For some reason I reinstalled my OS(manjaro linux) yesterday, and installed gcc and gdb by pacman, then I write a very small example program to make sure my environment is correct, because I am a beginner in linux and gdb. After compile，it went according to my expectations. Then I wanted to take a look at the STL source code through gdb, so I opened my gdb with tui mode. Everything seemed normal at first, but my gdb can't step into ss.insert() that I want to see, with [ No Source Available ] on the top side of the screen. And I've found the directory of the source file of operator<< is different to the version that before reinstall OS, and /usr/shared/c++/ doesn't exist anymore!
This is the version information of GCC(g++) and gdb
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc/src/gcc/configure --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/ --enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++,d --with-isl --with-linker-hash-style=gnu --with-system-zlib --enable-__cxa_atexit --enable-cet=auto --enable-checking=release --enable-clocale=gnu --enable-default-pie --enable-default-ssp --enable-gnu-indirect-function --enable-gnu-unique-object --enable-install-libiberty --enable-linker-build-id --enable-lto --enable-multilib --enable-plugin --enable-shared --enable-threads=posix --disable-libssp --disable-libstdcxx-pch --disable-libunwind-exceptions --disable-werror gdc_include_dir=/usr/include/dlang/gdc
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.2.0 (GCC)
GNU gdb (GDB) 10.1
Copyright (C) 2020 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Why gdb complain to me that No Source Available (with g++ -ggdb3)
Because you are stopped inside libstdc++, which was built in a temporary directory (here /build/gcc/src/gcc-build/...) and that directory is not present on your machine.
It is exceedingly unlikely that you actually need to look at the source of operator<<(), but if you really do want to do that, install GCC sources, and use (gdb) directory to point GDB to the relevant sources.
Related
I stumbled upon very strange issue with GCC. The issue is 25% drop in performance. Here is the story.
I have a pice of software which is fp32 compute intensive (neural networks compiled with TVM). I compile it for ARM (rk3399 device), here is info:
gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/arm-linux-gnueabihf/5/lto-wrapper
Target: arm-linux-gnueabihf
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.12' --with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs --enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-5 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-libitm --disable-libquadmath --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-armhf/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-armhf --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-armhf --with-arch-directory=arm --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --enable-multilib --disable-sjlj-exceptions --with-arch=armv7-a --with-fpu=vfpv3-d16 --with-float=hard --with-mode=thumb --disable-werror --enable-multilib --enable-checking=release --build=arm-linux-gnueabihf --host=arm-linux-gnueabihf --target=arm-linux-gnueabihf
Thread model: posix
gcc version 5.4.0 20160609 (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.12)
uname -a
Linux FriendlyELEC 4.4.143 #1 SMP Tue Nov 20 11:10:11 CST 2018 aarch64 aarch64 aarch64 GNU/Linux
lscpu
Architecture: aarch64
Byte Order: Little Endian
CPU(s): 6
On-line CPU(s) list: 0-5
Thread(s) per core: 1
Core(s) per socket: 3
Socket(s): 2
Model name: ARMv8 Processor rev 2 (v8l)
CPU max MHz: 1800.0000
CPU min MHz: 408.0000
Hypervisor vendor: horizontal
Virtualization type: full
The code was initially "slow" and cpp11, I decided to try cpp17 and cpp14. cpp17 was not supported, but cpp14 was. I switched to cpp14 and voila I got boost around 25% in performance. I really tested it to make sure the boost is in fact real and not a measuring mistake. I had this boost for a week then my device rebooted and the boost in performance was gone!
It may sound crazy, but I'm very sure in my code and measurements I had. I didn't have explicit compile flags prior to this gimmick. Now I'm trying to figure out compile flags for GCC to reclaim what was lost, but I don't have much experience with GCC. What could be the issue here? What flags can affect performance that much?
the code uses .so files, compiled with use of llvm and gcc
llvm -device=arm_cpu -target=armv8l-linux-gnueabihf -mattr=+neon,fp-armv8
"What flags can affect performance that much?"
Turning on the optimizer -O1, -O2 or -O3 can have a dramatic effect (default is unoptimized build -O0).
Enabling link time optimization -flto can also often give significant improvements.
See also the manual for more.
It's not GCC fault. It's CPU frequency scaling problem. I had device with ARM with Linux (ubuntu) on board, strange behavior and different benchmarking results are due to strange cpu frequency governing by OS.
Once O tried to compile Fortran code that relies on funits. while it is not available in gfortran 4.9.3.
use FUNITS
1
Fatal Error: Can't open module file 'funits.mod' for reading at (1): No such file or directory
here is gfortran information
gfortran -v
Using built-in specs.
