即使给出了非剥离版本，GDB 也不显示剥离核心文件的符号

问题描述 投票：0回答：1

我通过经典的配置、制作、安装来构建程序。几个月后，程序崩溃了。我仍然有源代码和未剥离的可执行文件所在的构建目录。从那里，我像这样调用 gdb：

530-north:courier$ gdb -q --core /tmp/core_epoch\=1667475742_pid\=23653_file\=\!usr\!local\!libexec\!courier\!courierd courierd
Reading symbols from courierd...
[New LWP 23653]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `/usr/local/libexec/courier/courierd'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x0000561e841e5afd in msgq::completed(drvinfo&, unsigned long) ()
(gdb) info args
No symbol table info available.

使用 

bt
，我可以看到两个函数之间的一长串调用：

#0  0x0000561e841e5afd in msgq::completed(drvinfo&, unsigned long) ()
#1  0x0000561e841e609a in msgq::startdelivery(drvinfo*, delinfo*) ()
#2  0x0000561e841e5bd8 in msgq::completed(drvinfo&, unsigned long) ()
#3  0x0000561e841e609a in msgq::startdelivery(drvinfo*, delinfo*) ()
#4  0x0000561e841e5bd8 in msgq::completed(drvinfo&, unsigned long) ()
...
#204 0x0000561e841e5a17 in msgq::completed(drvinfo&, unsigned long) ()
#205 0x0000561e841e609a in msgq::startdelivery(drvinfo*, delinfo*) ()
#206 0x0000561e841e5a17 in msgq::completed(drvinfo&, unsigned long) ()
#207 0x0000561e841e70fe in courierbmain() ()
#208 0x0000561e841dd030 in main ()

每两次调用都会将堆栈推进 0x110，总共约 27Kb，这远小于正在运行的进程分配的 132Kb 堆栈，因此这不是堆栈溢出。 SIGSEGV 可能来自空指针或其他任何东西。为什么gdb不指向它？这是 GNU gdb (Debian 10.1-1.7) 10.1.90.20210103-git，顺便说一句。

如果我省略 gdb 的最后一个参数，

bt
不会显示函数名称。我搞砸了编译吗？在 config.log 上，我看到我有 
'CFLAGS= -march=nocona -O2 -g' 'LDFLAGS= -march=nocona -O2' 'CXXFLAGS= -march=nocona -O2 -std=c++11'
。源文件是C++。也许我错过了一些
-g
？然而，一些符号在那里......

c++11 gdb coredump
1个回答
1
投票

为什么gdb不指向它？

因为你还没有使用适当的调试信息编译你的程序。

您必须在程序集级别调试此崩溃。从 

disasemble $pc
和 
info registers
开始。

源文件是C++。也许我错过了一些-gs？

是的：您的 

CXXFLAGS
没有 
-g
。

但是，还是有一些符号...

在 UNIX 系统（与 Windows 不同）上，即使没有 

-g
，函数名称（符号）也会存在（默认情况下）。这里并不矛盾。

更新：

但是，如果我不传递非剥离文件作为参数，则不会显示函数名称。

是：

strip
删除符号和调试信息。

您可以通过一个简单的测试来观察这一点：

// t.cc
#include <cstdlib>

struct S {
  void fn() { abort(); }
};

int main()
{
  S().fn();
}

首先让我们看看当二进制文件正确构建用于调试时它是如何工作的：

g++ -g t.cc -o a.out && strip ./a.out -o a.out.stripped &&
./a.out.stripped; gdb -q --batch -ex where ./a.out core
Aborted (core dumped)
...
warning: core file may not match specified executable file.
[New LWP 476070]
Core was generated by `./a.out.stripped'.
Program terminated with signal SIGABRT, Aborted.
#0  __pthread_kill_implementation (threadid=<optimized out>, signo=6, no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44
44      ./nptl/pthread_kill.c: No such file or directory.
#0  __pthread_kill_implementation (threadid=<optimized out>, signo=6, no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44
#1  0x00007f12444895df in __pthread_kill_internal (signo=<optimized out>, threadid=<optimized out>) at ./nptl/pthread_kill.c:89
#2  __GI___pthread_kill (threadid=<optimized out>, signo=<optimized out>) at ./nptl/pthread_kill.c:89
#3  0x00007f12445f5e70 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#4  0x00007f1244428469 in __GI_abort () at ./stdlib/abort.c:79
#5  0x000055de28a24165 in S::fn (this=0x7ffcd0d1d80f) at t.cc:4
#6  0x000055de28a2414d in main () at t.cc:9

