linux 当一个程序的核心转储文件有命令行参数时,我如何用GDB分析它?

new9mtju  于 2022-11-28  发布在  Linux
关注(0)|答案(9)|浏览(146)

我的程序是这样运行的:

exe -p param1 -i param2 -o param3

它崩溃并生成一个核心转储文件core.pid
我想通过以下方式分析核心转储文件

gdb ./exe -p param1 -i param2 -o param3 core.pid

但是GDB将EXE文件的参数识别为GDB的输入。
在这种情况下,如何分析核心转储文件?

jecbmhm3

jecbmhm31#

You can use the core with GDB in many ways, but passing parameters which is to be passed to the executable to GDB is not the way to use the core file. This could also be the reason you got that error. You can use the core file in the following ways:
gdb <executable> <core-file> or gdb <executable> -c <core-file> or

gdb <executable>
...
(gdb) core <core-file>

When using the core file you don't have to pass arguments. The crash scenario is shown in GDB (checked with GDB version 7.1 on Ubuntu).
For example:

$ ./crash -p param1 -o param2
Segmentation fault (core dumped)
$ gdb ./crash core
GNU gdb (GDB) 7.1-ubuntu
...
Core was generated by `./crash -p param1 -o param2'. <<<<< See this line shows crash scenario
Program terminated with signal 11, Segmentation fault.
#0  __strlen_ia32 () at ../sysdeps/i386/i686/multiarch/../../i586/strlen.S:99
99    ../sysdeps/i386/i686/multiarch/../../i586/strlen.S: No such file or directory.
    in ../sysdeps/i386/i686/multiarch/../../i586/strlen.S
(gdb)

If you want to pass parameters to the executable to be debugged in GDB, use --args .
For example:

$ gdb --args ./crash -p param1 -o param2
GNU gdb (GDB) 7.1-ubuntu
...
(gdb) r
Starting program: /home/@@@@/crash -p param1 -o param2

Program received signal SIGSEGV, Segmentation fault.
__strlen_ia32 () at ../sysdeps/i386/i686/multiarch/../../i586/strlen.S:99
99    ../sysdeps/i386/i686/multiarch/../../i586/strlen.S: No such file or directory.
    in ../sysdeps/i386/i686/multiarch/../../i586/strlen.S
(gdb)

Man pages will be helpful to see other GDB options.
Most useful commands are:

  • bt (backtrace)
  • info locals (show values of local variables)
  • info registers (show values of CPU registers)
  • frame X (change to stack frame X)
  • up and down (navigate in the stack frame (call chain))
bakd9h0s

bakd9h0s2#

GDB的简单用法,调试核心转储文件:

gdb <executable_path> <coredump_file_path>

A coredump file for a "process" gets created as a "core.pid" file.
进入GDB提示符后(在执行上述命令时),键入:

...
(gdb) where

这将为您提供堆栈的信息,您可以在其中分析崩溃/故障的原因。**其他命令,**用于相同的目的是:

...
(gdb) bt full

这和上面一样,按照惯例,它列出了整个堆栈信息(最终导致崩溃的位置)。

km0tfn4u

km0tfn4u3#

objdump + gdb minimal runnable example

TL;DR:

  • GDB can be used to find failing line, previously mentioned at: How do I analyze a program's core dump file with GDB when it has command-line parameters?
  • the core file contains the CLI arguments, no need to pass them again
  • objdump -s core can be used to dump memory in bulk

Now for the full educational test setup:
main.c

#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int myfunc(int i) {
    *(int*)(NULL) = i; /* line 7 */
    return i - 1;
}

int main(int argc, char **argv) {
    /* Setup some memory. */
    char data_ptr[] = "string in data segment";
    char *mmap_ptr;
    char *text_ptr = "string in text segment";
    (void)argv;
    mmap_ptr = (char *)malloc(sizeof(data_ptr) + 1);
    strcpy(mmap_ptr, data_ptr);
    mmap_ptr[10] = 'm';
    mmap_ptr[11] = 'm';
    mmap_ptr[12] = 'a';
    mmap_ptr[13] = 'p';
    printf("text addr: %p\n", text_ptr);
    printf("data addr: %p\n", data_ptr);
    printf("mmap addr: %p\n", mmap_ptr);

    /* Call a function to prepare a stack trace. */
    return myfunc(argc);
}

Compile, and run to generate core:

gcc -ggdb3 -std=c99 -Wall -Wextra -pedantic -o main.out main.c
ulimit -c unlimited
rm -f core
./main.out

