gdb調試單獨的debuginfo文件詳情 - linux,gdb,調試,調試工具,調試技巧 viyon 動態日志

gdb調試單獨的debug文件

2023.11.26

背景

Debug和Release區別

實際上，Debug 和 Release 並沒有本質的界限，人為的區別，沒有特殊的規定。他們只是一組編譯選項的集合，編譯器只是按照預定的選項行動。事實上，我們甚至可以修改這些選項，從而得到優化過的調試版本或是帶跟蹤語句的發佈版本。約定俗成的區別是：

Debug通常稱為調試版本，它包含調試信息，並且不作任何優化，便於程序員調試程序。

Release 稱為發佈版本，它往往是進行了各種優化，使得程序在代碼大小和運行速度上都是最優的，以便用户很好地使用。約定俗成的是release版本不帶調試信息。

不同的軟件有自己不同的選擇。有些軟件會在release版本和debug版本之外，根據自己的需要，出別的版本，如QT分為debug、release、profile版本：

Debug通常稱為調試版本，它包含調試信息，並且不作任何優化，便於程序員調試程序。

Release 稱為發佈版本，它往往是進行了各種優化，使得程序在代碼大小和運行速度上都是最優的，以便用户很好地使用。

profile則是在這兩種之中取一個平衡,兼顧性能和調試, 可以類似的看做是性能更優但是又方便調試的版本。

沒有對錯，也沒有是否最優，看自己的目的，根據自己的目的進行取捨，平衡利弊後，使用一個最優的做法。比如有些軟件可能為了在發佈後調試方便，在添加調試信息的同時，也會添加優化選項進行優化，從而求得一個平衡。有些軟件考慮發佈時攜帶調試信息會讓發佈包變得非常大，不利於網絡分發，就會在發佈時去掉調試信息。

發佈了Release版本後，出問題時定位問題的常用做法

Release版本確實比debug版本在運行速度及體積大小上有一定的優勢，不過如果發佈後的程序出現問題，對於定位問題的人員來説，就比較痛苦了，畢竟沒有調試信息很不方便。為了解決這個問題，linux下的程序一般會有獨立的debuginfo包，這個debuginfo包是和release包一一對應的，當release版本的程序出現問題時，將debuginfo包安裝後，即可像debug版本一樣進行調試。如ls命令，在gdb的時候，如果沒有調試信息，會提示進行安裝，我的操作系統是fedora，有如下提示：

[zy@fedora debuginfo]$ gdb /usr/bin/ls
GNU gdb (Fedora Linux) 13.2-10.fc39
Reading symbols from /usr/bin/ls...
This GDB supports auto-downloading debuginfo from the following URLs:
  <https://debuginfod.fedoraproject.org/>
Enable debuginfod for this session? (y or [n]) n
Debuginfod has been disabled.
To make this setting permanent, add 'set debuginfod enabled off' to .gdbinit.
Reading symbols from .gnu_debugdata for /usr/bin/ls...
(No debugging symbols found in .gnu_debugdata for /usr/bin/ls)
Missing separate debuginfos, use: dnf debuginfo-install coreutils-9.3-4.fc39.x86_64
(gdb) quit

可以看到，gdb提示使用dnf debuginfo-install coreutils-9.3-4.fc39.x86_64命令安裝debuginfo包。安裝完後再gdb，就可以看到已經讀取到符號信息了，如下所示：

[root@fedora debug]# dnf debuginfo-install coreutils
[zy@fedora debuginfo]$ gdb --args /usr/bin/ls .
GNU gdb (Fedora Linux) 13.2-10.fc39
Reading symbols from /usr/bin/ls...
Reading symbols from /usr/lib/debug/usr/bin/ls-9.3-4.fc39.x86_64.debug...[zy@fedora debuginfo]$ gdb --args /usr/bin/ls .
GNU gdb (Fedora Linux) 13.2-10.fc39

如何製作單獨的debuginfo文件

linux下可以通過objcopy命令分離出單獨的debuginfo包,比如一個a.out程序，可以通過如下命令得到deuginfo包

objcopy --only-keep-debug ./a.out a.out.debug
objcopy --strip-debug ./a.out
objcopy --add-gnu-debuglink=a.out.debug ./a.out

objcopy的--only-keep-debug選項，將debug信息分離到一個單獨的文件中。--strip-debug選項將debug信息從a.out中刪除。--add-gnu-debuglink選項將a.out和前面生成的a.out.debug文件關聯起來，這一步很重要，如果沒有這一步，則在gdb調試的時候會找不到調試信息。

