windows environment at least the complete and valid PE structure needs to be available to the loader (setting aside all the low-level issues that might cause that code not to run at all).
Assuming the loader had already and correctly 'set up' the process where to run that code into, only at that point you could map it into a PE section and do
jmp small_hello_world_entry_point
to actually execute the code.
References: The PE format
One last notice: UPX and similar compression tools are also used to reduce filesize for executables.
C++ isn't assembly, like C it comes with a lot of infrastructure. In addition to the overheads of C - required to be compatible with the C abi - C++ also has its own variants of many things, and it also has to have all the tear-up and -down code required to provide the many guarantees of the language.
Much of these are provided by libraries, but some of it has to be in the executable itself so that a failure to load shared libraries could be handled.
Under Linux/BSD we can reverse engineer an executable with objdump -dsl. I took the following code:
int main() {}
and compiled it with:
g++ -Wall -O3 -g0 test.cpp -o test.exe
The resulting executable?
6922 bytes
Then I compiled with less cruft:
g++ -Wall -O3 -g0 test.cpp -o test.exe -nostdlib
/usr/bin/ld: warning: cannot find entry symbol _start; defaulting to 0000000000400150
Basically: main is a facade entry point for our C++ code, the program really starts at _start.
Executable size?
1454 bytes
Here's how objdump describes the two:
g++ -Wall -O3 -g0 test.cpp -o test.exe
objdump -test.exe
test.exe: file format elf64-x86-64
Contents of section .interp:
400200 2f6c6962 36342f6c 642d6c69 6e75782d /lib64/ld-linux-
400210 7838362d 36342e73 6f2e3200 x86-64.so.2.
Contents of section .note.ABI-tag:
40021c 04000000 10000000 01000000 474e5500 ............GNU.
40022c 00000000 02000000 06000000 12000000 ................
Contents of section .note.gnu.build-id:
40023c 04000000 14000000 03000000 474e5500 ............GNU.
40024c a0f55c7d 671f9eb2 93078fd3 0f52581a ..\}g........RX.
40025c 544829b2 TH).
Contents of section .hash:
400260 03000000 06000000 02000000 05000000 ................
400270 00000000 00000000 00000000 01000000 ................
400280 00000000 03000000 04000000 ............
Contents of section .dynsym:
400290 00000000 00000000 00000000 00000000 ................
4002a0 00000000 00000000 10000000 20000000 ............ ...
4002b0 00000000 00000000 00000000 00000000 ................
4002c0 1f000000 20000000 00000000 00000000 .... ...........
4002d0 00000000 00000000 8b000000 12000000 ................
4002e0 00000000 00000000 00000000 00000000 ................
4002f0 33000000 20000000 00000000 00000000 3... ...........
400300 00000000 00000000 4f000000 20000000 ........O... ...
400310 00000000 00000000 00000000 00000000 ................
Contents of section .dynstr:
400320 006c6962 73746463 2b2b2e73 6f2e3600 .libstdc++.so.6.
400330 5f5f676d 6f6e5f73 74617274 5f5f005f __gmon_start__._
400340 4a765f52 65676973 74657243 6c617373 Jv_RegisterClass
400350 6573005f 49544d5f 64657265 67697374 es._ITM_deregist
400360 6572544d 436c6f6e 65546162 6c65005f erTMCloneTable._
400370 49544d5f 72656769 73746572 544d436c ITM_registerTMCl
400380 6f6e6554 61626c65 006c6962 6d2e736f oneTable.libm.so
400390 2e36006c 69626763 635f732e 736f2e31 .6.libgcc_s.so.1
4003a0 006c6962 632e736f 2e36005f 5f6c6962 .libc.so.6.__lib
4003b0 635f7374 6172745f 6d61696e 00474c49 c_start_main.GLI
4003c0 42435f32 2e322e35 00 BC_2.2.5.
Contents of section .gnu.version:
4003ca 00000000 00000200 00000000 ............
Contents of section .gnu.version_r:
4003d8 01000100 81000000 10000000 00000000 ................
4003e8 751a6909 00000200 9d000000 00000000 u.i.............
Contents of section .rela.dyn:
4003f8 50096000 00000000 06000000 01000000 P.`.............
400408 00000000 00000000 ........
Contents of section .rela.plt:
400410 70096000 00000000 07000000 03000000 p.`.............
400420 00000000 00000000 ........
Contents of section .init:
400428 4883ec08 e85b0000 00e86a01 0000e845 H....[....j....E
400438 02000048 83c408c3 ...H....
Contents of section .plt:
400440 ff351a05 2000ff25 1c052000 0f1f4000 .5.. ..%.. ...#.
400450 ff251a05 20006800 000000e9 e0ffffff .%.. .h.........
Contents of section .text:
400460 31ed4989 d15e4889 e24883e4 f0505449 1.I..^H..H...PTI
400470 c7c0e005 400048c7 c1f00540 0048c7c7 ....#.H....#.H..
400480 d0054000 e8c7ffff fff49090 4883ec08 ..#.........H...
400490 488b05b9 04200048 85c07402 ffd04883 H.... .H..t...H.
4004a0 c408c390 90909090 90909090 90909090 ................
4004b0 90909090 90909090 90909090 90909090 ................
4004c0 b88f0960 00482d88 09600048 83f80e76 ...`.H-..`.H...v
4004d0 17b80000 00004885 c0740dbf 88096000 ......H..t....`.
4004e0 ffe0660f 1f440000 f3c3660f 1f440000 ..f..D....f..D..
4004f0 be880960 004881ee 88096000 48c1fe03 ...`.H....`.H...
400500 4889f048 c1e83f48 01c648d1 fe7411b8 H..H..?H..H..t..
400510 00000000 4885c074 07bf8809 6000ffe0 ....H..t....`...
400520 f3c36666 6666662e 0f1f8400 00000000 ..fffff.........
400530 803d5104 20000075 5f5553bb 80076000 .=Q. ..u_US...`.
400540 4881eb78 07600048 83ec0848 8b053e04 H..x.`.H...H..>.
400550 200048c1 fb034883 eb01488d 6c241048 .H...H...H.l$.H
400560 39d87322 0f1f4000 4883c001 4889051d 9.s"..#.H...H...
400570 042000ff 14c57807 6000488b 050f0420 . ....x.`.H....
400580 004839d8 72e2e835 ffffffc6 05f60320 .H9.r..5.......
400590 00014883 c4085b5d f3c3660f 1f440000 ..H...[]..f..D..
4005a0 bf880760 0048833f 007505e9 40ffffff ...`.H.?.u..#...
4005b0 b8000000 004885c0 74f15548 89e5ffd0 .....H..t.UH....
4005c0 5de92aff ffff9090 90909090 90909090 ].*.............
4005d0 31c0c390 90909090 90909090 90909090 1...............
4005e0 f3c36666 6666662e 0f1f8400 00000000 ..fffff.........
4005f0 48896c24 d84c8964 24e0488d 2d630120 H.l$.L.d$.H.-c.
400600 004c8d25 5c012000 4c896c24 e84c8974 .L.%\. .L.l$.L.t
400610 24f04c89 7c24f848 895c24d0 4883ec38 $.L.|$.H.\$.H..8
400620 4c29e541 89fd4989 f648c1fd 034989d7 L).A..I..H...I..
400630 e8f3fdff ff4885ed 741c31db 0f1f4000 .....H..t.1...#.
400640 4c89fa4c 89f64489 ef41ff14 dc4883c3 L..L..D..A...H..
400650 014839eb 72ea488b 5c240848 8b6c2410 .H9.r.H.\$.H.l$.
400660 4c8b6424 184c8b6c 24204c8b 7424284c L.d$.L.l$ L.t$(L
400670 8b7c2430 4883c438 c3909090 90909090 .|$0H..8........
400680 554889e5 53bb6807 60004883 ec08488b UH..S.h.`.H...H.
400690 05d30020 004883f8 ff74140f 1f440000 ... .H...t...D..
4006a0 4883eb08 ffd0488b 034883f8 ff75f148 H.....H..H...u.H
4006b0 83c4085b 5dc39090 ...[]...
Contents of section .fini:
4006b8 4883ec08 e86ffeff ff4883c4 08c3 H....o...H....
Contents of section .rodata:
4006c8 01000200 ....
Contents of section .eh_frame_hdr:
4006cc 011b033b 20000000 03000000 04ffffff ...; ...........
4006dc 3c000000 14ffffff 54000000 24ffffff <.......T...$...
4006ec 6c000000 l...
Contents of section .eh_frame:
4006f0 14000000 00000000 017a5200 01781001 .........zR..x..
400700 1b0c0708 90010000 14000000 1c000000 ................
400710 c0feffff 03000000 00000000 00000000 ................
400720 14000000 34000000 b8feffff 02000000 ....4...........
400730 00000000 00000000 24000000 4c000000 ........$...L...
400740 b0feffff 89000000 00518c05 86065f0e .........Q...._.
400750 4083078f 028e038d 0402580e 08000000 #.........X.....
400760 00000000 ....
Contents of section .ctors:
600768 ffffffff ffffffff 00000000 00000000 ................
Contents of section .dtors:
600778 ffffffff ffffffff 00000000 00000000 ................
Contents of section .jcr:
600788 00000000 00000000 ........
Contents of section .dynamic:
600790 01000000 00000000 01000000 00000000 ................
6007a0 01000000 00000000 69000000 00000000 ........i.......
6007b0 01000000 00000000 73000000 00000000 ........s.......
6007c0 01000000 00000000 81000000 00000000 ................
6007d0 0c000000 00000000 28044000 00000000 ........(.#.....
6007e0 0d000000 00000000 b8064000 00000000 ..........#.....
6007f0 04000000 00000000 60024000 00000000 ........`.#.....
600800 05000000 00000000 20034000 00000000 ........ .#.....
600810 06000000 00000000 90024000 00000000 ..........#.....
600820 0a000000 00000000 a9000000 00000000 ................
600830 0b000000 00000000 18000000 00000000 ................
600840 15000000 00000000 00000000 00000000 ................
600850 03000000 00000000 58096000 00000000 ........X.`.....
600860 02000000 00000000 18000000 00000000 ................
600870 14000000 00000000 07000000 00000000 ................
600880 17000000 00000000 10044000 00000000 ..........#.....
600890 07000000 00000000 f8034000 00000000 ..........#.....
6008a0 08000000 00000000 18000000 00000000 ................
6008b0 09000000 00000000 18000000 00000000 ................
6008c0 feffff6f 00000000 d8034000 00000000 ...o......#.....
6008d0 ffffff6f 00000000 01000000 00000000 ...o............
6008e0 f0ffff6f 00000000 ca034000 00000000 ...o......#.....
6008f0 00000000 00000000 00000000 00000000 ................
600900 00000000 00000000 00000000 00000000 ................
600910 00000000 00000000 00000000 00000000 ................
600920 00000000 00000000 00000000 00000000 ................