注意文件/行信息和函数名称的存在。如果我们使用精简版本，则两者都不存在：

ore was generated by `./a.out.stripped'.
Program terminated with signal SIGABRT, Aborted.
#0  __pthread_kill_implementation (threadid=<optimized out>, signo=6, no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44
44      ./nptl/pthread_kill.c: No such file or directory.
#0  __pthread_kill_implementation (threadid=<optimized out>, signo=6, no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44
#1  0x00007f12444895df in __pthread_kill_internal (signo=<optimized out>, threadid=<optimized out>) at ./nptl/pthread_kill.c:89
#2  __GI___pthread_kill (threadid=<optimized out>, signo=<optimized out>) at ./nptl/pthread_kill.c:89
#3  0x00007f12445f5e70 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#4  0x00007f1244428469 in __GI_abort () at ./stdlib/abort.c:79
#5  0x000055de28a24165 in ?? ()
#6  0x000055de28a2414d in ?? ()
#7  0x00007f124442920a in __libc_start_call_main (main=main@entry=0x55de28a24139, argc=argc@entry=1, argv=argv@entry=0x7ffcd0d1d928) at ../sysdeps/nptl/libc_start_call_main.h:58
#8  0x00007f12444292bc in __libc_start_main_impl (main=0x55de28a24139, argc=1, argv=0x7ffcd0d1d928, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7ffcd0d1d918) at ../csu/libc-start.c:389
#9  0x000055de28a24071 in ?? ()

现在让我们重复一下错误构建的二进制文件（这就是你所拥有的）：

g++ t.cc -o b.out && strip ./b.out -o b.out.stripped &&
./b.out.stripped; gdb -q --batch -ex where ./b.out core
Aborted (core dumped)
...
warning: core file may not match specified executable file.
[New LWP 478614]
Core was generated by `./b.out.stripped'.
Program terminated with signal SIGABRT, Aborted.
#0  __pthread_kill_implementation (threadid=<optimized out>, signo=6, no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44
44      ./nptl/pthread_kill.c: No such file or directory.
#0  __pthread_kill_implementation (threadid=<optimized out>, signo=6, no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44
#1  0x00007f21a0a895df in __pthread_kill_internal (signo=<optimized out>, threadid=<optimized out>) at ./nptl/pthread_kill.c:89
#2  __GI___pthread_kill (threadid=<optimized out>, signo=<optimized out>) at ./nptl/pthread_kill.c:89
#3  0x00007f21a0bf5e70 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#4  0x00007f21a0a28469 in __GI_abort () at ./stdlib/abort.c:79
#5  0x000056049b052165 in S::fn() ()
#6  0x000056049b05214d in main ()

注意函数名称的存在（

S::fn()
、
main
），但缺少文件/行/参数信息。这与您观察到的结果相符。

如果您使用 

b.out.stripped
再次尝试，您将得到与上次使用 
a.out.stripped
运行相同的结果：

Core was generated by `./b.out.stripped'.
Program terminated with signal SIGABRT, Aborted.
#0  __pthread_kill_implementation (threadid=<optimized out>, signo=6, no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44
44      ./nptl/pthread_kill.c: No such file or directory.
#0  __pthread_kill_implementation (threadid=<optimized out>, signo=6, no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44
#1  0x00007f21a0a895df in __pthread_kill_internal (signo=<optimized out>, threadid=<optimized out>) at ./nptl/pthread_kill.c:89
#2  __GI___pthread_kill (threadid=<optimized out>, signo=<optimized out>) at ./nptl/pthread_kill.c:89
#3  0x00007f21a0bf5e70 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#4  0x00007f21a0a28469 in __GI_abort () at ./stdlib/abort.c:79
#5  0x000056049b052165 in ?? ()
#6  0x000056049b05214d in ?? ()
#7  0x00007f21a0a2920a in __libc_start_call_main (main=main@entry=0x56049b052139, argc=argc@entry=1, argv=argv@entry=0x7fff3554bc78) at ../sysdeps/nptl/libc_start_call_main.h:58
#8  0x00007f21a0a292bc in __libc_start_main_impl (main=0x56049b052139, argc=1, argv=0x7fff3554bc78, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fff3554bc68) at ../csu/libc-start.c:389
#9  0x000056049b052071 in ?? ()

此外，readelf --debug-dump=info courierd 显示了很多版本 4 的内容。

是的，如果你运行

readelf --debug-dump b.out
，你可以观察到很多来自
crt0.o
、
crtbegin.o
等的DWARF4内容（取决于你的GCC和GLIBC是如何构建的）。

如果您链接了 

.c
文件，这些文件也将包含 DWARF4 调试信息，因为您的 
CFLAGS
do 包含 
-g
。

但是任何 DWARF4 的东西都不会来自定义 

msgq::completed
的地方。

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