這只是其中一種方法，還有一種方法是在編譯時生成build-id，將build-id信息放到編譯後的文件中。本文不介紹此種方式。

gdb調試單獨debuginfo文件的原理介紹

先看一個小例子，使用的gcc版本及gdb版本如下：

[zy@fedora debuginfo]$ gcc --version
gcc (GCC) 13.2.1 20231011 (Red Hat 13.2.1-4)
Copyright © 2023 Free Software Foundation, Inc.
[zy@fedora debuginfo]$ gdb --version
GNU gdb (Fedora Linux) 13.2-10.fc39
Copyright (C) 2023 Free Software Foundation, Inc.

以下是代碼結構及具體的代碼內容：

[zy@fedora gdb_test]$ ls
liba.c  liba.h  main.c
[zy@fedora gdb_test]$ cat liba.c 
#include <stdio.h>
#include <stdlib.h>

int liba_func(int a, int b)
{
    int sum = 0;

    sum = a + b;
    printf("%d + %d = %d.\n", a, b, sum);

    return 0;
}
[zy@fedora gdb_test]$ cat liba.h
#ifndef __LIBA_FUNC__
#define __LIBA_FUNC__
int liba_func(int a, int b);
#endif
[zy@fedora gdb_test]$ cat main.c 
#include <stdio.h>
#include <stdlib.h>
#include "liba.h"

int main()
{
    printf("hello, this is main.\n");
    liba_func(1, 2);
    return 0;
}

[zy@fedora gdb_test]$export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:.

如何添加調試信息到目標文件

當不加任何編譯參數，直接gdb運行的時候，發現設置斷點後，看不到調試信息，如下所示：

[zy@fedora gdb_test]$  gcc liba.c -fpic -shared  -o liba.so
[zy@fedora gdb_test]$ gcc main.c -L. -I. -la  -o test
[zy@fedora gdb_test]$ gdb ./test 
To make this setting permanent, add 'set debuginfod enabled off' to .gdbinit.
(No debugging symbols found in ./test)
(gdb) b main
Breakpoint 1 at 0x40113a
(gdb) b liba_func
Breakpoint 2 at 0x401030
(gdb) run
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Breakpoint 1, 0x000000000040113a in main ()
Missing separate debuginfos, use: dnf debuginfo-install glibc-2.38-10.fc39.x86_64
(gdb) n
Single stepping until exit from function main,
which has no line number information.
main_sum = 90.

Breakpoint 2, 0x00007ffff7fbd10d in liba_func () from liba.so
(gdb) n
Single stepping until exit from function liba_func,
which has no line number information.
1 + 2 = 3.
sum = 4.
0x000000000040118c in main ()
(gdb) n
Single stepping until exit from function main,
which has no line number information.

而加了-g選項後，再用gdb調試的時候，可以看到具體的調試信息，如下所示：

[zy@fedora gdb_test]$  gcc liba.c -fpic -shared -g -o liba.so
[zy@fedora gdb_test]$ gcc main.c -L. -I. -la -g  -o test
[zy@fedora gdb_test]$ gdb ./test
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./test...
(gdb) b main
Breakpoint 1 at 0x40113e: file main.c, line 7.
(gdb) b liba_func
Breakpoint 2 at 0x401030
(gdb) run
Breakpoint 1, main () at main.c:7
7        int main_a = 3;
Missing separate debuginfos, use: dnf debuginfo-install glibc-2.38-10.fc39.x86_64
(gdb) n
8        int main_b = 5;
(gdb) c
Continuing.
main_sum = 90.