600930 00000000 00000000 00000000 00000000 ................
600940 00000000 00000000 00000000 00000000 ................
Contents of section .got:
600950 00000000 00000000 ........
Contents of section .got.plt:
600958 90076000 00000000 00000000 00000000 ..`.............
600968 00000000 00000000 56044000 00000000 ........V.#.....
Contents of section .data:
600978 00000000 00000000 00000000 00000000 ................
Contents of section .comment:
0000 4743433a 2028474e 55292034 2e342e37 GCC: (GNU) 4.4.7
0010 20323031 32303331 33202852 65642048 20120313 (Red H
0020 61742034 2e342e37 2d313129 00474343 at 4.4.7-11).GCC
0030 3a202847 4e552920 342e392e 782d676f : (GNU) 4.9.x-go
0040 6f676c65 20323031 35303132 33202870 ogle 20150123 (p
0050 72657265 6c656173 652900 rerelease).
Disassembly of section .init:
0000000000400428 <_init>:
_init():
400428: 48 83 ec 08 sub $0x8,%rsp
40042c: e8 5b 00 00 00 callq 40048c <call_gmon_start>
400431: e8 6a 01 00 00 callq 4005a0 <frame_dummy>
400436: e8 45 02 00 00 callq 400680 <__do_global_ctors_aux>
40043b: 48 83 c4 08 add $0x8,%rsp
40043f: c3 retq
Disassembly of section .plt:
0000000000400440 <__libc_start_main#plt-0x10>:
400440: ff 35 1a 05 20 00 pushq 0x20051a(%rip) # 600960 <_GLOBAL_OFFSET_TABLE_+0x8>
400446: ff 25 1c 05 20 00 jmpq *0x20051c(%rip) # 600968 <_GLOBAL_OFFSET_TABLE_+0x10>
40044c: 0f 1f 40 00 nopl 0x0(%rax)
0000000000400450 <__libc_start_main#plt>:
400450: ff 25 1a 05 20 00 jmpq *0x20051a(%rip) # 600970 <_GLOBAL_OFFSET_TABLE_+0x18>
400456: 68 00 00 00 00 pushq $0x0
40045b: e9 e0 ff ff ff jmpq 400440 <_init+0x18>
Disassembly of section .text:
0000000000400460 <_start>:
_start():
400460: 31 ed xor %ebp,%ebp
400462: 49 89 d1 mov %rdx,%r9
400465: 5e pop %rsi
400466: 48 89 e2 mov %rsp,%rdx
400469: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
40046d: 50 push %rax
40046e: 54 push %rsp
40046f: 49 c7 c0 e0 05 40 00 mov $0x4005e0,%r8
400476: 48 c7 c1 f0 05 40 00 mov $0x4005f0,%rcx
40047d: 48 c7 c7 d0 05 40 00 mov $0x4005d0,%rdi
400484: e8 c7 ff ff ff callq 400450 <__libc_start_main#plt>
400489: f4 hlt
40048a: 90 nop
40048b: 90 nop
000000000040048c <call_gmon_start>:
call_gmon_start():
40048c: 48 83 ec 08 sub $0x8,%rsp
400490: 48 8b 05 b9 04 20 00 mov 0x2004b9(%rip),%rax # 600950 <_DYNAMIC+0x1c0>
400497: 48 85 c0 test %rax,%rax
40049a: 74 02 je 40049e <call_gmon_start+0x12>
40049c: ff d0 callq *%rax
40049e: 48 83 c4 08 add $0x8,%rsp
4004a2: c3 retq
4004a3: 90 nop
4004a4: 90 nop
4004a5: 90 nop
4004a6: 90 nop
4004a7: 90 nop
4004a8: 90 nop
4004a9: 90 nop
4004aa: 90 nop
4004ab: 90 nop
4004ac: 90 nop
4004ad: 90 nop
4004ae: 90 nop
4004af: 90 nop
4004b0: 90 nop
4004b1: 90 nop
4004b2: 90 nop
4004b3: 90 nop
4004b4: 90 nop
4004b5: 90 nop
4004b6: 90 nop
4004b7: 90 nop
4004b8: 90 nop
4004b9: 90 nop
4004ba: 90 nop
4004bb: 90 nop
4004bc: 90 nop
4004bd: 90 nop
4004be: 90 nop
4004bf: 90 nop
00000000004004c0 <deregister_tm_clones>:
deregister_tm_clones():
4004c0: b8 8f 09 60 00 mov $0x60098f,%eax
4004c5: 48 2d 88 09 60 00 sub $0x600988,%rax
4004cb: 48 83 f8 0e cmp $0xe,%rax
4004cf: 76 17 jbe 4004e8 <deregister_tm_clones+0x28>
4004d1: b8 00 00 00 00 mov $0x0,%eax
4004d6: 48 85 c0 test %rax,%rax
4004d9: 74 0d je 4004e8 <deregister_tm_clones+0x28>
4004db: bf 88 09 60 00 mov $0x600988,%edi
4004e0: ff e0 jmpq *%rax
4004e2: 66 0f 1f 44 00 00 nopw 0x0(%rax,%rax,1)
4004e8: f3 c3 repz retq
4004ea: 66 0f 1f 44 00 00 nopw 0x0(%rax,%rax,1)
00000000004004f0 <register_tm_clones>:
register_tm_clones():
4004f0: be 88 09 60 00 mov $0x600988,%esi
4004f5: 48 81 ee 88 09 60 00 sub $0x600988,%rsi
4004fc: 48 c1 fe 03 sar $0x3,%rsi
400500: 48 89 f0 mov %rsi,%rax
400503: 48 c1 e8 3f shr $0x3f,%rax
400507: 48 01 c6 add %rax,%rsi
40050a: 48 d1 fe sar %rsi
40050d: 74 11 je 400520 <register_tm_clones+0x30>
40050f: b8 00 00 00 00 mov $0x0,%eax
400514: 48 85 c0 test %rax,%rax
400517: 74 07 je 400520 <register_tm_clones+0x30>
400519: bf 88 09 60 00 mov $0x600988,%edi
40051e: ff e0 jmpq *%rax
400520: f3 c3 repz retq
400522: 66 66 66 66 66 2e 0f data32 data32 data32 data32 nopw %cs:0x0(%rax,%rax,1)
400529: 1f 84 00 00 00 00 00
0000000000400530 <__do_global_dtors_aux>:
__do_global_dtors_aux():
400530: 80 3d 51 04 20 00 00 cmpb $0x0,0x200451(%rip) # 600988 <__bss_start>
400537: 75 5f jne 400598 <__do_global_dtors_aux+0x68>
400539: 55 push %rbp
40053a: 53 push %rbx
40053b: bb 80 07 60 00 mov $0x600780,%ebx
400540: 48 81 eb 78 07 60 00 sub $0x600778,%rbx
400547: 48 83 ec 08 sub $0x8,%rsp
40054b: 48 8b 05 3e 04 20 00 mov 0x20043e(%rip),%rax # 600990 <dtor_idx.6648>
400552: 48 c1 fb 03 sar $0x3,%rbx
400556: 48 83 eb 01 sub $0x1,%rbx
40055a: 48 8d 6c 24 10 lea 0x10(%rsp),%rbp
40055f: 48 39 d8 cmp %rbx,%rax
400562: 73 22 jae 400586 <__do_global_dtors_aux+0x56>
400564: 0f 1f 40 00 nopl 0x0(%rax)
400568: 48 83 c0 01 add $0x1,%rax
40056c: 48 89 05 1d 04 20 00 mov %rax,0x20041d(%rip) # 600990 <dtor_idx.6648>
400573: ff 14 c5 78 07 60 00 callq *0x600778(,%rax,8)
40057a: 48 8b 05 0f 04 20 00 mov 0x20040f(%rip),%rax # 600990 <dtor_idx.6648>
400581: 48 39 d8 cmp %rbx,%rax
400584: 72 e2 jb 400568 <__do_global_dtors_aux+0x38>
400586: e8 35 ff ff ff callq 4004c0 <deregister_tm_clones>
40058b: c6 05 f6 03 20 00 01 movb $0x1,0x2003f6(%rip) # 600988 <__bss_start>
400592: 48 83 c4 08 add $0x8,%rsp
400596: 5b pop %rbx
400597: 5d pop %rbp
400598: f3 c3 repz retq
40059a: 66 0f 1f 44 00 00 nopw 0x0(%rax,%rax,1)
00000000004005a0 <frame_dummy>:
frame_dummy():
4005a0: bf 88 07 60 00 mov $0x600788,%edi
4005a5: 48 83 3f 00 cmpq $0x0,(%rdi)
4005a9: 75 05 jne 4005b0 <frame_dummy+0x10>
4005ab: e9 40 ff ff ff jmpq 4004f0 <register_tm_clones>
4005b0: b8 00 00 00 00 mov $0x0,%eax
4005b5: 48 85 c0 test %rax,%rax
4005b8: 74 f1 je 4005ab <frame_dummy+0xb>
4005ba: 55 push %rbp
4005bb: 48 89 e5 mov %rsp,%rbp
4005be: ff d0 callq *%rax
4005c0: 5d pop %rbp
4005c1: e9 2a ff ff ff jmpq 4004f0 <register_tm_clones>
4005c6: 90 nop
4005c7: 90 nop
4005c8: 90 nop
4005c9: 90 nop
4005ca: 90 nop
4005cb: 90 nop
4005cc: 90 nop
4005cd: 90 nop
4005ce: 90 nop
4005cf: 90 nop
00000000004005d0 <main>:
main():
4005d0: 31 c0 xor %eax,%eax
4005d2: c3 retq
4005d3: 90 nop
4005d4: 90 nop
4005d5: 90 nop
4005d6: 90 nop
4005d7: 90 nop
4005d8: 90 nop
4005d9: 90 nop
4005da: 90 nop
4005db: 90 nop
4005dc: 90 nop
4005dd: 90 nop
4005de: 90 nop
4005df: 90 nop
00000000004005e0 <__libc_csu_fini>:
__libc_csu_fini():
4005e0: f3 c3 repz retq
4005e2: 66 66 66 66 66 2e 0f data32 data32 data32 data32 nopw %cs:0x0(%rax,%rax,1)
4005e9: 1f 84 00 00 00 00 00
00000000004005f0 <__libc_csu_init>:
__libc_csu_init():
4005f0: 48 89 6c 24 d8 mov %rbp,-0x28(%rsp)
4005f5: 4c 89 64 24 e0 mov %r12,-0x20(%rsp)
4005fa: 48 8d 2d 63 01 20 00 lea 0x200163(%rip),%rbp # 600764 <__init_array_end>
400601: 4c 8d 25 5c 01 20 00 lea 0x20015c(%rip),%r12 # 600764 <__init_array_end>
400608: 4c 89 6c 24 e8 mov %r13,-0x18(%rsp)
40060d: 4c 89 74 24 f0 mov %r14,-0x10(%rsp)
400612: 4c 89 7c 24 f8 mov %r15,-0x8(%rsp)
400617: 48 89 5c 24 d0 mov %rbx,-0x30(%rsp)
40061c: 48 83 ec 38 sub $0x38,%rsp
400620: 4c 29 e5 sub %r12,%rbp
400623: 41 89 fd mov %edi,%r13d
400626: 49 89 f6 mov %rsi,%r14
400629: 48 c1 fd 03 sar $0x3,%rbp
40062d: 49 89 d7 mov %rdx,%r15
400630: e8 f3 fd ff ff callq 400428 <_init>
400635: 48 85 ed test %rbp,%rbp
400638: 74 1c je 400656 <__libc_csu_init+0x66>
40063a: 31 db xor %ebx,%ebx
40063c: 0f 1f 40 00 nopl 0x0(%rax)
400640: 4c 89 fa mov %r15,%rdx
400643: 4c 89 f6 mov %r14,%rsi
400646: 44 89 ef mov %r13d,%edi
400649: 41 ff 14 dc callq *(%r12,%rbx,8)
40064d: 48 83 c3 01 add $0x1,%rbx
400651: 48 39 eb cmp %rbp,%rbx
400654: 72 ea jb 400640 <__libc_csu_init+0x50>
400656: 48 8b 5c 24 08 mov 0x8(%rsp),%rbx
40065b: 48 8b 6c 24 10 mov 0x10(%rsp),%rbp
400660: 4c 8b 64 24 18 mov 0x18(%rsp),%r12
400665: 4c 8b 6c 24 20 mov 0x20(%rsp),%r13
40066a: 4c 8b 74 24 28 mov 0x28(%rsp),%r14
40066f: 4c 8b 7c 24 30 mov 0x30(%rsp),%r15
400674: 48 83 c4 38 add $0x38,%rsp
400678: c3 retq
400679: 90 nop
40067a: 90 nop
40067b: 90 nop
40067c: 90 nop
40067d: 90 nop
40067e: 90 nop
40067f: 90 nop
0000000000400680 <__do_global_ctors_aux>:
__do_global_ctors_aux():
400680: 55 push %rbp
400681: 48 89 e5 mov %rsp,%rbp
400684: 53 push %rbx
400685: bb 68 07 60 00 mov $0x600768,%ebx
40068a: 48 83 ec 08 sub $0x8,%rsp
40068e: 48 8b 05 d3 00 20 00 mov 0x2000d3(%rip),%rax # 600768 <__CTOR_LIST__>
400695: 48 83 f8 ff cmp $0xffffffffffffffff,%rax
400699: 74 14 je 4006af <__do_global_ctors_aux+0x2f>
40069b: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
4006a0: 48 83 eb 08 sub $0x8,%rbx
4006a4: ff d0 callq *%rax
4006a6: 48 8b 03 mov (%rbx),%rax
4006a9: 48 83 f8 ff cmp $0xffffffffffffffff,%rax
4006ad: 75 f1 jne 4006a0 <__do_global_ctors_aux+0x20>
4006af: 48 83 c4 08 add $0x8,%rsp
4006b3: 5b pop %rbx
4006b4: 5d pop %rbp
4006b5: c3 retq
4006b6: 90 nop
4006b7: 90 nop
Disassembly of section .fini:
00000000004006b8 <_fini>:
_fini():
4006b8: 48 83 ec 08 sub $0x8,%rsp
4006bc: e8 6f fe ff ff callq 400530 <__do_global_dtors_aux>
4006c1: 48 83 c4 08 add $0x8,%rsp
4006c5: c3 retq
and the smaller file:
g++ -Wall -O3 -g0 test.cpp -o test.exe -nostdlib
/usr/bin/ld: warning: cannot find entry symbol _start; defaulting to 0000000000400150
test.exe: file format elf64-x86-64
Contents of section .note.gnu.build-id:
400120 04000000 14000000 03000000 474e5500 ............GNU.
400130 d4b1e35c 21d1f541 b81d3ac9 d62bac7a ...\!..A..:..+.z
400140 606b1ad4 `k..
Contents of section .text:
400150 31c0c3 1..
Contents of section .eh_frame_hdr:
400154 011b033b 10000000 01000000 fcffffff ...;............
400164 2c000000 ,...
Contents of section .eh_frame:
400168 14000000 00000000 017a5200 01781001 .........zR..x..
400178 1b0c0708 90010000 14000000 1c000000 ................
400188 c8ffffff 03000000 00000000 00000000 ................
Contents of section .comment:
0000 4743433a 2028474e 55292034 2e392e78 GCC: (GNU) 4.9.x
0010 2d676f6f 676c6520 32303135 30313233 -google 20150123
0020 20287072 6572656c 65617365 2900 (prerelease).
Disassembly of section .text:
0000000000400150 <main>:
main():
400150: 31 c0 xor %eax,%eax
400152: c3 retq
It's worth noting that this executable doesn't work, it segfaults: to make it work, we'd actually have to implement _start instead of main.
We can see here that the bulk of the larger executable is glue code that deals with loading the dynamic library and preparing the broader environment required by the standard library.
--- EDIT ---
Even our smaller code still has to include exception handling, ctor/dtor support for globals, and so forth. It could probably elide such things and if you dig deeply enough you can probably find ways to elide them, but in general you probably don't need to, and it is probably easier to always include such basic support than to have the majority of new programmers stumbling over "how do I force the compiler to emit basic language support" than have a handful of new embedded programmers asking "how can I prevent the compiler emitting basic language support?".
Note also that the compiler generates ELF format binaries, this is a small contribution (maybe ~60bytes), plus emitting it's own identity added some size. But the bulk of the smaller binary is language support (EH and CTOR/DTOR).
Compiling with #include <iostream> and -O3 -g0 produces a 7625 byte binary, if I compile that with -O0 -g3 it produces a 64Kb binary most of which is text describing symbols from the STL.
Your executable is including the C runtime, which knows how to do things like get the environment, setup the argv vector, and close all open files after calling exit() but before calling _exit().
There are many things which could affect the final file size during compilation, as other posters have pointed out.
Dissecting your specific example is more work than I'm willing to put in, but I know of a similar example from many years ago that should help you to understand the general problem, and guide you towards finding the specific answer you seek.
http://www.muppetlabs.com/~breadbox/software/tiny/teensy.html
This is done in C (rather than C++) using GCC, looking at the size of the ELF executable (not a Windows EXE), but as I said many of the same problems apply. In this case, the author looks at just return 42;
After you've read that document, consider that printing to stdout is considerably more complex than just returning a number. Also, since you are using C++ and cout <<, there's a lot of code hiding in there that you didn't write, and you can't really know how it's implemented without looking at that source.
people keep ignoring/forgetting that executables created in high level languages need engine to run properly. for example C++ engine is responsible for things like:
heap/stack management
when you call new,delete you are not actually accessing OS functions
instead the engine use its own allocated heap memory
so engine has it own memory management that takes code/space
local variables memory management
each time you call any function all the local variables must be allocated
and released before exiting it
classes/templates
to handle these properly you need quite a lot of code
In addition to this you have to link all the stuff you use like:
RTL most executables nowdays MSVCPP and MSVB does not link them so we need to install huge amount of RTLs in system to make exe to even run. but still the linking to used DLL's must be present in executable (see DLL linking on runtime)
debug info
frameworks linkage (similar to RTL you need the code to bind to frameworks libs too)
for high level winows/forms IDE's you also have the window engine present
included libs and linked objs (iostream classes and operators even if you use just << you need much more of them to make it work...)
You can look at the C++ engine as a small operating system within operating system
in standalone MCU apps they are really the OS itself
Another space is occupied by the executable format (like PE), and also code aligns add some space
When you put all these together then the 26KB is not so insane anymore
Compilers are not omnipotent.
std::cout is a stream object, with a set of data members for managing a buffer (allocating it, copying data to it and, when the stream is destroyed, releasing it).
The operator<< is implemented as an overloaded function which interprets its arguments and - when supplied a string - copies data to the buffer, with some logic that potentially flushes the buffer when it is full.
std::endl is actually an function which - in cooperation with all versions of a stream's operator<<() - affects data owned by the stream. Specifically, it inserts a newline into the streams buffer, and then flushes the buffer.
Flushing the stream's buffer calls other functions that copy data from the buffer to the standard output device (say, the screen).
All of the above is what the statement std::cout<<"Hello World"<<std::endl does.
In addition, as a C++ program, there is a certain amount of code that must be executed before main() is even called. This includes checking if the program was run with command line arguments, creating streams like std::cout, std::cerr, std::cin (there are others) ensuring those streams are connected with relevant devices (like the terminal, or pipes, or whatever). When main() returns, it is then necessary to release all the streams created (and flush their buffers), and things like that.
All of the above involves invoking other functionality. Creating a buffer for the stream means that buffer must be allocated and - after main() returns - released.
The specification of C++ streams also involves error checking. The allocation of std::cout's buffer might fail (e.g. if the host system doesn't have much free memory). The standard output device might be redirected to a file, which has limited capacity - so writing data to it might fail. All of those things must be checked for and handled gracefully.
All of this stuff will be in this 26K executable (unless that code is in runtime libraries).
In principle, the compiler can recognise that the program is not using its command line arguments (so not include code to manage command line arguments), is only writing to std::cout (so no need to create all the other streams before main() and release them after main() returns), is only using two overloaded versions of operator<<() and one stream manipulator (so the linker need not include code for all other member functions of the stream). It might also recognise that the statement writes data to the stream and immediately flushes the buffer - and thereby eliminate std::cout's buffer and all code that manages it. If the compiler can read the programmer's mind (few compilers can, in practice) it might work out that none of the buffers are actually needed, that the user will never run the program with standard output redirected, etc - and eliminate the code and data structures associated with all those things.
So, how would a compiler recognise that all those things aren't needed? Compilers are software, so they have to conduct some level of analysis on their inputs (e.g. source files). The analysis to eliminate all the code that a human might deem unnecessary is significant - so would take time. If the compiler doesn't do the analysis, potentially the linker might. Whether that analysis to eliminate unnecessary code is done by the compiler or linker is irrelevant - it takes time. Potentially significant time.
Programmers tend to be impatient. Very few programmers would tolerate a build process for a simple "hello world" program that took more than a few seconds (maybe they will tolerate a minute, but not much more).
That leaves compiler vendors with a decision. They can get their programmers to design and implement all sorts of analysis to eliminate unwanted code. That will add weeks - or, if they are working to a tight deadline, months - to implement, validate, verify, and ship a working compiler to customers (other developers). That compiler will be painfully slow at compiling code. Instead, vendors (and their developers) choose to implement less of that analysis in their compiler, so they can actually ship a working compiler to developers who will use it within a reasonable time. This compiler will produce an executable in a time that is somewhat tolerable for most programmers (say, under a minute for a "hello world" program). So what if the executable is larger? It will work. Hardware (e.g. drives) is relatively inexpensive and developer effort is relatively expensive.