On Ubuntu 22.04, you also need to fight against apport to get your core file: https://askubuntu.com/questions/1349047/where-do-i-find-core-dump-files-and-how-do-i-view-and-analyze-the-backtrace-st/1442665#1442665 e.g. with:

echo 'core' | sudo tee /proc/sys/kernel/core_pattern

and your core is now named as:

core.<pid>

Program output:

text addr: 0x4007d4
data addr: 0x7ffec6739220
mmap addr: 0x1612010
Segmentation fault (core dumped)

GDB points us to the exact line where the segfault happened, which is what most users want while debugging:

gdb -q -nh main.out core

then:

Reading symbols from main.out...done.
[New LWP 27479]
Core was generated by `./main.out'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x0000000000400635 in myfunc (i=1) at main.c:7
7           *(int*)(NULL) = i;
(gdb) bt
#0  0x0000000000400635 in myfunc (i=1) at main.c:7
#1  0x000000000040072b in main (argc=1, argv=0x7ffec6739328) at main.c:28
(gdb) f 1
#1  0x000000000040072b in main (argc=1, argv=0x7ffec6739328) at main.c:28
28          return myfunc(argc);
(gdb) p argc
$1 = 1

which points us directly to the buggy line 7.
As you can see from the example, you are now able to inspect program memory at the time of crash to try and determine the cause of failure, the process virtual memory is entirely contained in the core file.

CLI arguments are stored in the core file and don't need to be passed again

To answer the specific CLI argument questions, we see that if we change the cli arguments e.g. with:

rm -f core
./main.out 1 2

then this does get reflected in the previous bactrace without any changes in our commands:

Reading symbols from main.out...done.
[New LWP 21838]
Core was generated by `./main.out 1 2'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x0000564583cf2759 in myfunc (i=3) at main.c:7
7           *(int*)(NULL) = i; /* line 7 */
(gdb) bt
#0  0x0000564583cf2759 in myfunc (i=3) at main.c:7
#1  0x0000564583cf2858 in main (argc=3, argv=0x7ffcca4effa8) at main.c:2

So note how now argc=3 . Therefore this must mean that the core file stores that information. I'm guessing it just stores it as the arguments of main , just like it stores the arguments of any other functions.
This makes sense if you consider that the core dump must be storing the entire memory and register state of the program, and so it has all the information needed to determine the value of function arguments on the current stack.
Less obvious is how to inspect the environment variables: How to get environment variable from a core dump Environment variables are also present in memory so the objdump does contain that information, but I'm not sure how to list all of them in one go conveniently, one by one as follows did work on my tests though:

p __environ[0]

Binutils analysis

By using binutils tools like readelf and objdump , we can bulk dump information contained in the core file such as the memory state.
Most/all of it must also be visible through GDB, but those binutils tools offer a more bulk approach which is convenient for certain use cases, while GDB is more convenient for a more interactive exploration.
First:

file core

tells us that the core file is actually an ELF file:

core: ELF 64-bit LSB core file x86-64, version 1 (SYSV), SVR4-style, from './main.out'

which is why we are able to inspect it more directly with usual binutils tools.
A quick look at the ELF standard shows that there is actually an ELF type dedicated to it:

Elf32_Ehd.e_type == ET_CORE

Further format information can be found at:

man 5 core

Then:

readelf -Wa core

gives some hints about the file structure. Memory appears to be contained in regular program headers:

Program Headers:
  Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
  NOTE           0x000468 0x0000000000000000 0x0000000000000000 0x000b9c 0x000000     0
  LOAD           0x002000 0x0000000000400000 0x0000000000000000 0x001000 0x001000 R E 0x1000
  LOAD           0x003000 0x0000000000600000 0x0000000000000000 0x001000 0x001000 R   0x1000
  LOAD           0x004000 0x0000000000601000 0x0000000000000000 0x001000 0x001000 RW  0x1000

and there is some more metadata present in a notes area, notably prstatus contains the PC:

Displaying notes found at file offset 0x00000468 with length 0x00000b9c:
  Owner                 Data size       Description
  CORE                 0x00000150       NT_PRSTATUS (prstatus structure)
  CORE                 0x00000088       NT_PRPSINFO (prpsinfo structure)
  CORE                 0x00000080       NT_SIGINFO (siginfo_t data)
  CORE                 0x00000130       NT_AUXV (auxiliary vector)
  CORE                 0x00000246       NT_FILE (mapped files)
    Page size: 4096
                 Start                 End         Page Offset
    0x0000000000400000  0x0000000000401000  0x0000000000000000
        /home/ciro/test/main.out
    0x0000000000600000  0x0000000000601000  0x0000000000000000
        /home/ciro/test/main.out
    0x0000000000601000  0x0000000000602000  0x0000000000000001
        /home/ciro/test/main.out
    0x00007f8d939ee000  0x00007f8d93bae000  0x0000000000000000
        /lib/x86_64-linux-gnu/libc-2.23.so
    0x00007f8d93bae000  0x00007f8d93dae000  0x00000000000001c0
        /lib/x86_64-linux-gnu/libc-2.23.so
    0x00007f8d93dae000  0x00007f8d93db2000  0x00000000000001c0
        /lib/x86_64-linux-gnu/libc-2.23.so
    0x00007f8d93db2000  0x00007f8d93db4000  0x00000000000001c4
        /lib/x86_64-linux-gnu/libc-2.23.so
    0x00007f8d93db8000  0x00007f8d93dde000  0x0000000000000000
        /lib/x86_64-linux-gnu/ld-2.23.so
    0x00007f8d93fdd000  0x00007f8d93fde000  0x0000000000000025
        /lib/x86_64-linux-gnu/ld-2.23.so
    0x00007f8d93fde000  0x00007f8d93fdf000  0x0000000000000026
        /lib/x86_64-linux-gnu/ld-2.23.so
  CORE                 0x00000200       NT_FPREGSET (floating point registers)
  LINUX                0x00000340       NT_X86_XSTATE (x86 XSAVE extended state)

objdump can easily dump all memory with:

objdump -s core

which contains:

Contents of section load1:

 4007d0 01000200 73747269 6e672069 6e207465  ....string in te
 4007e0 78742073 65676d65 6e740074 65787420  xt segment.text 

Contents of section load15:

 7ffec6739220 73747269 6e672069 6e206461 74612073  string in data s
 7ffec6739230 65676d65 6e740000 00a8677b 9c6778cd  egment....g{.gx.

Contents of section load4:

 1612010 73747269 6e672069 6e206d6d 61702073  string in mmap s
 1612020 65676d65 6e740000 11040000 00000000  egment..........

which matches exactly with the stdout value in our run.
This was tested on Ubuntu 16.04 amd64, GCC 6.4.0, and binutils 2.26.1.

Mozilla rr reverse debugging as the ultimate "core file"

Core files allow you to inspect the stack at break.
But in general what you really need to do is to go back in time to further decide the root failure cause.
The amazing Mozilla rr allows you to do that, at the cost of a larger trace file, and a slight performance hit.
Example at: How does reverse debugging work?

vybvopom

vybvopom4#

跳过参数即可。GDB不需要这些参数:

gdb ./exe core.pid
dced5bon

dced5bon5#

来自RMS的GDB调试器教程:

prompt > myprogram
Segmentation fault (core dumped)
prompt > gdb myprogram
...
(gdb) core core.pid
...

确保您的文件确实是core图像--使用file检查它。

gupuwyp2

gupuwyp26#

一种稍微不同的方法可以让你完全跳过GDB。如果你只需要一个回溯,Linux专用的实用程序'catchsegv'将捕获SIGSEGV并显示一个回溯。

rjee0c15

rjee0c157#

可执行文件是否有参数并不重要。要在任何带有生成的核心文件的二进制文件上运行GDB,语法如下。

Syntax:
gdb <binary name> <generated core file>
Eg:
gdb l3_entity 6290-corefile

让我举下面的例子来更好地理解。

bash-4.1$ **gdb l3_entity 6290-corefile**

**Core was generated** by `/dir1/dir2/dir3/l3_entity **Program terminated with signal SIGABRT, Aborted.**
#0
#1
#2
#3
#4
#5
#6
#7
#8
#9
#10
(gdb)

从上面的输出中,你可以猜出一些关于核心的东西,不管它是NULL访问、SIGABORT等等。
这些数字#0到#10是GDB的堆栈帧。这些堆栈帧不是你的二进制。在上面的0 - 10帧中,如果你怀疑有什么不对的地方,选择那个帧

(gdb) frame 8

现在来看看更多的细节:

(gdb) list +

要进一步调查此问题,您可以及时在此处打印可疑的变量值。

(gdb) print thread_name
tf7tbtn2

tf7tbtn28#

我只是使用coredumpctl debug(在Fedora 32上),它给了我一个GDB控制台来调试我最近的核心转储。

raogr8fs

raogr8fs9#

Simply type the command:

$ gdb <Binary> <codeDump>

Or

$ gdb <binary>

$ gdb) core <coreDump>

There isn't any need to provide any command line argument. The code dump generated due to an earlier exercise.

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