COLLECT_GCC=/usr/x86_64-pc-linux-gnu/gcc-bin/4.9.3/gfortran
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/4.9.3/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /var/tmp/portage/sys-devel/gcc-4.9.3/work/gcc-4.9.3/configure --host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/4.9.3 --includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/include --datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.9.3 --mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.9.3/man --infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.9.3/info --with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/include/g++-v4 --with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/4.9.3/python --enable-languages=c,c++,java,fortran --enable-obsolete --enable-secureplt --disable-werror --with-system-zlib --enable-nls --without-included-gettext --enable-checking=release --with-bugurl=https://bugs.gentoo.org/ --with-pkgversion='Gentoo 4.9.3 p1.5, pie-0.6.4' --enable-libstdcxx-time --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --enable-multilib --with-multilib-list=m32,m64 --disable-altivec --disable-fixed-point --enable-targets=all --enable-libgomp --disable-libmudflap --disable-libssp --disable-libcilkrts --enable-vtable-verify --enable-libvtv --enable-lto --without-cloog --enable-libsanitizer
Thread model: posix
gcc version 4.9.3 (Gentoo 4.9.3 p1.5, pie-0.6.4)
Instead ifort version 14.0.3 has it pre-installed.
How can I install funits with gfortran as we need to rely on the free software?
FUNITS is a module. There is no such module in standard Fortran. It must be some external library, not an intrinsic module.
It is also not part of Intel Fortran although you claim it to be. It is not part of my Intel Fortran installation and it is not mentioned anywhere in the manual.
You have to find where does it come from, who supplies this library and compile it for gfortran yourself.
Or find out what it does and implement that functionality yourself.
A simple web search found 2 modules called FUNITS on the internet. Both just declare some file unit number constants. I have no idea whether you need one of them or not https://mfix.netl.doe.gov/develop/STI/source_profile_2015-2/mfix_und/MFIX_html/9899.html http://home.chpc.utah.edu/~u0703457/STILT_tutorial/WRF_STILT_code/STILT_updated/funits.f Probably it will be better to search your hard drive.
I'm trying to find the median of vectors of (x,y) points using nth_element
cv::Point2f medOffset;
vector<float> tempOffsetsX = offsetsX;
int medLoc = tempOffsetsX.size()/2;
nth_element(tempOffsetsX.begin(), tempOffsetsX.begin()+medLoc, tempOffsetsX.end());
// sort(tempOffsetsX.begin(), tempOffsetsX.end());
medOffset.x = tempOffsetsX[medLoc];
vector<float> tempOffsetsY = offsetsY;
****** debug out line 1 *********
nth_element(tempOffsetsY.begin(), tempOffsetsY.begin()+medLoc, tempOffsetsY.end());
// sort(tempOffsetsY.begin(), tempOffsetsY.end());
medOffset.y = tempOffsetsY[medLoc];
****** debug out line 2 *********
tempOffsetsX is working just fine but, occasionally, tempOffsetsY is giving very strange results after nth_element. Here is sample output at the marked debug lines
tempOffsetsY1: 5.184135 -1.564125 3.751759 0.221855 -0.742348 1.737648
tempOffsetsY2: -0.742348 -1.564125 -8885092352.000000 -8850636800.000000 0.000000 0.000000
The results are pretty repeatable until I recompile, at which point the specifics change the the general problem remains. Clearly the vector is getting corrupted somehow but I can't think of how.
Also, if I use sort instead of nth_element it works without problem. For debugging, I tried doing a sort and then nth_element which worked just fine. So somehow the reordering that happens inside nth_element is getting messed up but I can't think of how.
Any ideas how this is happening?
edit - More info about my environment. I'm running Arch Linux. I just did a system update. I should note that this same code did work without problem before the update, and this is the first time I've ran it after the update. But that's a gap of several days and I'm always hesitant to point at system libraries for what is usually my own problem.
[]$ uname -r
3.11.6-1-ARCH
[]$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-unknown-linux-gnu/4.8.2/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: /build/gcc/src/gcc-4.8.2/configure --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/ --enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared --enable-threads=posix --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch --enable-gnu-unique-object --enable-linker-build-id --enable-cloog-backend=isl --disable-cloog-version-check --enable-lto --enable-gold --enable-ld=default --enable-plugin --with-plugin-ld=ld.gold --with-linker-hash-style=gnu --disable-install-libiberty --disable-multilib --disable-libssp --disable-werror --enable-checking=release
Thread model: posix
gcc version 4.8.2 (GCC)
[]$ pacman -Qi glibc
Name : glibc
Version : 2.18-8
....
Quite likely you're running into a recent bug in libstdc++, which broke the nth_element function. This has since been fixed, but some Linux releases shipped with the broken version (e.g. Ubuntu 13.10)
A patch and discussion of the bug can be found on the GCC tracker: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58800
Environment:
Ubuntu, GCC 4.6.3
Using Qt 4.8
By default, my include search order (as reported by gcc -v) is:
<clipped out my project specific includes>
/usr/include/c++/4.6
/usr/include/c++/4.6/x86_64-linux-gnu/.