Breakpoint 2, liba_func (a=1, b=2) at liba.c:6
6        int sum = 0;
(gdb) n
8        sum = a + b;
(gdb) n
9        printf("%d + %d = %d.\n", a, b, sum);
(gdb) n
1 + 2 = 3.
11        a = a * a;

和看不到調試信息的編譯選項相比，多加了-g編譯選項，查看編譯後的文件，發現多了很多debug相關的segment，如下所示：

[zy@fedora gdb_test]$  gcc liba.c -fpic -shared  -o liba.so
[zy@fedora gdb_test]$ readelf -S liba.so |grep debug
[zy@fedora gdb_test]$  gcc liba.c -fpic -shared -g -o liba.so
[zy@fedora gdb_test]$ readelf -S liba.so |grep debug
  [26] .debug_aranges    PROGBITS         0000000000000000  00003160
  [27] .debug_info       PROGBITS         0000000000000000  00003190
  [28] .debug_abbrev     PROGBITS         0000000000000000  00003273
  [29] .debug_line       PROGBITS         0000000000000000  0000330f
  [30] .debug_str        PROGBITS         0000000000000000  0000337a
  [31] .debug_line_str   PROGBITS         0000000000000000  0000342c

是否包含調試信息，關鍵在於編譯時是否添加-g選項。添加了-g選項後，編譯出來的文件中帶有很多debug相關的段。可以將這些debug信息進行清除，如下所示：

[zy@fedora gdb_test]$  gcc liba.c -fpic -shared -g -o liba.so
[zy@fedora gdb_test]$ file liba.so 
liba.so: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, BuildID[sha1]=cc2b549427fb52d590a07ad72efec99085b9a877, with debug_info, not stripped
[zy@fedora gdb_test]$ readelf -S liba.so |grep debug
  [26] .debug_aranges    PROGBITS         0000000000000000  00003160
  [27] .debug_info       PROGBITS         0000000000000000  00003190
  [28] .debug_abbrev     PROGBITS         0000000000000000  00003273
  [29] .debug_line       PROGBITS         0000000000000000  0000330f
  [30] .debug_str        PROGBITS         0000000000000000  0000337a
  [31] .debug_line_str   PROGBITS         0000000000000000  0000342c
[zy@fedora gdb_test]$ readelf -S liba.so |grep sym
  [ 4] .dynsym           DYNSYM           0000000000000328  00000328
  [32] .symtab           SYMTAB           0000000000000000  00003490
[zy@fedora gdb_test]$ strip -s liba.so 
[zy@fedora gdb_test]$ file liba.so 
liba.so: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, BuildID[sha1]=cc2b549427fb52d590a07ad72efec99085b9a877, stripped
[zy@fedora gdb_test]$ readelf -S liba.so |grep debug
[zy@fedora gdb_test]$ readelf -S liba.so |grep sym
  [ 4] .dynsym           DYNSYM           0000000000000328  00000328

清除後，在編譯後的文件中就看不到debug相關的段了。文件大小也比之前有所減少，如下所示：

[zy@fedora gdb_test]$  gcc liba.c -fpic -shared  -o liba.so
[zy@fedora gdb_test]$ ll liba.so
-rwxr-xr-x. 1 zy zy 15800 11月15日 22:35 liba.so
[zy@fedora gdb_test]$  gcc liba.c -fpic -shared -g  -o liba.so
[zy@fedora gdb_test]$ ll liba.so
-rwxr-xr-x. 1 zy zy 17080 11月15日 22:35 liba.so
[zy@fedora gdb_test]$ strip -s liba.so 
[zy@fedora gdb_test]$ ll liba.so
-rwxr-xr-x. 1 zy zy 14392 11月15日 22:35 liba.so

使用objcopy命令分離出單獨的debuginfo文件

前面已經介紹過，使用objcopy命令可以將debug信息分離到單獨的文件中，如下所示：

[zy@fedora gdb_test]$ gcc main.c -L. -I. -la -g -o test
[zy@fedora gdb_test]$ ls
liba.c  liba.h  liba.so  main.c  test
[zy@fedora gdb_test]$ objcopy --only-keep-debug ./liba.so liba.so.debug
[zy@fedora gdb_test]$ objcopy --strip-all liba.so
liba.so        liba.so.debug  
[zy@fedora gdb_test]$ objcopy --strip-all liba.so
[zy@fedora gdb_test]$ ls
liba.c  liba.h  liba.so  liba.so.debug  main.c  test

如果不使用objcopy --add-gnu-debuglink=liba.so.debug liba.so命令將分離出的debuginfo文件和原始程序關聯起來，在使用gdb調試的時候，發現無法看到調試信息，如下所示：

[zy@fedora gdb_test]$ gdb ./test
Enable debuginfod for this session? (y or [n]) n
Debuginfod has been disabled.
To make this setting permanent, add 'set debuginfod enabled off' to .gdbinit.
(No debugging symbols found in ./test)
(gdb) b main
Function "main" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (main) pending.
(gdb) b liba_func
Breakpoint 2 at 0x401030
(gdb) run
Starting program: /home/zy/debuginfo/test 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
main_sum = 90.