It's very old question. It have clear answer. The most problem is that one have to write many small pieces of information and make many small test which demonstrates different aspects of PE structures. I try to skip details and to describe the main parts of the problem based on Microsoft Visual Studio, which I know and use since many years. All other compilers do mostly the same, and I suppose that one need use just a little other options of compiler and linker.
First of all I suggest you to set breakpoint on the first line of the main, start debugging and to examine the Call Stack windows of the debugger. You will see something like
So the first thing, which is very important to understand, the main is not the first function which will be called in your program. The entry point of the program is mainCRTStartup, which calls __tmainCRTStartup, which calls main.
The CRT Startup code make many small things. One thing is very easy to understand: it uses GetCommandLineW Windows API to get the command line and parse the parameters, then it calls main with the parameters.
To reduce the size of the code there are two common approach:
use CRT from DLL
remove CRT from the EXE if it's not really used in the code.
It's very helpful if you start cmd.exe using "VS2013 x64 Native Tools Command Prompt" (or some close command prompt). Some additional paths will be set inside of the command prompt and you can use for example dumpbin.exe utility.
If you would use Multi-threaded DLL (/MD) compiler option then you will get 7K large exe file. "dumpbin /imports HelloWorld.exe" will show you that your program uses "MSVCR120.dll" together with "KERNEL32.dll".
Removing of CRT depends on the version of c/cpp compiler (the version of Visual Studio) which you use and even from the extension of the file: .c or .cpp. I understand your question as the common question for understanding the problem. So I suggest to start with the most simple case, rename .cpp file .c and the beginning and to modify the code to the following
#include <Windows.h>
int mainCRTStartup()
{
return 0;
}
One can see now
C:\Oleg\StackOverflow\HelloWorld\Release>dir HelloWorld.exe
Volume in drive C has no label.
Volume Serial Number is 4CF9-FADF
Directory of C:\Oleg\StackOverflow\HelloWorld\Release
21.06.2015 12:56 3.584 HelloWorld.exe
1 File(s) 3.584 bytes
0 Dir(s) 16.171.196.416 bytes free
C:\Oleg\StackOverflow\HelloWorld\Release>dumpbin HelloWorld.exe
Microsoft (R) COFF/PE Dumper Version 12.00.31101.0
Copyright (C) Microsoft Corporation. All rights reserved.
Dump of file HelloWorld.exe
File Type: EXECUTABLE IMAGE
Summary
1000 .data
1000 .rdata
1000 .reloc
1000 .rsrc
1000 .text
One can add the linker option /MERGE:.rdata=.text to reduce the size and to remove one section
C:\Oleg\StackOverflow\HelloWorld\Release>dir HelloWorld.exe
Volume in drive C has no label.
Volume Serial Number is 4CF9-FADF
Directory of C:\Oleg\StackOverflow\HelloWorld\Release
21.06.2015 18:44 3.072 HelloWorld.exe
1 File(s) 3.072 bytes
0 Dir(s) 16.170.852.352 bytes free
C:\Oleg\StackOverflow\HelloWorld\Release>dumpbin HelloWorld.exe
Microsoft (R) COFF/PE Dumper Version 12.00.31101.0
Copyright (C) Microsoft Corporation. All rights reserved.
Dump of file HelloWorld.exe
File Type: EXECUTABLE IMAGE
Summary
1000 .data
1000 .reloc
1000 .rsrc
1000 .text
To have "Hello World" program I suggest to modify the code to
#include <Windows.h>
int mainCRTStartup()
{
LPCTSTR pszString = TEXT("Hello world");
DWORD cbWritten;
WriteConsole(GetStdHandle(STD_OUTPUT_HANDLE), pszString, lstrlen(pszString), &cbWritten, NULL);
return 0;
}
One can easy verify that the code work and it's still small.
To remove CRT from .cpp file I suggest to follow the following steps. First of all we would use the following HelloWorld.cpp code
#include <Windows.h>
int mainCRTStartup()
{
LPCTSTR pszString = TEXT("Hello world");
DWORD cbWritten;
WriteConsole(GetStdHandle(STD_OUTPUT_HANDLE), pszString, lstrlen(pszString), &cbWritten, NULL);
return 0;
}
It's important that one verify some compiler and linker options and set/remove someone. I included the settings on the pictures below:
The last screen shows that we remove binding to default libraries which we don't need. The compiler uses directive like #pragma comment(lib, "some.lib") to inject usage of some libraries. By usage the options /NODEFAULTLIB we remove such libs and the exe will be compiled like we need.
One will see that the resulting HelloWorld.exe have only 3K (3.072 bytes) and there are exist dependency to one KERNEL32.dll only:
C:\Oleg\StackOverflow\HelloWorld\Release>dumpbin /imports HelloWorld.exe
Microsoft (R) COFF/PE Dumper Version 12.00.31101.0
Copyright (C) Microsoft Corporation. All rights reserved.
Dump of file HelloWorld.exe
File Type: EXECUTABLE IMAGE
Section contains the following imports:
KERNEL32.dll
402000 Import Address Table
402038 Import Name Table
0 time date stamp
0 Index of first forwarder reference
60B lstrlenW
5E0 WriteConsoleW
2C0 GetStdHandle
Summary
1000 .idata
1000 .reloc
1000 .rsrc
1000 .text
One can download the corresponding Visual Studio 2013 demo project from here. One need switch from default "Debug" compiling to "Release" and rebuild solution. One will have working HelloWorld.exe which length is 3K.
This does show how hard it can be to write a program with identical semantics.
<<std::endl will flush a stream if that stream is good(). That means the whole error handling code of ostream must be present.
Also, std::cout could have its streambuf swapped out from under it. The compiler cannot know it's actually going to STDOUT_FILENO. It has to use the whole streambuf intermediate layer.
Related
I have written the following function:
inline void putc(int c)
{
static Cons_serial serial;
if (serial.enabled())
serial.putc(c);
}
Where Cons_serial is a class with a non-trivial default constructor. I believe the exact class definition is not important here but you can correct me on that. I'm compiling for x86 32 bit with g++ using the following flags: -m32 -fno-PIC -ffreestanding -fno-rtti -fno-exceptions -fno-threadsafe-statics -O0, the generated assembly code for putc looks like this:
00100221 <_Z4putci>:
100221: 55 push %ebp
100222: 89 e5 mov %esp,%ebp
100224: 83 ec 08 sub $0x8,%esp
100227: b8 f8 02 10 00 mov $0x1002f8,%eax
10022c: 0f b6 00 movzbl (%eax),%eax
10022f: 84 c0 test %al,%al
100231: 75 18 jne 10024b <_Z4putci+0x2a>
100233: 83 ec 0c sub $0xc,%esp
100236: 68 f0 02 10 00 push $0x1002f0
10023b: e8 36 fe ff ff call 100076 <_ZN11Cons_serialC1Ev>
100240: 83 c4 10 add $0x10,%esp
100243: b8 f8 02 10 00 mov $0x1002f8,%eax
100248: c6 00 01 movb $0x1,(%eax)
10024b: 83 ec 0c sub $0xc,%esp
10024e: 68 f0 02 10 00 push $0x1002f0
100253: e8 4c fe ff ff call 1000a4 <_ZNK11Cons_serial7enabledEv>
100258: 83 c4 10 add $0x10,%esp
10025b: 84 c0 test %al,%al
10025d: 74 13 je 100272 <_Z4putci+0x51>
10025f: 83 ec 08 sub $0x8,%esp
100262: ff 75 08 pushl 0x8(%ebp)
100265: 68 f0 02 10 00 push $0x1002f0
10026a: e8 41 fe ff ff call 1000b0 <_ZN11Cons_serial4putcEi>
10026f: 83 c4 10 add $0x10,%esp
100272: 90 nop
100273: c9 leave
100274: c3 ret
During execution, the jump at 100231 is taken the first time the function runs, thus Cons_serial is never called. Why knowledge of x86 assembly is questionable, what do the instructions leading up to that one actually do? I assume the code is meant to skip the constructor call on subsequent function calls. But then why is it skipped the first time the function runs as well?
EDIT: This code is part of a kernel I'm writing and I suspect the root cause might be an issue with my kernel's .bss section, here is the linker script I use:
OUTPUT_FORMAT("elf32-i386")
ENTRY(_start)
SECTIONS
{
. = 0x100000;
.text : AT(0x100000) {
*(.text)
}
.data : SUBALIGN(2) {
*(.data);
*(.rodata*);
}
.bss : SUBALIGN(4) {
__bss_start = .;
*(.COMMON);
*(.bss*)
. = ALIGN(4);
__bss_end = .;
}
/DISCARD/ : {
*(.eh_frame)
*(.comment)
}
}
And here's the code I use to zero the .bss section:
extern uint32_t __bss_start;
extern uint32_t __bss_end;
void zero_bss()
{
for (uint32_t bss_addr = __bss_start; bss_addr < __bss_end; ++bss_addr)
*reinterpret_cast<uint8_t *>(bss_addr) = 0x00;
}
But when zero_bss runs, __bss_start is 0x27 and __bss_end is 0x101 which is not at all what I'd except (the BSS should encompass address 0x1002f8 after all).
I've solved it now, the hint from #user3124812 was what got me there, thanks again.
My zero_bss code was faulty, I needed to take the addresses of the __bss* markers from the linker script, i.e.:
extern uint8_t __bss_start;
extern uint8_t __bss_end;
void zero_bss()
{
uint8_t *bss_start = reinterpret_cast<uint8_t *>(&__bss_start);
uint8_t *bss_end = reinterpret_cast<uint8_t *>(&__bss_end);
for (uint8_t *bss_addr = bss_start; bss_addr < bss_end; ++bss_addr)
*bss_addr = 0x00;
}
Now everything works.
EDIT:
I've voted to close this is it is now incorrect.
In March 2016 Valgrind gained an option "--run-cxx-freeres=<yes|no>" (default is yes). This will call a libstdc++ function to free one-off allocations used for things like iostream. If you are using a post-2016 Valgrind and libstdc++ you will get
==9356== HEAP SUMMARY:
==9356== in use at exit: 0 bytes in 0 blocks
==9356== total heap usage: 1 allocs, 1 frees, 72,704 bytes allocated
==9356==
==9356== All heap blocks were freed -- no leaks are possible
ORIGINAL POST:
Take the following trivial program:
#include <iostream>
int main() {
return 0;
}
If I run this using valgrind, I'm told that there are 72,704 bytes in 1 blocks that are still reachable. There have been extensive discussions on SO about whether or not to worry about still reachable warnings--I'm not concerned about that. I'd just like to understand how simply including a standard library header could cause a still reachable warning, when none of the objects from that library were allocated in the program itself.
