Under command line, I know that using echo $? gets me the exit code. In gdb, I use "r" to run through the program and the program terminates, so how does gdb gets this exit code? Any commands inside gdb?
Thanks!
When a program exits, gdb sets the convenience variable $_exitcode to the exit code.
So given:
int main() {
return 23;
}
Running it in gdb, I get:
(gdb) run
Starting program: /tmp/q
[Inferior 1 (process 3677) exited with code 027]
(gdb) print $_exitcode
$1 = 23
It just prints exit code at the end of debug session when the program terminates. Or prints exited normally for 0 exit code. See test debug session for this test program:
#include <stdlib.h>
int main(int argc, char *argv[]) {
return atoi(argv[1]);
}
Debug session:
[ksemenov#NB824RIH ~]$ gdb -q ./a.out
Reading symbols from ./a.out...(no debugging symbols found)...done.
(gdb) r 0
Starting program: /home/ksemenov/a.out 0
Missing separate debuginfos, use: dnf debuginfo-install glibc-2.23.1-10.fc24.x86_64
[Inferior 1 (process 19162) exited normally]
(gdb) r 1
Starting program: /home/ksemenov/a.out 1
[Inferior 1 (process 19166) exited with code 01]
(gdb) r 6
Starting program: /home/ksemenov/a.out 6
[Inferior 1 (process 19167) exited with code 06]
(gdb)
Related
For the first time I use gdb to call the function Test(), it shows gdborig.exe has stopped working.
#include <cstdio>
int a=1;
int Test(){
return ++a;
}
int main(){
printf("%d",Test());
return 0;
}
Then I reboot the cmd, this time it just exit without any warning.
Reading symbols from Test... done.
(gdb) b 7
Breakpoint 1 at Ox401573: file Test.cpp, line 7.
(gdb) r
Starting program: C:\Users\He\Desktop\Test.exe
[New Thread 12420. Ox41ec]
[New Thread 12420. Ox2c68]
Thread 1 hit Breakpoint 1, main () at Test.cpp:7
7 printf("%d", Test()) ;
(gdb) call Test()
The gdb version is gdb-8.1
I have a program in C++ on an Ubuntu machine, that contains several threads, every thread is responsible for big amount of functions and sub functions.
The program runs, but every ~30 minutes the code stops running, I'm trying to understand why. So far I tried to:
Put try-catch all over the code: main and every thread - the program stops running without catching:
try
{
//code
}
catch(const std::exception & e)
{
}
catch(...)
{
}
2.Using strace: When the code stops running, the last lines of the output file are:
nanosleep({0, 10000}, NULL) = 0
nanosleep({0, 10000}, NULL) = 0
nanosleep({0, 10000}, NULL) = 0
nanosleep({0, 10000}, NULL) = 0
nanosleep({0, 10000}, NULL) = 0
nanosleep({0, 10000}, NULL) = 0
nanosleep({0, 10000}, NULL) = 0
nanosleep({0, 10000}, NULL) = 0
nanosleep({0, 10000}, <ptrace(SYSCALL):No such process>
+++ killed by SIGABRT +++
I cannot understand what causes the abortion of the program by killed by SIGABRT message or <ptrace(SYSCALL):No such process>
Using gdb: I put
(gdb) catch throw
(gdb) run
the code starts to run but it seems that the gdb stops running:
Starting program: *****
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7ffff2d6a700 (LWP 13305)]
[Thread 0x7ffff2d6a700 (LWP 13305) exited]
[Inferior 1 (process 13304) exited normally]
(gdb)
If I'm doing something wrong here, I'll be happy to know what is wrong and if not, are there some other ways\tools to trace the problem?
I'm starting to think maybe it something external to the program that causes this issue (?).
Thanks.
Put breakpoints on everything that exits
b exit
b _exit
b __exit
b exit_group
And maybe also kill variants, if you don’t use them elsewhere
b kill
I am using Visual Studio 17 v15.0 and Win 10 Anniversary Update SDK.
I build the following code (basically sample in github repo) with cl /EHsc /O2 /DUNICODE /bigobj /await /std:c++latest, with /MT or MD. It compiles without error.
If I run when `"message.png" is not present in current directory, exception will be thrown, caught and reported with printf, then exit without crashing.
If I run when `"message.png" is present in current directory, "Hello World!" will be printed, then crash for no reason.
Weird thing is If I run it inside GDB debugger, GDB always say the program exits normally (and indeed no crash happen).
GDB output:
[New Thread 1364.0x2324]
[New Thread 1364.0x624]
[New Thread 1364.0x12cc]
[New Thread 1364.0x58c]
[New Thread 1364.0x1134]
[New Thread 1364.0x10d8]
[New Thread 1364.0x18a8]
[New Thread 1364.0x1794]
[New Thread 1364.0x20e8]
[New Thread 1364.0x2204]
[New Thread 1364.0x1030]
[New Thread 1364.0x1474]
Hello world!