Breakpoint 2, 0x00007ffff7fbd10d in liba_func () from liba.so
Missing separate debuginfos, use: dnf debuginfo-install glibc-2.38-10.fc39.x86_64
(gdb) n
Single stepping until exit from function liba_func,
which has no line number information.
1 + 2 = 3.
sum = 4.
0x000000000040118c in ?? ()
(gdb) n
Cannot find bounds of current function

使用了objcopy --add-gnu-debuglink命令之後,可以看到具體的調試信息了，如下所示：

[zy@fedora gdb_test]$ objcopy --add-gnu-debuglink=liba.so.debug liba.so
[zy@fedora gdb_test]$ objcopy --add-gnu-debuglink=test.debug test
[zy@fedora gdb_test]$ gdb ./test
Reading symbols from ./test...
Reading symbols from /home/zy/debuginfo/test.debug...
(gdb) b main
Breakpoint 1 at 0x40113e: file main.c, line 7.
(gdb) b liba_func
Breakpoint 2 at 0x401030
(gdb) run
Using host libthread_db library "/lib64/libthread_db.so.1".

Breakpoint 1, main () at main.c:7
7        int main_a = 3;
Missing separate debuginfos, use: dnf debuginfo-install glibc-2.38-10.fc39.x86_64
(gdb) n
8        int main_b = 5;
(gdb) n
9        int main_sum = 0;
(gdb) n
11        main_a = main_a * main_a;
(gdb) c
Continuing.
main_sum = 90.

Breakpoint 2, liba_func (a=1, b=2) at liba.c:6
6        int sum = 0;
(gdb) n
8        sum = a + b;
(gdb) n
9        printf("%d + %d = %d.\n", a, b, sum);
(gdb) n
1 + 2 = 3.
11        a = a * a;
(gdb) n
12        b = b * 2;
(gdb)

為什麼一定要使用--add-gnu-debuglink選項後才能看到調試信息呢？因為分離出單獨的debuginfo文件後，文件名稱是可以隨意起的，gdb在調試程序的時候，怎麼知道去哪個文件中找調試信息呢？這就需要在原來的程序中添加一些線索才行，這個線索就是調試文件的名稱。其實現原理是在程序中有一個專門的段，叫做.gnu_debuglink段，用以記錄debuginfo文件相關的信息，主要是文件名稱和該文件的CRC校驗碼。如下所示：

[zy@fedora gdb_test]$ readelf -S liba.so|grep debug
  [26] .gnu_debuglink    PROGBITS         0000000000000000  00003160
[zy@fedora gdb_test]$ objdump -s -j .gnu_debuglink liba.so

liba.so：     文件格式 elf64-x86-64

Contents of section .gnu_debuglink:
 0000 6c696261 2e736f2e 64656275 67000000  liba.so.debug...
 0010 a1091f2f                             .../     
[zy@fedora gdb_test]$ readelf -S test|grep debug
  [28] .gnu_debuglink    PROGBITS         0000000000000000  00004768
[zy@fedora gdb_test]$ objdump -s -j .gnu_debuglink test

test：     文件格式 elf64-x86-64

Contents of section .gnu_debuglink:
 0000 74657374 2e646562 75670000 f2fa32cc  test.debug....2.