Here is the full valgrind output:
$ valgrind --leak-check=full --track-origins=yes --show-reachable=yes ./ValgrindTest
==27671== Memcheck, a memory error detector
==27671== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==27671== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==27671== Command: ./ValgrindTest
==27671==
==27671==
==27671== HEAP SUMMARY:
==27671== in use at exit: 72,704 bytes in 1 blocks
==27671== total heap usage: 1 allocs, 0 frees, 72,704 bytes allocated
==27671==
==27671== 72,704 bytes in 1 blocks are still reachable in loss record 1 of 1
==27671== at 0x4C2AB9D: malloc (vg_replace_malloc.c:296)
==27671== by 0x4EC060F: ??? (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21)
==27671== by 0x400F305: call_init.part.0 (dl-init.c:85)
==27671== by 0x400F3DE: call_init (dl-init.c:52)
==27671== by 0x400F3DE: _dl_init (dl-init.c:134)
==27671== by 0x40016E9: ??? (in /lib/x86_64-linux-gnu/ld-2.15.so)
==27671==
==27671== LEAK SUMMARY:
==27671== definitely lost: 0 bytes in 0 blocks
==27671== indirectly lost: 0 bytes in 0 blocks
==27671== possibly lost: 0 bytes in 0 blocks
==27671== still reachable: 72,704 bytes in 1 blocks
==27671== suppressed: 0 bytes in 0 blocks
==27671==
==27671== For counts of detected and suppressed errors, rerun with: -v
==27671== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
And an object dump:
$ objdump -d ValgrindTest
ValgrindTest: file format elf64-x86-64
Disassembly of section .init:
0000000000400718 <_init>:
400718: 48 83 ec 08 sub $0x8,%rsp
40071c: e8 8b 00 00 00 callq 4007ac <call_gmon_start>
400721: 48 83 c4 08 add $0x8,%rsp
400725: c3 retq
Disassembly of section .plt:
0000000000400730 <_ZNSt8ios_base4InitC1Ev#plt-0x10>:
400730: ff 35 ba 08 20 00 pushq 0x2008ba(%rip) # 600ff0 <_GLOBAL_OFFSET_TABLE_+0x8>
400736: ff 25 bc 08 20 00 jmpq *0x2008bc(%rip) # 600ff8 <_GLOBAL_OFFSET_TABLE_+0x10>
40073c: 0f 1f 40 00 nopl 0x0(%rax)
0000000000400740 <_ZNSt8ios_base4InitC1Ev#plt>:
400740: ff 25 ba 08 20 00 jmpq *0x2008ba(%rip) # 601000 <_GLOBAL_OFFSET_TABLE_+0x18>
400746: 68 00 00 00 00 pushq $0x0
40074b: e9 e0 ff ff ff jmpq 400730 <_init+0x18>
0000000000400750 <__libc_start_main#plt>:
400750: ff 25 b2 08 20 00 jmpq *0x2008b2(%rip) # 601008 <_GLOBAL_OFFSET_TABLE_+0x20>
400756: 68 01 00 00 00 pushq $0x1
40075b: e9 d0 ff ff ff jmpq 400730 <_init+0x18>
0000000000400760 <__cxa_atexit#plt>:
400760: ff 25 aa 08 20 00 jmpq *0x2008aa(%rip) # 601010 <_GLOBAL_OFFSET_TABLE_+0x28>
400766: 68 02 00 00 00 pushq $0x2
40076b: e9 c0 ff ff ff jmpq 400730 <_init+0x18>
0000000000400770 <_ZNSt8ios_base4InitD1Ev#plt>:
400770: ff 25 a2 08 20 00 jmpq *0x2008a2(%rip) # 601018 <_GLOBAL_OFFSET_TABLE_+0x30>
400776: 68 03 00 00 00 pushq $0x3
40077b: e9 b0 ff ff ff jmpq 400730 <_init+0x18>
Disassembly of section .text:
0000000000400780 <_start>:
400780: 31 ed xor %ebp,%ebp
400782: 49 89 d1 mov %rdx,%r9
400785: 5e pop %rsi
400786: 48 89 e2 mov %rsp,%rdx
400789: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
40078d: 50 push %rax
40078e: 54 push %rsp
40078f: 49 c7 c0 80 09 40 00 mov $0x400980,%r8
400796: 48 c7 c1 f0 08 40 00 mov $0x4008f0,%rcx
40079d: 48 c7 c7 90 08 40 00 mov $0x400890,%rdi
4007a4: e8 a7 ff ff ff callq 400750 <__libc_start_main#plt>
4007a9: f4 hlt
4007aa: 90 nop
4007ab: 90 nop
00000000004007ac <call_gmon_start>:
4007ac: 48 83 ec 08 sub $0x8,%rsp
4007b0: 48 8b 05 29 08 20 00 mov 0x200829(%rip),%rax # 600fe0 <_DYNAMIC+0x1f0>
4007b7: 48 85 c0 test %rax,%rax
4007ba: 74 02 je 4007be <call_gmon_start+0x12>
4007bc: ff d0 callq *%rax
4007be: 48 83 c4 08 add $0x8,%rsp
4007c2: c3 retq
4007c3: 90 nop
4007c4: 90 nop
4007c5: 90 nop
4007c6: 90 nop
4007c7: 90 nop
4007c8: 90 nop
4007c9: 90 nop
4007ca: 90 nop
4007cb: 90 nop
4007cc: 90 nop
4007cd: 90 nop
4007ce: 90 nop
4007cf: 90 nop
00000000004007d0 <deregister_tm_clones>:
4007d0: b8 37 10 60 00 mov $0x601037,%eax
4007d5: 55 push %rbp
4007d6: 48 2d 30 10 60 00 sub $0x601030,%rax
4007dc: 48 83 f8 0e cmp $0xe,%rax
4007e0: 48 89 e5 mov %rsp,%rbp
4007e3: 77 02 ja 4007e7 <deregister_tm_clones+0x17>
4007e5: 5d pop %rbp
4007e6: c3 retq
4007e7: b8 00 00 00 00 mov $0x0,%eax
4007ec: 48 85 c0 test %rax,%rax
4007ef: 74 f4 je 4007e5 <deregister_tm_clones+0x15>
4007f1: 5d pop %rbp
4007f2: bf 30 10 60 00 mov $0x601030,%edi
4007f7: ff e0 jmpq *%rax
4007f9: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
0000000000400800 <register_tm_clones>:
400800: b8 30 10 60 00 mov $0x601030,%eax
400805: 55 push %rbp
400806: 48 2d 30 10 60 00 sub $0x601030,%rax
40080c: 48 c1 f8 03 sar $0x3,%rax
400810: 48 89 e5 mov %rsp,%rbp
400813: 48 89 c2 mov %rax,%rdx
400816: 48 c1 ea 3f shr $0x3f,%rdx
40081a: 48 01 d0 add %rdx,%rax
40081d: 48 d1 f8 sar %rax
400820: 75 02 jne 400824 <register_tm_clones+0x24>
400822: 5d pop %rbp
400823: c3 retq
400824: ba 00 00 00 00 mov $0x0,%edx
400829: 48 85 d2 test %rdx,%rdx
40082c: 74 f4 je 400822 <register_tm_clones+0x22>
40082e: 5d pop %rbp
40082f: 48 89 c6 mov %rax,%rsi
400832: bf 30 10 60 00 mov $0x601030,%edi
400837: ff e2 jmpq *%rdx
400839: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
0000000000400840 <__do_global_dtors_aux>:
400840: 80 3d e9 07 20 00 00 cmpb $0x0,0x2007e9(%rip) # 601030 <__bss_start>
400847: 75 11 jne 40085a <__do_global_dtors_aux+0x1a>
400849: 55 push %rbp
40084a: 48 89 e5 mov %rsp,%rbp
40084d: e8 7e ff ff ff callq 4007d0 <deregister_tm_clones>
400852: 5d pop %rbp
400853: c6 05 d6 07 20 00 01 movb $0x1,0x2007d6(%rip) # 601030 <__bss_start>
40085a: f3 c3 repz retq
40085c: 0f 1f 40 00 nopl 0x0(%rax)
0000000000400860 <frame_dummy>:
400860: 48 83 3d 80 05 20 00 cmpq $0x0,0x200580(%rip) # 600de8 <__JCR_END__>
400867: 00
400868: 74 1e je 400888 <frame_dummy+0x28>
40086a: b8 00 00 00 00 mov $0x0,%eax
40086f: 48 85 c0 test %rax,%rax
400872: 74 14 je 400888 <frame_dummy+0x28>
400874: 55 push %rbp
400875: bf e8 0d 60 00 mov $0x600de8,%edi
40087a: 48 89 e5 mov %rsp,%rbp
40087d: ff d0 callq *%rax
40087f: 5d pop %rbp
400880: e9 7b ff ff ff jmpq 400800 <register_tm_clones>
400885: 0f 1f 00 nopl (%rax)
400888: e9 73 ff ff ff jmpq 400800 <register_tm_clones>
40088d: 90 nop
40088e: 90 nop
40088f: 90 nop
0000000000400890 <main>:
400890: 55 push %rbp
400891: 48 89 e5 mov %rsp,%rbp
400894: b8 00 00 00 00 mov $0x0,%eax
400899: 5d pop %rbp
40089a: c3 retq
000000000040089b <_Z41__static_initialization_and_destruction_0ii>:
40089b: 55 push %rbp
40089c: 48 89 e5 mov %rsp,%rbp
40089f: 48 83 ec 10 sub $0x10,%rsp
4008a3: 89 7d fc mov %edi,-0x4(%rbp)
4008a6: 89 75 f8 mov %esi,-0x8(%rbp)
4008a9: 83 7d fc 01 cmpl $0x1,-0x4(%rbp)
4008ad: 75 27 jne 4008d6 <_Z41__static_initialization_and_destruction_0ii+0x3b>
4008af: 81 7d f8 ff ff 00 00 cmpl $0xffff,-0x8(%rbp)
4008b6: 75 1e jne 4008d6 <_Z41__static_initialization_and_destruction_0ii+0x3b>
4008b8: bf 34 10 60 00 mov $0x601034,%edi
4008bd: e8 7e fe ff ff callq 400740 <_ZNSt8ios_base4InitC1Ev#plt>
4008c2: ba 28 10 60 00 mov $0x601028,%edx
4008c7: be 34 10 60 00 mov $0x601034,%esi
4008cc: bf 70 07 40 00 mov $0x400770,%edi
4008d1: e8 8a fe ff ff callq 400760 <__cxa_atexit#plt>
4008d6: c9 leaveq
4008d7: c3 retq
00000000004008d8 <_GLOBAL__sub_I_main>:
4008d8: 55 push %rbp
4008d9: 48 89 e5 mov %rsp,%rbp
4008dc: be ff ff 00 00 mov $0xffff,%esi
4008e1: bf 01 00 00 00 mov $0x1,%edi
4008e6: e8 b0 ff ff ff callq 40089b <_Z41__static_initialization_and_destruction_0ii>
4008eb: 5d pop %rbp
4008ec: c3 retq
4008ed: 90 nop
4008ee: 90 nop
4008ef: 90 nop
00000000004008f0 <__libc_csu_init>:
4008f0: 48 89 6c 24 d8 mov %rbp,-0x28(%rsp)
4008f5: 4c 89 64 24 e0 mov %r12,-0x20(%rsp)
4008fa: 48 8d 2d df 04 20 00 lea 0x2004df(%rip),%rbp # 600de0 <__init_array_end>
400901: 4c 8d 25 c8 04 20 00 lea 0x2004c8(%rip),%r12 # 600dd0 <__frame_dummy_init_array_entry>
400908: 4c 89 6c 24 e8 mov %r13,-0x18(%rsp)
40090d: 4c 89 74 24 f0 mov %r14,-0x10(%rsp)
400912: 4c 89 7c 24 f8 mov %r15,-0x8(%rsp)
400917: 48 89 5c 24 d0 mov %rbx,-0x30(%rsp)
40091c: 48 83 ec 38 sub $0x38,%rsp
400920: 4c 29 e5 sub %r12,%rbp
400923: 41 89 fd mov %edi,%r13d
400926: 49 89 f6 mov %rsi,%r14
400929: 48 c1 fd 03 sar $0x3,%rbp
40092d: 49 89 d7 mov %rdx,%r15
400930: e8 e3 fd ff ff callq 400718 <_init>
400935: 48 85 ed test %rbp,%rbp
400938: 74 1c je 400956 <__libc_csu_init+0x66>
40093a: 31 db xor %ebx,%ebx
40093c: 0f 1f 40 00 nopl 0x0(%rax)
400940: 4c 89 fa mov %r15,%rdx
400943: 4c 89 f6 mov %r14,%rsi
400946: 44 89 ef mov %r13d,%edi
400949: 41 ff 14 dc callq *(%r12,%rbx,8)
40094d: 48 83 c3 01 add $0x1,%rbx
400951: 48 39 eb cmp %rbp,%rbx
400954: 75 ea jne 400940 <__libc_csu_init+0x50>
400956: 48 8b 5c 24 08 mov 0x8(%rsp),%rbx
40095b: 48 8b 6c 24 10 mov 0x10(%rsp),%rbp
400960: 4c 8b 64 24 18 mov 0x18(%rsp),%r12
400965: 4c 8b 6c 24 20 mov 0x20(%rsp),%r13
40096a: 4c 8b 74 24 28 mov 0x28(%rsp),%r14
40096f: 4c 8b 7c 24 30 mov 0x30(%rsp),%r15
400974: 48 83 c4 38 add $0x38,%rsp
400978: c3 retq
400979: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
0000000000400980 <__libc_csu_fini>:
400980: f3 c3 repz retq
400982: 90 nop
400983: 90 nop
Disassembly of section .fini:
0000000000400984 <_fini>:
400984: 48 83 ec 08 sub $0x8,%rsp
400988: 48 83 c4 08 add $0x8,%rsp
40098c: c3 retq
For completeness, I'm using:
Ubuntu: 12.04
Valgrind: 3.10.1 3.7.0
g++: 4.8.1
NB: As a side note, this does not happen when I include other headers such as <fstream> or <cmath>.