[Thread 1364.0x10d8 exited with code 0]
[Thread 1364.0x624 exited with code 0]
[Thread 1364.0x20e8 exited with code 0]
[Thread 1364.0x1794 exited with code 0]
[Thread 1364.0x18a8 exited with code 0]
[Thread 1364.0x58c exited with code 0]
[Thread 1364.0x1134 exited with code 0]
[Thread 1364.0x12cc exited with code 0]
[Thread 1364.0x8d0 exited with code 0]
[Thread 1364.0x2324 exited with code 0]
[Thread 1364.0x1b38 exited with code 0]
[Thread 1364.0x2204 exited with code 0]
[Thread 1364.0x1030 exited with code 0]
[Thread 1364.0x1474 exited with code 0]
[Inferior 1 (process 1364) exited normally]
Code:
#pragma comment(lib, "windowsapp")
#pragma comment(lib, "pathcch")
#include <winrt/Windows.Storage.Streams.h>
#include <winrt/Windows.Graphics.Imaging.h>
#include <winrt/Windows.Media.Ocr.h>
#include <winrt/Windows.Networking.Sockets.h>
#include <pathcch.h>
using namespace winrt;
using namespace std::chrono;
using namespace Windows::Foundation;
using namespace Windows::Storage;
using namespace Windows::Storage::Streams;
using namespace Windows::Graphics::Imaging;
using namespace Windows::Media::Ocr;
hstring MessagePath()
{
wchar_t buffer[1024]{};
GetCurrentDirectory(_countof(buffer), buffer);
check_hresult(PathCchAppendEx(buffer, _countof(buffer), L"message.png", PATHCCH_ALLOW_LONG_PATHS));
return buffer;
}
IAsyncOperation<hstring> AsyncSample()
{
StorageFile file = co_await StorageFile::GetFileFromPathAsync(MessagePath());
IRandomAccessStream stream = co_await file.OpenAsync(FileAccessMode::Read);
BitmapDecoder decoder = co_await BitmapDecoder::CreateAsync(stream);
SoftwareBitmap bitmap = co_await decoder.GetSoftwareBitmapAsync();
OcrEngine engine = OcrEngine::TryCreateFromUserProfileLanguages();
OcrResult result = co_await engine.RecognizeAsync(bitmap);
return result.Text();
}
int main()
{
init_apartment();
try
{
printf("%ls\n", AsyncSample().get().c_str());
}
catch (hresult_error const & e)
{
printf("hresult_error: (0x%8X) %ls\n", e.code(), e.message().c_str());
}
return 0;
}
Turns out hstring returned by AsyncSample().get() is not null terminated, so printf crashes.
try
{
auto ans = AsyncSample().get();
printf("[%u]: ", ans.size());
auto s = ans.c_str();
for (uint32_t i = 0; i < ans.size(); i++) {
printf("%lc", s[i]);
}
putchar('\n');
}
I first asked the question here. Now I encounter the same problem when using clang, hence ask again.
I tried both clang++ 3.8 and 3.9, the command options are "-g -O0".
The gdb version is 7.11.1-0ubuntu1~16.04.
Here is the code:
#include <iostream>
using namespace std;
class D
{
int n;
public:
D(int _n):n(_n){}
void dump(ostream &os);
};
void
D::dump(ostream &os)
{
os << "n=" << n << std::endl;
}
int main() {
D d(200);
std::cout << "hello" << std::endl;
return 0;
}
When it runs to "return 0", call command fails:
(gdb) call d.dump(std::cout)
A syntax error in expression, near `)'.
The same code and same gdb command work fine when compiled with g++ with same option.
Is there a workaround?
It might be because of a verison problem . The program is working fine. I executed it
~/c++practise> g++ stackoverflow1.cpp
~/c++practise> ./a.out
hello
~/c++practise> gdb --version
GNU gdb (GDB) Red Hat Enterprise Linux (7.2-90.el6)
g++ (GCC) 4.4.7 20120313 (Red Hat 4.4.7-17)
Make breakpoint pending on future shared library load? (y or [n]) n
(gdb) b std::cout
"std::cout" is not a function
(gdb) b D::dump(ostream &os)
Breakpoint 1 at 0x400865: file stackoverflow1.cpp, line 15.
(gdb) b main
Breakpoint 2 at 0x4008a2: file stackoverflow1.cpp, line 19.