上面的objcopy --add-gnu-debuglink=liba.so.debug liba.so命令就是將指定的調試文件的名稱(liba.so.debug)及其CRC校驗值寫入到liba.so文件中。但並未告訴gdb去哪個目錄下找這個文件，gdb會去哪些路徑下找這個文件呢？在網上找到如下一段話：

So, for example, suppose you ask GDB to debug /usr/bin/ls, which has a debug link that specifies the file ls.debug, and a build ID whose value in hex is abcdef1234. If the list of the global debug directories includes /usr/lib/debug, then GDB will look for the following debug information files, in the indicated order:

- /usr/lib/debug/.build-id/ab/cdef1234.debug
- /usr/bin/ls.debug
- /usr/bin/.debug/ls.debug
- /usr/lib/debug/usr/bin/ls.debug.
Global debugging info directories default to what is set by GDB configure option --with-separate-debug-dir and augmented by the colon-separated list of directories provided via GDB configure option --additional-debug-dirs. During GDB run you can also set the global debugging info directories, and view the list GDB is currently using.

set debug-file-directory directories
Set the directories which GDB searches for separate debugging information files to directory. Multiple path components can be set concatenating them by a path separator.

show debug-file-directory
Show the directories GDB searches for separate debugging information files.

這段話以ls命令做了一個舉例。第一種build-id的方式不在本文闡述範圍之內，是另一種尋找debuginfo文件的方法，本文不再描述。對於剩餘的三個目錄，有兩個比較好理解，就是ls命令所在的目錄、ls所在目錄下的.debug目錄去尋找對應的文件。第三個比較難理解，第三個是到/usr/lib/debug/目錄下，然後根據ls目錄對應的完整路徑，到這個目錄下去尋找。就是用/usr/lib/debug目錄加上ls文件的實際路徑進行拼接後的目錄去尋找。比如一個可執行文件所在的目錄是/home/test/example,那麼gdb就回去/usr/lib/debug/home/test/下去尋找example.debug文件。再比如一個so庫所在的目錄是/home/libs/libxxx.so，那麼gdb會去/usr/lib/debug/home/libs/目錄下去尋找libxxx.so.debug文件。其它的也類似。就是將/usr/lib/debug目錄當作根目錄，然後在這個根目錄下，去可執行文件所在的目錄下去尋找對應的調試文件。因為ls命令在/usr/bin目錄下，所以gdb才會去/usr/lib/debug/usr/bin目錄下去尋找ls.debug文件。先做一個簡單的實驗，如下所示：

[zy@fedora debuginfo]$ ls
fff  test  test.debug
[zy@fedora debuginfo]$ gdb ./test
GNU gdb (Fedora Linux) 13.2-10.fc39
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./test...
Reading symbols from /home/zy/debuginfo/test.debug...

[zy@fedora debuginfo]$ ls -a
.  ..  .debug  fff  test
[zy@fedora debuginfo]$ ls .debug/
test.debug
[zy@fedora debuginfo]$ gdb ./test 
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./test...
Reading symbols from /home/zy/debuginfo/.debug/test.debug...

[zy@fedora debuginfo]$ pwd
/home/zy/debuginfo
[zy@fedora debuginfo]$ ls /usr/lib/debug/home/zy/debuginfo/test.debug 
/usr/lib/debug/home/zy/debuginfo/test.debug
[zy@fedora debuginfo]$ gdb ./test 
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./test...
Reading symbols from /usr/lib/debug//home/zy/debuginfo/test.debug...

通過上面的例子中的Reading sysbols from ......可以看到，能在對應的目錄下讀取到調試符號的信息。

對於依賴的so庫，也是一樣的道理，也會按照以上的路徑去尋找so庫所在的符號文件。如下所示：

[zy@fedora debuginfo]$ tree .
.
├── liba.so.debug
├── libs
│   ├── liba.so
│   └── liba.so.debug
├── test
└── test.debug


[zy@fedora debuginfo]$ gdb ./test
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./test...
Reading symbols from /home/zy/debuginfo/test.debug...
(gdb) b main
Breakpoint 1 at 0x40113e: file main.c, line 7.
(gdb) b liba_func
Breakpoint 2 at 0x401030
(gdb) run
Starting program: /home/zy/debuginfo/test 

This GDB supports auto-downloading debuginfo from the following URLs:
  <https://debuginfod.fedoraproject.org/>
Enable debuginfod for this session? (y or [n]) n
Debuginfod has been disabled.
To make this setting permanent, add 'set debuginfod enabled off' to .gdbinit.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Breakpoint 1, main () at main.c:7
7        int main_a = 3;
Missing separate debuginfos, use: dnf debuginfo-install glibc-2.38-10.fc39.x86_64
(gdb) n
8        int main_b = 5;
(gdb) n
9        int main_sum = 0;
(gdb) c
Continuing.
main_sum = 90.