It's Valgrind's fault. First, -fsanitize=leak does not show anything. Second, Valgrind itself states that:
First of all: relax, it's probably not a bug, but a feature. Many
implementations of the C++ standard libraries use their own memory
pool allocators. Memory for quite a number of destructed objects is
not immediately freed and given back to the OS, but kept in the
pool(s) for later re-use. The fact that the pools are not freed at the
exit of the program cause Valgrind to report this memory as still
reachable. The behaviour not to free pools at the exit could be called
a bug of the library though.
Using GCC, you can force the STL to use malloc and to free memory as
soon as possible by globally disabling memory caching. Beware! Doing
so will probably slow down your program, sometimes drastically.
With GCC 2.91, 2.95, 3.0 and 3.1, compile all source using the STL
with -D__USE_MALLOC. Beware! This was removed from GCC starting with
version 3.3.
With GCC 3.2.2 and later, you should export the environment variable
GLIBCPP_FORCE_NEW before running your program.
With GCC 3.4 and later, that variable has changed name to
GLIBCXX_FORCE_NEW.
[...]
I guess those alleged memory pools are freed after program's termination, in the so-called start-up code that calls main, among the other settings. Internal functions defined outside user's code should be treated as if they didn't exist, that's why Valgrind can't (and shouldn't) see further frees.
Consider the following trivial include file:
#ifndef TRIVIAL_INCLUDE_FILE
#define TRIVIAL_INCLUDE_FILE
static int *x = new int (0);
#endif
For gcc 6 and higher, a related bug fix arrived:
Bug report: "Warning about "still reachable" memory when using libstdc++ from gcc 5"
Discussion on the Arch Linux bug tracker
With gcc 5, you can also get the same warning without including iostream.
So, if you see a similar warning referring to dl-init.c and you are using gcc 5, consider upgrading to a newer version (gcc >=6), or try to compile with clang.
EDIT:
I've voted to close this is it is now incorrect.
In March 2016 Valgrind gained an option "--run-cxx-freeres=<yes|no>" (default is yes). This will call a libstdc++ function to free one-off allocations used for things like iostream. If you are using a post-2016 Valgrind and libstdc++ you will get
==9356== HEAP SUMMARY:
==9356== in use at exit: 0 bytes in 0 blocks
==9356== total heap usage: 1 allocs, 1 frees, 72,704 bytes allocated
==9356==
==9356== All heap blocks were freed -- no leaks are possible
ORIGINAL POST:
Take the following trivial program:
#include <iostream>
int main() {
return 0;
}
If I run this using valgrind, I'm told that there are 72,704 bytes in 1 blocks that are still reachable. There have been extensive discussions on SO about whether or not to worry about still reachable warnings--I'm not concerned about that. I'd just like to understand how simply including a standard library header could cause a still reachable warning, when none of the objects from that library were allocated in the program itself.
Here is the full valgrind output:
$ valgrind --leak-check=full --track-origins=yes --show-reachable=yes ./ValgrindTest
==27671== Memcheck, a memory error detector
==27671== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==27671== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==27671== Command: ./ValgrindTest
==27671==
==27671==
==27671== HEAP SUMMARY:
==27671== in use at exit: 72,704 bytes in 1 blocks
==27671== total heap usage: 1 allocs, 0 frees, 72,704 bytes allocated
==27671==
==27671== 72,704 bytes in 1 blocks are still reachable in loss record 1 of 1
==27671== at 0x4C2AB9D: malloc (vg_replace_malloc.c:296)
==27671== by 0x4EC060F: ??? (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21)
==27671== by 0x400F305: call_init.part.0 (dl-init.c:85)
==27671== by 0x400F3DE: call_init (dl-init.c:52)
==27671== by 0x400F3DE: _dl_init (dl-init.c:134)
==27671== by 0x40016E9: ??? (in /lib/x86_64-linux-gnu/ld-2.15.so)
==27671==
==27671== LEAK SUMMARY:
==27671== definitely lost: 0 bytes in 0 blocks
==27671== indirectly lost: 0 bytes in 0 blocks
==27671== possibly lost: 0 bytes in 0 blocks
==27671== still reachable: 72,704 bytes in 1 blocks
==27671== suppressed: 0 bytes in 0 blocks
==27671==
==27671== For counts of detected and suppressed errors, rerun with: -v
==27671== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
And an object dump:
$ objdump -d ValgrindTest
ValgrindTest: file format elf64-x86-64
Disassembly of section .init:
0000000000400718 <_init>:
400718: 48 83 ec 08 sub $0x8,%rsp
40071c: e8 8b 00 00 00 callq 4007ac <call_gmon_start>
400721: 48 83 c4 08 add $0x8,%rsp
400725: c3 retq
Disassembly of section .plt:
0000000000400730 <_ZNSt8ios_base4InitC1Ev#plt-0x10>:
400730: ff 35 ba 08 20 00 pushq 0x2008ba(%rip) # 600ff0 <_GLOBAL_OFFSET_TABLE_+0x8>
400736: ff 25 bc 08 20 00 jmpq *0x2008bc(%rip) # 600ff8 <_GLOBAL_OFFSET_TABLE_+0x10>
40073c: 0f 1f 40 00 nopl 0x0(%rax)
0000000000400740 <_ZNSt8ios_base4InitC1Ev#plt>:
400740: ff 25 ba 08 20 00 jmpq *0x2008ba(%rip) # 601000 <_GLOBAL_OFFSET_TABLE_+0x18>
400746: 68 00 00 00 00 pushq $0x0
40074b: e9 e0 ff ff ff jmpq 400730 <_init+0x18>
0000000000400750 <__libc_start_main#plt>:
400750: ff 25 b2 08 20 00 jmpq *0x2008b2(%rip) # 601008 <_GLOBAL_OFFSET_TABLE_+0x20>
400756: 68 01 00 00 00 pushq $0x1
40075b: e9 d0 ff ff ff jmpq 400730 <_init+0x18>
0000000000400760 <__cxa_atexit#plt>:
400760: ff 25 aa 08 20 00 jmpq *0x2008aa(%rip) # 601010 <_GLOBAL_OFFSET_TABLE_+0x28>
400766: 68 02 00 00 00 pushq $0x2
40076b: e9 c0 ff ff ff jmpq 400730 <_init+0x18>
0000000000400770 <_ZNSt8ios_base4InitD1Ev#plt>:
400770: ff 25 a2 08 20 00 jmpq *0x2008a2(%rip) # 601018 <_GLOBAL_OFFSET_TABLE_+0x30>
400776: 68 03 00 00 00 pushq $0x3
40077b: e9 b0 ff ff ff jmpq 400730 <_init+0x18>
Disassembly of section .text:
0000000000400780 <_start>:
400780: 31 ed xor %ebp,%ebp
400782: 49 89 d1 mov %rdx,%r9
400785: 5e pop %rsi
400786: 48 89 e2 mov %rsp,%rdx
400789: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
40078d: 50 push %rax
40078e: 54 push %rsp
40078f: 49 c7 c0 80 09 40 00 mov $0x400980,%r8
400796: 48 c7 c1 f0 08 40 00 mov $0x4008f0,%rcx
40079d: 48 c7 c7 90 08 40 00 mov $0x400890,%rdi
4007a4: e8 a7 ff ff ff callq 400750 <__libc_start_main#plt>
4007a9: f4 hlt
4007aa: 90 nop
4007ab: 90 nop
00000000004007ac <call_gmon_start>:
4007ac: 48 83 ec 08 sub $0x8,%rsp
4007b0: 48 8b 05 29 08 20 00 mov 0x200829(%rip),%rax # 600fe0 <_DYNAMIC+0x1f0>
4007b7: 48 85 c0 test %rax,%rax
4007ba: 74 02 je 4007be <call_gmon_start+0x12>
4007bc: ff d0 callq *%rax
4007be: 48 83 c4 08 add $0x8,%rsp
4007c2: c3 retq
4007c3: 90 nop
4007c4: 90 nop
4007c5: 90 nop
4007c6: 90 nop
4007c7: 90 nop
4007c8: 90 nop
4007c9: 90 nop
4007ca: 90 nop
4007cb: 90 nop
4007cc: 90 nop
4007cd: 90 nop
4007ce: 90 nop
4007cf: 90 nop
00000000004007d0 <deregister_tm_clones>:
4007d0: b8 37 10 60 00 mov $0x601037,%eax
4007d5: 55 push %rbp
4007d6: 48 2d 30 10 60 00 sub $0x601030,%rax
4007dc: 48 83 f8 0e cmp $0xe,%rax
4007e0: 48 89 e5 mov %rsp,%rbp
4007e3: 77 02 ja 4007e7 <deregister_tm_clones+0x17>