/usr/include/c++/4.6/backward
/usr/lib/gcc/x86_64-linux-gnu/4.6/include
/usr/local/include
/usr/lib/gcc/x86_64-linux-gnu/4.6/include-fixed
/usr/include/x86_64-linux-gnu
/usr/include
I am trying to archive this build environment so that it doesn't build from the actual system folders, but only from a source tree that is checked-in and well-defined if my machine is recreated. I am running into issues overriding the system search paths for gcc.
Specifically, I first tried --sysroot=../../sysroot, but only the last two include folders changed:
/usr/include/c++/4.6
/usr/include/c++/4.6/x86_64-linux-gnu/.
/usr/include/c++/4.6/backward
/usr/lib/gcc/x86_64-linux-gnu/4.6/include
/usr/lib/gcc/x86_64-linux-gnu/4.6/include-fixed
../../sysroot/usr/include/x86_64-linux-gnu
../../sysroot/usr/include
GCC -v reports:
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.6/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v
--with-pkgversion='Ubuntu/Linaro 4.6.3-1ubuntu5'
--with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.6
--enable-shared --enable-linker-build-id --with-system-zlib
--libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.6 --libdir=/usr/lib
--enable-nls
--with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin
--enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5)
So it appears that the /usr/lib/... and /usr/include... lines may be coming from the built-in GCC configuration. I'm a GCC/G++ noob, so I could be wrong here - please correct as appropriate.
At any rate, my question is how I change my configuration so that these folders:
/usr/include/c++/4.6
/usr/include/c++/4.6/x86_64-linux-gnu/.
/usr/include/c++/4.6/backward
/usr/lib/gcc/x86_64-linux-gnu/4.6/include
/usr/lib/gcc/x86_64-linux-gnu/4.6/include-fixed
are also relative to ../../sysroot?
(To be clear, I know about -I and these are not being specified on the command line, or in the make file.)
I can get almost the right result by using -nostdinc and specifying each folder directly (with -I), except the Qt Meta-Object-Compiler fails when it is fed some of these system include folders. Because I am using Qt, I want to change GCC's configured search paths instead of just listing every single system folder individually with -I.
Any advice would be greatly appreciated.
Thanks,
Brad
Just as one of possible solution directions, maybe too much for your case:
Actually as I understand what you are trying to achieve is close to cross-compilation against different system image. This task is very common in embedded development though it is not so easy. Most of idea is to build GCC so it 'thinks' system image is in place different from normal.
This link should at least help you to understand basic principles.
This is another and what's more it contains other useful links like cross-compiling FAQ.
I'm debugging somebody else's Qt program and ran into the following error message which I don't understand:
DWARF-2 expression error: DW_OP_reg operations must be used either alone or in
conjuction with DW_OP_piece or DW_OP_bit_piece.
I'm not sure what that means and Google isn't of much help.
Here's the context - sLocation is a QString that was declared a few lines earlier. However, it was created from functions which were inlined, so I'm not sure of its value and am attempting to check before being appended to:
(gdb) printqstring suffix
(QString)0xffffbd80: "sorted"
(gdb) next
1241 sLocation += suffix;
(gdb) printqstring sLocation
Can't take address of "sLocation" which isn't an lvalue.
(gdb) info local
sLocation = <error reading variable sLocation (DWARF-2 expression error:
DW_OP_reg operations must be used either alone or in conjuction with
DW_OP_piece or DW_OP_bit_piece.)>
Could somebody please explain what that error message means or what could cause it?
The error message means that GDB is reading DWARF2 debug info from the executable, and is rejecting that info as invalid (not following the DWARF2 standard).
The invalid info is likely due to a bug in GCC, fixed in SVN revision 147187:
2009-05-06 Jakub Jelinek <jakub#redhat.com>
* dwarf2out.c (new_reg_loc_descr): Don't ever create DW_OP_regX.
(one_reg_loc_descriptor): Create DW_OP_regX here instead of calling
new_reg_loc_descr.
(loc_by_reference): If loc is DW_OP_regX, change it into DW_OP_bregX 0
instead of appending DW_OP_deref*.
I got the same problem running a Ubuntu 10.10 64bit. However, the same code on a 10.04 LTS 32bit works perfectly.
Here is the version output of both setups
Ubuntu 10.10:
$ gcc -v
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.4.4-14ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.4 --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.4.5 (Ubuntu/Linaro 4.4.4-14ubuntu5)
GCC on 10.04 LTS:
$ gcc -v
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.4.3-4ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-plugin --enable-objc-gc --enable-targets=all --disable-werror --with-arch-32=i486 --with-tune=generic --enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu --target=i486-linux-gnu
Thread model: posix
gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5
Cheers,
Andre