Breakpoint 2, liba_func (a=1, b=2) at liba.c:6
6        int sum = 0;
(gdb) n
8        sum = a + b;
(gdb) n
9        printf("%d + %d = %d.\n", a, b, sum);
(gdb)

gdb也可以支持不從默認的/usr/lib/debug目錄中尋找，可以單獨指定存放debuginfo文件的根目錄。通過在gdb中的show debug-file-directory命令查看當前搜索的根目錄。通過set debug-file-directory命令可以修改搜索的根目錄。也支持設置多個根目錄，如果有多個根目錄，每個目錄之間用路徑分隔符“:“分開。如set debug-file-directory /home/test,將根目錄設置為/home/test。set debug-file-directory /home/test:/root/test，將根目錄設置為/home/test和/root/test。如下所示：

[zy@fedora debuginfo]$ gdb ./test 
GNU gdb (Fedora Linux) 13.2-10.fc39
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./test...

This GDB supports auto-downloading debuginfo from the following URLs:
  <https://debuginfod.fedoraproject.org/>
Enable debuginfod for this session? (y or [n]) n
Debuginfod has been disabled.
To make this setting permanent, add 'set debuginfod enabled off' to .gdbinit.
Missing separate debuginfo for /home/zy/debuginfo/test.
The debuginfo package for this file is probably broken.
(No debugging symbols found in ./test)
(gdb) show debug-file-directory 
The directory where separate debug symbols are searched for is "/usr/lib/debug".
(gdb) set debug-file-directory /usr/lib/debug/:/home/zy/debuginfo/debug_infos/
(gdb) b main
Function "main" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (main) pending.
(gdb) b liba_func
Breakpoint 2 at 0x401030
(gdb) run
Starting program: /home/zy/debuginfo/test 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
main_sum = 90.

Breakpoint 2, liba_func (a=1, b=2) at liba.c:6
6        int sum = 0;
Missing separate debuginfos, use: dnf debuginfo-install glibc-2.38-10.fc39.x86_64
(gdb) n
8        sum = a + b;
(gdb) n
9        printf("%d + %d = %d.\n", a, b, sum);
(gdb) n
1 + 2 = 3.
11        a = a * a;
(gdb) n
12        b = b * 2;

如上所示，liba_func可以正常斷住，可以看到調試信息。但test文件中的main函數，依然無法讀取到調試信息，斷點也並沒有停住。這是什麼原因呢？原來gdb程序在使用的時候，會主動從那幾個位置讀取被gdb的程序的調試信息，如果能讀取到，就可以看到，如果讀取不到，就認為讀取失敗。而執行set-debug-file-directory命令後，並不會再次去讀取已經認為失敗的可執行文件的調試信息，所以test的調試信息依然讀取不到。而在執行set-debug-file-directory命令後才去加載的可執行文件，就能正確讀取到調試信息。此種情況下，需要手動使用addd-symbol-file讀取那些讀取不到的可執行文件的調試信息。如下所示：

[zy@fedora debuginfo]$ gdb ./test 
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./test...

This GDB supports auto-downloading debuginfo from the following URLs:
  <https://debuginfod.fedoraproject.org/>
Enable debuginfod for this session? (y or [n]) n
Debuginfod has been disabled.
To make this setting permanent, add 'set debuginfod enabled off' to .gdbinit.
Missing separate debuginfo for /home/zy/debuginfo/test.
The debuginfo package for this file is probably broken.
(No debugging symbols found in ./test)
(gdb) set debug-file-directory /home/zy/debuginfo/debug_infos/
(gdb) add-symbol-file /home/zy/debuginfo/debug_infos/test.debug 
add symbol table from file "/home/zy/debuginfo/debug_infos/test.debug"
(y or n) y
Reading symbols from /home/zy/debuginfo/debug_infos/test.debug...
(gdb) b liba_func
Breakpoint 1 at 0x401030
(gdb) b main
Breakpoint 2 at 0x40113e: file main.c, line 7.
(gdb) run
Starting program: /home/zy/debuginfo/test 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Breakpoint 2, main () at main.c:7
7        int main_a = 3;
Missing separate debuginfos, use: dnf debuginfo-install glibc-2.38-10.fc39.x86_64
(gdb) n
8        int main_b = 5;
(gdb) n
9        int main_sum = 0;
(gdb) c
Continuing.
main_sum = 90.