4007e5: 5d pop %rbp
4007e6: c3 retq
4007e7: b8 00 00 00 00 mov $0x0,%eax
4007ec: 48 85 c0 test %rax,%rax
4007ef: 74 f4 je 4007e5 <deregister_tm_clones+0x15>
4007f1: 5d pop %rbp
4007f2: bf 30 10 60 00 mov $0x601030,%edi
4007f7: ff e0 jmpq *%rax
4007f9: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
0000000000400800 <register_tm_clones>:
400800: b8 30 10 60 00 mov $0x601030,%eax
400805: 55 push %rbp
400806: 48 2d 30 10 60 00 sub $0x601030,%rax
40080c: 48 c1 f8 03 sar $0x3,%rax
400810: 48 89 e5 mov %rsp,%rbp
400813: 48 89 c2 mov %rax,%rdx
400816: 48 c1 ea 3f shr $0x3f,%rdx
40081a: 48 01 d0 add %rdx,%rax
40081d: 48 d1 f8 sar %rax
400820: 75 02 jne 400824 <register_tm_clones+0x24>
400822: 5d pop %rbp
400823: c3 retq
400824: ba 00 00 00 00 mov $0x0,%edx
400829: 48 85 d2 test %rdx,%rdx
40082c: 74 f4 je 400822 <register_tm_clones+0x22>
40082e: 5d pop %rbp
40082f: 48 89 c6 mov %rax,%rsi
400832: bf 30 10 60 00 mov $0x601030,%edi
400837: ff e2 jmpq *%rdx
400839: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
0000000000400840 <__do_global_dtors_aux>:
400840: 80 3d e9 07 20 00 00 cmpb $0x0,0x2007e9(%rip) # 601030 <__bss_start>
400847: 75 11 jne 40085a <__do_global_dtors_aux+0x1a>
400849: 55 push %rbp
40084a: 48 89 e5 mov %rsp,%rbp
40084d: e8 7e ff ff ff callq 4007d0 <deregister_tm_clones>
400852: 5d pop %rbp
400853: c6 05 d6 07 20 00 01 movb $0x1,0x2007d6(%rip) # 601030 <__bss_start>
40085a: f3 c3 repz retq
40085c: 0f 1f 40 00 nopl 0x0(%rax)
0000000000400860 <frame_dummy>:
400860: 48 83 3d 80 05 20 00 cmpq $0x0,0x200580(%rip) # 600de8 <__JCR_END__>
400867: 00
400868: 74 1e je 400888 <frame_dummy+0x28>
40086a: b8 00 00 00 00 mov $0x0,%eax
40086f: 48 85 c0 test %rax,%rax
400872: 74 14 je 400888 <frame_dummy+0x28>
400874: 55 push %rbp
400875: bf e8 0d 60 00 mov $0x600de8,%edi
40087a: 48 89 e5 mov %rsp,%rbp
40087d: ff d0 callq *%rax
40087f: 5d pop %rbp
400880: e9 7b ff ff ff jmpq 400800 <register_tm_clones>
400885: 0f 1f 00 nopl (%rax)
400888: e9 73 ff ff ff jmpq 400800 <register_tm_clones>
40088d: 90 nop
40088e: 90 nop
40088f: 90 nop
0000000000400890 <main>:
400890: 55 push %rbp
400891: 48 89 e5 mov %rsp,%rbp
400894: b8 00 00 00 00 mov $0x0,%eax
400899: 5d pop %rbp
40089a: c3 retq
000000000040089b <_Z41__static_initialization_and_destruction_0ii>:
40089b: 55 push %rbp
40089c: 48 89 e5 mov %rsp,%rbp
40089f: 48 83 ec 10 sub $0x10,%rsp
4008a3: 89 7d fc mov %edi,-0x4(%rbp)
4008a6: 89 75 f8 mov %esi,-0x8(%rbp)
4008a9: 83 7d fc 01 cmpl $0x1,-0x4(%rbp)
4008ad: 75 27 jne 4008d6 <_Z41__static_initialization_and_destruction_0ii+0x3b>
4008af: 81 7d f8 ff ff 00 00 cmpl $0xffff,-0x8(%rbp)
4008b6: 75 1e jne 4008d6 <_Z41__static_initialization_and_destruction_0ii+0x3b>
4008b8: bf 34 10 60 00 mov $0x601034,%edi
4008bd: e8 7e fe ff ff callq 400740 <_ZNSt8ios_base4InitC1Ev#plt>
4008c2: ba 28 10 60 00 mov $0x601028,%edx
4008c7: be 34 10 60 00 mov $0x601034,%esi
4008cc: bf 70 07 40 00 mov $0x400770,%edi
4008d1: e8 8a fe ff ff callq 400760 <__cxa_atexit#plt>
4008d6: c9 leaveq
4008d7: c3 retq
00000000004008d8 <_GLOBAL__sub_I_main>:
4008d8: 55 push %rbp
4008d9: 48 89 e5 mov %rsp,%rbp
4008dc: be ff ff 00 00 mov $0xffff,%esi
4008e1: bf 01 00 00 00 mov $0x1,%edi
4008e6: e8 b0 ff ff ff callq 40089b <_Z41__static_initialization_and_destruction_0ii>
4008eb: 5d pop %rbp
4008ec: c3 retq
4008ed: 90 nop
4008ee: 90 nop
4008ef: 90 nop
00000000004008f0 <__libc_csu_init>:
4008f0: 48 89 6c 24 d8 mov %rbp,-0x28(%rsp)
4008f5: 4c 89 64 24 e0 mov %r12,-0x20(%rsp)
4008fa: 48 8d 2d df 04 20 00 lea 0x2004df(%rip),%rbp # 600de0 <__init_array_end>
400901: 4c 8d 25 c8 04 20 00 lea 0x2004c8(%rip),%r12 # 600dd0 <__frame_dummy_init_array_entry>
400908: 4c 89 6c 24 e8 mov %r13,-0x18(%rsp)
40090d: 4c 89 74 24 f0 mov %r14,-0x10(%rsp)
400912: 4c 89 7c 24 f8 mov %r15,-0x8(%rsp)
400917: 48 89 5c 24 d0 mov %rbx,-0x30(%rsp)
40091c: 48 83 ec 38 sub $0x38,%rsp
400920: 4c 29 e5 sub %r12,%rbp
400923: 41 89 fd mov %edi,%r13d
400926: 49 89 f6 mov %rsi,%r14
400929: 48 c1 fd 03 sar $0x3,%rbp
40092d: 49 89 d7 mov %rdx,%r15
400930: e8 e3 fd ff ff callq 400718 <_init>
400935: 48 85 ed test %rbp,%rbp
400938: 74 1c je 400956 <__libc_csu_init+0x66>
40093a: 31 db xor %ebx,%ebx
40093c: 0f 1f 40 00 nopl 0x0(%rax)
400940: 4c 89 fa mov %r15,%rdx
400943: 4c 89 f6 mov %r14,%rsi
400946: 44 89 ef mov %r13d,%edi
400949: 41 ff 14 dc callq *(%r12,%rbx,8)
40094d: 48 83 c3 01 add $0x1,%rbx
400951: 48 39 eb cmp %rbp,%rbx
400954: 75 ea jne 400940 <__libc_csu_init+0x50>
400956: 48 8b 5c 24 08 mov 0x8(%rsp),%rbx
40095b: 48 8b 6c 24 10 mov 0x10(%rsp),%rbp
400960: 4c 8b 64 24 18 mov 0x18(%rsp),%r12
400965: 4c 8b 6c 24 20 mov 0x20(%rsp),%r13
40096a: 4c 8b 74 24 28 mov 0x28(%rsp),%r14
40096f: 4c 8b 7c 24 30 mov 0x30(%rsp),%r15
400974: 48 83 c4 38 add $0x38,%rsp
400978: c3 retq
400979: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
0000000000400980 <__libc_csu_fini>:
400980: f3 c3 repz retq
400982: 90 nop
400983: 90 nop
Disassembly of section .fini:
0000000000400984 <_fini>:
400984: 48 83 ec 08 sub $0x8,%rsp
400988: 48 83 c4 08 add $0x8,%rsp
40098c: c3 retq
For completeness, I'm using:
Ubuntu: 12.04
Valgrind: 3.10.1 3.7.0
g++: 4.8.1
NB: As a side note, this does not happen when I include other headers such as <fstream> or <cmath>.
It's Valgrind's fault. First, -fsanitize=leak does not show anything. Second, Valgrind itself states that:
First of all: relax, it's probably not a bug, but a feature. Many
implementations of the C++ standard libraries use their own memory
pool allocators. Memory for quite a number of destructed objects is
not immediately freed and given back to the OS, but kept in the
pool(s) for later re-use. The fact that the pools are not freed at the
exit of the program cause Valgrind to report this memory as still
reachable. The behaviour not to free pools at the exit could be called
a bug of the library though.
Using GCC, you can force the STL to use malloc and to free memory as
soon as possible by globally disabling memory caching. Beware! Doing
so will probably slow down your program, sometimes drastically.
With GCC 2.91, 2.95, 3.0 and 3.1, compile all source using the STL
with -D__USE_MALLOC. Beware! This was removed from GCC starting with
version 3.3.
With GCC 3.2.2 and later, you should export the environment variable
GLIBCPP_FORCE_NEW before running your program.
With GCC 3.4 and later, that variable has changed name to
GLIBCXX_FORCE_NEW.
[...]
I guess those alleged memory pools are freed after program's termination, in the so-called start-up code that calls main, among the other settings. Internal functions defined outside user's code should be treated as if they didn't exist, that's why Valgrind can't (and shouldn't) see further frees.
Consider the following trivial include file:
#ifndef TRIVIAL_INCLUDE_FILE
#define TRIVIAL_INCLUDE_FILE
static int *x = new int (0);
#endif
For gcc 6 and higher, a related bug fix arrived:
Bug report: "Warning about "still reachable" memory when using libstdc++ from gcc 5"
Discussion on the Arch Linux bug tracker
With gcc 5, you can also get the same warning without including iostream.