(gdb) run
Starting program: /home/e1211797/c++practise/outputtrail
Breakpoint 2, main () at stackoverflow1.cpp:19
19 D d(200);
Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.192.el6.x86_64 libgcc-4.4.7-17.el6.x86_64 libstdc++-4.4.7-17.el6.x86_64
(gdb) s
D::D (this=0x7fffffffe0a0, _n=200) at stackoverflow1.cpp:8
8 D(int _n):n(_n){}
(gdb) s
main () at stackoverflow1.cpp:21
21 std::cout << "hello" << std::endl;
(gdb) s
hello
22 return 0;
(gdb) s
23 }
(gdb) s
0x0000003788c1ed1d in __libc_start_main () from /lib64/libc.so.6
(gdb) s
Single stepping until exit from function __libc_start_main,
which has no line number information.
Program exited normally.
(gdb)
I am debugging C++ in gdb 7.1 on Linux.
I have a function a() that is called in many places in the code. I want to set a breakpoint in it, but only if it was called from b(). Is there any way to do it?
Is there any way to do it only if b() was called from c(), and so on ad infinitum?
Update: There is now a better answer to this question: use GDB _is_caller convenience function.
The need you describe comes up quite often, usually in the context of some_utility_fn being called a lot, but you only are interested in the call which comes from some_other_fn.
You could probably script this entire interaction using the new embedded Python support in GDB from CVS trunk.
Without Python, you are limited in what you can do, but the usual technique is to have a disabled breakpoint on a(), and enable it from a command, attached to a breakpoint on b().
Here is an example:
int a(int x)
{
return x + 1;
}
int b()
{
return a(1);
}
int call_a_lots()
{
int i, sum = 0;
for (i = 0; i < 100; i++)
sum += a(i);
}
int main()
{
call_a_lots();
return b();
}
gcc -g t.c
gdb -q ./a.out
Reading symbols from /tmp/a.out...done.
(gdb) break a
Breakpoint 1 at 0x4004cb: file t.c, line 3.
(gdb) disable 1
(gdb) break b
Breakpoint 2 at 0x4004d7: file t.c, line 8.
(gdb) command 2
>silent
>enable 1
>continue
>end
(gdb) run
Breakpoint 1, a (x=1) at t.c:3
3 return x + 1;
(gdb) bt
#0 a (x=1) at t.c:3
#1 0x00000000004004e1 in b () at t.c:8
#2 0x000000000040052c in main () at t.c:21
(gdb) q
Voila: we've stopped on a() called from b(), ignoring previous 100 calls to a().
gdb can handle this directly now without any need for Python. Just do this:
b a if $_caller_is("b")
I have tested this on gdb 7.6 that is already available but it does not work on gdb 7.2 and probably on gdb 7.1:
So this is main.cpp:
int a()
{
int p = 0;
p = p +1;
return p;
}
int b()
{
return a();
}
int c()
{
return a();
}
int main()
{
c();
b();
a();
return 0;
}
Then g++ -g main.cpp
This is my_check.py:
class MyBreakpoint (gdb.Breakpoint):
def stop (self):
if gdb.selected_frame().older().name()=="b":
gdb.execute("bt")
return True
else:
return False
MyBreakpoint("a")
And this is how it works:
4>gdb -q -x my_check.py ./a.out
Reading symbols from /home/a.out...done.
Breakpoint 1 at 0x400540: file main.cpp, line 3.
(gdb) r
Starting program: /home/a.out
#0 a () at main.cpp:3
#1 0x0000000000400559 in b () at main.cpp:10
#2 0x0000000000400574 in main () at main.cpp:21
Breakpoint 1, a () at main.cpp:3
3 int p = 0;
(gdb) c
Continuing.
[Inferior 1 (process 16739) exited normally]
(gdb) quit
A simpler solution than Python scripting is using a temporary breakpoint.
It looks like this:
b ParentFunction
command 1
tb FunctionImInterestedIn
c
end
Every time you break in ParentFunction, you'll set a one-time breakpoint on the function you're actually interested in, then continue running (presumably until you hit that breakpoint).
Since you'll break exactly once on FunctionImInterestedIn, this won't work if FunctionImInterestedIn is called multiple times in the context of ParentFunction and you want to break on each invocation.
not sure how to do it by gdb.
But you can declare global variable like:
bool call_a = false;
and when b calling a
call_a = true;
a();
and set call_a to false when other function call a() or after your breakpoint
then use condition break-point
break [line-number] if call_a == true
An easy one for arm is:
Set the breakpoint in the function you are interested.
break a
Attach an gdb command to that breakpoint.
command 1
up 1
if $lr == 0x12345678
echo match \n
down 1
else
echo no match \n
echo $lr \n
down 1
cont
end
end
When ever you arrive in the function a(), the command temporarily pops up one stack frame thus updating the link register. The callers link register value can then be used continue when the caller is not the execution
path you need.
Enjoy.