Breakpoint 1, liba_func (a=1, b=2) at liba.c:6
6        int sum = 0;
(gdb) n
8        sum = a + b;
(gdb) n
9        printf("%d + %d = %d.\n", a, b, sum);
(gdb)

GDB讀取動態庫的debuginfo文件時需要注意的地方

如前所述，如果將debuginfo文件直接放到/usr/lib/debug目錄（或者通過set-debug-file-directory命令設置的根目錄）下，也是可以的，但文件目錄的組織結構必須和運行時的目錄組織結構一樣，這個地方有一個需要注意的地方，特別是對於so文件，在debug-root-directory目錄下尋找對應的debuginfo文件時，和文件實際所在的位置不一定完全一致，而要看連接器能夠找到的路徑，即ldd所顯示的路徑。gdb是會到debug-root-directory/$LDD顯示的目錄下去尋找對應的debuginfo文件。而ldd顯示出來的路徑，可能是一個絕對路徑，也可能是一個相對路徑，者取決於你的操作系統中所設置的一些so查找路徑，比如LD_LIBRARY_PATH設置為一個相對路徑還是一個絕對路徑，對於gdb來説，去debug-root-directory目錄下尋找的路徑也不一樣。gdb會拿ldd顯示出來的路徑直接和debug-root-directory拼接一下。比如我當前的LD_LIBRARY_PATH設置為.fff，那麼gdb就會去/usr/lib/debug/./fff目錄下去讀取liba.so所對應的debuginfo文件，因為ldd現實出來的liba.so的路徑是./fff/liba.so。如下所示：

[zy@fedora debuginfo]$ echo $LD_LIBRARY_PATH 
./fff
[zy@fedora debuginfo]$ tree
.
├── fff
│   └── liba.so
└── test

2 directories, 2 files
[zy@fedora debuginfo]$ ldd test 
    linux-vdso.so.1 (0x00007ffda31b6000)
    liba.so => ./fff/liba.so (0x00007f0c0a237000)
    libc.so.6 => /lib64/libc.so.6 (0x00007f0c0a03e000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f0c0a23e000)
[zy@fedora debuginfo]$ ls /usr/lib/debug/fff/liba.so.debug 
/usr/lib/debug/fff/liba.so.debug
[zy@fedora debuginfo]$ gdb ./test 
Reading symbols from ./test...

This GDB supports auto-downloading debuginfo from the following URLs:
  <https://debuginfod.fedoraproject.org/>
Enable debuginfod for this session? (y or [n]) n
Debuginfod has been disabled.
To make this setting permanent, add 'set debuginfod enabled off' to .gdbinit.
Missing separate debuginfo for /home/zy/debuginfo/test.
The debuginfo package for this file is probably broken.
(No debugging symbols found in ./test)
(gdb) b main
Function "main" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (main) pending.
(gdb) b liba_func
Breakpoint 2 at 0x401030
(gdb) run
Starting program: /home/zy/debuginfo/test 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
main_sum = 90.

Breakpoint 2, liba_func (a=1, b=2) at liba.c:6
6        int sum = 0;
Missing separate debuginfos, use: dnf debuginfo-install glibc-2.38-10.fc39.x86_64
(gdb) n
8        sum = a + b;
(gdb) n
9        printf("%d + %d = %d.\n", a, b, sum);
(gdb) n
1 + 2 = 3.
11        a = a * a;
(gdb) n
12        b = b * 2;
(gdb)

如果我將LD_LIBRARY_PATH設置為該so所在的實際絕對路徑/home/zy/debuginfo/fff/，那麼gdb就會去/usr/lib/debug/home/zy/debuginfo/fff目錄下去讀取liba.so所對應的debuginfo文件，因為ldd顯示出來的liba.so的路徑是/home/zy/debuginfo/fff/liba.so。如下所示,debuginfo文件在/usr/lib/debug/fff/liba.so.debug時，無法讀取到調試信息：