So, if you see a similar warning referring to dl-init.c and you are using gcc 5, consider upgrading to a newer version (gcc >=6), or try to compile with clang.
I am trying to compile a source with tcc (ver 0.9.26) against a gcc-generated .o file, but it has strange behavior. The gcc (ver 5.3.0)is from MinGW 64 bit.
More specifically, I have the following two files (te1.c te2.c). I did the following commands on windows7 box
c:\tcc> gcc -c te1.c
c:\tcc> objcopy -O elf64-x86-64 te1.o #this is needed because te1.o from previous step is in COFF format, tcc only understand ELF format
c:\tcc> tcc te2.c te1.o
c:\tcc> te2.exe
567in dummy!!!
Note that it cut off 4 bytes from the string 1234567in dummy!!!\n. Wonder if what could have gone wrong.
Thanks
Jin
========file te1.c===========
#include <stdio.h>
void dummy () {
printf1("1234567in dummy!!!\n");
}
========file te2.c===========
#include <stdio.h>
void printf1(char *p) {
printf("%s\n",p);
}
extern void dummy();
int main(int argc, char *argv[]) {
dummy();
return 0;
}
Update 1
Saw a difference in assembly between te1.o (te1.c compiled by tcc) and te1_gcc.o (te1.c compiled by gcc). In the tcc compiled, I saw lea -0x4(%rip),%rcx, on the gcc compiled, I saw lea 0x0(%rip),%rcx.
Not sure why.
C:\temp>objdump -d te1.o
te1.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <dummy>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 48 81 ec 20 00 00 00 sub $0x20,%rsp
b: 48 8d 0d fc ff ff ff lea -0x4(%rip),%rcx # e <dummy+0xe>
12: e8 fc ff ff ff callq 13 <dummy+0x13>
17: c9 leaveq
18: c3 retq
19: 00 00 add %al,(%rax)
1b: 00 01 add %al,(%rcx)
1d: 04 02 add $0x2,%al
1f: 05 04 03 01 50 add $0x50010304,%eax
C:\temp>objdump -d te1_gcc.o
te1_gcc.o: file format pe-x86-64
Disassembly of section .text:
0000000000000000 <dummy>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 48 83 ec 20 sub $0x20,%rsp
8: 48 8d 0d 00 00 00 00 lea 0x0(%rip),%rcx # f <dummy+0xf>
f: e8 00 00 00 00 callq 14 <dummy+0x14>
14: 90 nop
15: 48 83 c4 20 add $0x20,%rsp
19: 5d pop %rbp
1a: c3 retq
1b: 90 nop
1c: 90 nop
1d: 90 nop
1e: 90 nop
1f: 90 nop
Update2
Using a binary editor, I changed the machine code in te1.o (produced by gcc) and changed lea 0(%rip),%rcx to lea -0x4(%rip),%rcx and using the tcc to link it, the resulted exe works fine.
More precisely, I did
c:\tcc> gcc -c te1.c
c:\tcc> objcopy -O elf64-x86-64 te1.o
c:\tcc> use a binary editor to the change the bytes from (48 8d 0d 00 00 00 00) to (48 8d 0d fc ff ff ff)
c:\tcc> tcc te2.c te1.o
c:\tcc> te2
1234567in dummy!!!
Update 3
As requested, here is the output of objdump -r te1.o
C:\temp>gcc -c te1.c
C:\temp>objdump -r te1.o
te1.o: file format pe-x86-64
RELOCATION RECORDS FOR [.text]:
OFFSET TYPE VALUE
000000000000000b R_X86_64_PC32 .rdata
0000000000000010 R_X86_64_PC32 printf1
RELOCATION RECORDS FOR [.pdata]:
OFFSET TYPE VALUE
0000000000000000 rva32 .text
0000000000000004 rva32 .text
0000000000000008 rva32 .xdata
C:\temp>objdump -d te1.o
te1.o: file format pe-x86-64
Disassembly of section .text:
0000000000000000 <dummy>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 48 83 ec 20 sub $0x20,%rsp
8: 48 8d 0d 00 00 00 00 lea 0x0(%rip),%rcx # f <dummy+0xf>
f: e8 00 00 00 00 callq 14 <dummy+0x14>
14: 90 nop
15: 48 83 c4 20 add $0x20,%rsp
19: 5d pop %rbp
1a: c3 retq
1b: 90 nop
1c: 90 nop
1d: 90 nop
1e: 90 nop
1f: 90 nop
Has nothing to do with tcc or calling conventions. It has to do with different linker conventions for elf64-x86-64 and pe-x86-64 formats.
With PE, the linker will subtract 4 implicitly to calculate the final offset.
With ELF, it does not do this. Because of this, 0 is the correct initial value for PE, and -4 is correct for ELF.
Unfortunately, objcopy does not convert this -> bug in objcopy.
add
extern void printf1(char *p);
to your te1.c file
Or: the compiler will assume argument 32 bit integer since there's no prototype, and pointers are 64-bit long.
Edit: this is still not working. I found out that the function never returns (since calling the printf1 a second time does nothing!). Seems that the 4 first bytes are consumed as return address or something like that. In gcc 32-bit mode it works fine.
Sounds like a calling convention problem to me but still cannot figure it out.
Another clue: calling printf from te1.c side (gcc, using tcc stdlib bindings) crashes with segv.
I disassembled the executable. First part is repeated call from tcc side
40104f: 48 8d 05 b3 0f 00 00 lea 0xfb3(%rip),%rax # 0x402009
401056: 48 89 45 f8 mov %rax,-0x8(%rbp)
40105a: 48 8b 4d f8 mov -0x8(%rbp),%rcx
40105e: e8 9d ff ff ff callq 0x401000
401063: 48 8b 4d f8 mov -0x8(%rbp),%rcx
401067: e8 94 ff ff ff callq 0x401000
40106c: 48 8b 4d f8 mov -0x8(%rbp),%rcx
401070: e8 8b ff ff ff callq 0x401000
401075: 48 8b 4d f8 mov -0x8(%rbp),%rcx
401079: e8 82 ff ff ff callq 0x401000
40107e: e8 0d 00 00 00 callq 0x401090
401083: b8 00 00 00 00 mov $0x0,%eax
401088: e9 00 00 00 00 jmpq 0x40108d
40108d: c9 leaveq
40108e: c3 retq
Second part is repeated (6 times) call to the same function. As you can see the address is different (shifted by 4 bytes, like your data) !!! It kind of works just once because the 4 first instructions are the following:
401000: 55 push %rbp
401001: 48 89 e5 mov %rsp,%rbp
so stack is destroyed if those are skipped!!
40109f: 48 89 45 f8 mov %rax,-0x8(%rbp)
4010a3: 48 8b 45 f8 mov -0x8(%rbp),%rax
4010a7: 48 89 c1 mov %rax,%rcx
4010aa: e8 55 ff ff ff callq 0x401004
4010af: 48 8b 45 f8 mov -0x8(%rbp),%rax
4010b3: 48 89 c1 mov %rax,%rcx
4010b6: e8 49 ff ff ff callq 0x401004
4010bb: 48 8b 45 f8 mov -0x8(%rbp),%rax
4010bf: 48 89 c1 mov %rax,%rcx
4010c2: e8 3d ff ff ff callq 0x401004
4010c7: 48 8b 45 f8 mov -0x8(%rbp),%rax
4010cb: 48 89 c1 mov %rax,%rcx
4010ce: e8 31 ff ff ff callq 0x401004
4010d3: 48 8b 45 f8 mov -0x8(%rbp),%rax
4010d7: 48 89 c1 mov %rax,%rcx
4010da: e8 25 ff ff ff callq 0x401004
4010df: 48 8b 45 f8 mov -0x8(%rbp),%rax
4010e3: 48 89 c1 mov %rax,%rcx
4010e6: e8 19 ff ff ff callq 0x401004
4010eb: 90 nop
I've compiled some Qt code with google's nacl compiler, but the ncval validator does not grok it. One example among many:
src/corelib/animation/qabstractanimation.cpp:165
Here's the relevant code:
#define Q_GLOBAL_STATIC(TYPE, NAME) \
static TYPE *NAME() \
{ \
static TYPE thisVariable; \
static QGlobalStatic<TYPE > thisGlobalStatic(&thisVariable); \
return thisGlobalStatic.pointer; \
}
#ifndef QT_NO_THREAD
Q_GLOBAL_STATIC(QThreadStorage<QUnifiedTimer *>, unifiedTimer)
#endif
which compiles to:
00000480 <_ZL12unifiedTimerv>:
480: 55 push %ebp
481: 89 e5 mov %esp,%ebp
483: 57 push %edi
484: 56 push %esi
485: 53 push %ebx
486: 83 ec 2c sub $0x2c,%esp
489: c7 04 24 28 00 2e 10 movl $0x102e0028,(%esp)
490: 8d 74 26 00 lea 0x0(%esi,%eiz,1),%esi
494: 8d bc 27 00 00 00 00 lea 0x0(%edi,%eiz,1),%edi
49b: e8 fc ff ff ff call 49c <_ZL12unifiedTimerv+0x1c>
4a0: 84 c0 test %al,%al
4a2: 74 1c je 4c0 <_ZL12unifiedTimerv+0x40>
4a4: 0f b6 05 2c 00 2e 10 movzbl 0x102e002c,%eax
4ab: 83 f0 01 xor $0x1,%eax
4ae: 84 c0 test %al,%al
4b0: 74 0e je 4c0 <_ZL12unifiedTimerv+0x40>
4b2: b8 01 00 00 00 mov $0x1,%eax
4b7: eb 27 jmp 4e0 <_ZL12unifiedTimerv+0x60>
4b9: 8d b4 26 00 00 00 00 lea 0x0(%esi,%eiz,1),%esi
4c0: b8 00 00 00 00 mov $0x0,%eax
4c5: eb 19 jmp 4e0 <_ZL12unifiedTimerv+0x60>
4c7: 90 nop
4c8: 90 nop
4c9: 90 nop
4ca: 90 nop
4cb: 90 nop
Check the call instruction at 49b: it is what the validator cannot grok. What on earth could induce the compiler to issue an instruction that calls into the middle of itself? Is there a way around this? I've compiled with -g -O0 -fno-inline. Compiler bug?
Presumably it's really a call to an external symbol, which will get filled in at link time. Actually what will get called is externalSymbol-4, which is a bit strange -- perhaps this is what is throwing the ncval validator off the scent.
Is this a dynamic library or a static object that is not linked to an executable yet?
In a dynamic library this likely came out because the code was built as position-dependent and linked into a dynamic library. Try "objdump -d -r -R" on it, if you see TEXTREL, that is the case. TEXTREL is not supported in NaCl dynamic linking stories. (solved by having -fPIC flag during compilation of the code)
With a static object try to validate after it was linked into a static executable.