[zy@fedora debuginfo]$ export LD_LIBRARY_PATH=/home/zy/debuginfo/fff/
[zy@fedora debuginfo]$ echo $LD_LIBRARY_PATH 
/home/zy/debuginfo/fff/
[zy@fedora debuginfo]$ tree
.
├── fff
│   └── liba.so
└── test

2 directories, 2 files
[zy@fedora debuginfo]$ ldd test 
    linux-vdso.so.1 (0x00007ffc263bf000)
    liba.so => /home/zy/debuginfo/fff/liba.so (0x00007f98d6ead000)
    libc.so.6 => /lib64/libc.so.6 (0x00007f98d6cb4000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f98d6eb4000)
[zy@fedora debuginfo]$ ls /usr/lib/debug/fff/liba.so.debug 
/usr/lib/debug/fff/liba.so.debug
[zy@fedora debuginfo]$ gdb ./test 
Reading symbols from ./test...

This GDB supports auto-downloading debuginfo from the following URLs:
  <https://debuginfod.fedoraproject.org/>
Enable debuginfod for this session? (y or [n]) n
Debuginfod has been disabled.
To make this setting permanent, add 'set debuginfod enabled off' to .gdbinit.
Missing separate debuginfo for /home/zy/debuginfo/test.
The debuginfo package for this file is probably broken.
(No debugging symbols found in ./test)
(gdb) b liba_func
Breakpoint 1 at 0x401030
(gdb) run
Starting program: /home/zy/debuginfo/test 
Missing separate debuginfo for /home/zy/debuginfo/fff/liba.so.
The debuginfo package for this file is probably broken.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
main_sum = 90.

Breakpoint 1, 0x00007ffff7fbd10d in liba_func () from /home/zy/debuginfo/fff/liba.so
Missing separate debuginfos, use: dnf debuginfo-install glibc-2.38-10.fc39.x86_64
(gdb) n
Single stepping until exit from function liba_func,
which has no line number information.
1 + 2 = 3.
sum = 4.
0x000000000040118c in ?? ()
(gdb) n
Cannot find bounds of current function

而將調試文件移動到/usr/lib/debug/home/zy/debuginfo/fff/目錄後，即可讀取到正確的調試信息，如下所示：

[zy@fedora debuginfo]$ echo $LD_LIBRARY_PATH 
/home/zy/debuginfo/fff/
[zy@fedora debuginfo]$ ldd test 
    linux-vdso.so.1 (0x00007fff84fdf000)
    liba.so => /home/zy/debuginfo/fff/liba.so (0x00007f4e94e1d000)
    libc.so.6 => /lib64/libc.so.6 (0x00007f4e94c24000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f4e94e24000)
[zy@fedora debuginfo]$ ls /usr/lib/debug/home/zy/debuginfo/fff/
liba.so.debug
[zy@fedora debuginfo]$ gdb ./test 
Reading symbols from ./test...

This GDB supports auto-downloading debuginfo from the following URLs:
  <https://debuginfod.fedoraproject.org/>
Enable debuginfod for this session? (y or [n]) n
Debuginfod has been disabled.
To make this setting permanent, add 'set debuginfod enabled off' to .gdbinit.
Missing separate debuginfo for /home/zy/debuginfo/test.
The debuginfo package for this file is probably broken.
(No debugging symbols found in ./test)
(gdb) b liba_func
Breakpoint 1 at 0x401030
(gdb) run
Starting program: /home/zy/debuginfo/test 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
main_sum = 90.

Breakpoint 1, liba_func (a=1, b=2) at liba.c:6
6        int sum = 0;
Missing separate debuginfos, use: dnf debuginfo-install glibc-2.38-10.fc39.x86_64
(gdb) n
8        sum = a + b;
(gdb) n
9        printf("%d + %d = %d.\n", a, b, sum);
(gdb)

如果沒有使用環境變量，而是程序中設置了rpath目錄去讀取動態庫呢？其實是和環境變量時一樣，都是根據ldd顯示的路徑去確定的。將liba.so.debug文件放到/usr/lib/debug/fff/目錄下，通過設置rpath為$ORIGIN/fff,發現找不到調試信息，如下所示：

[zy@fedora debuginfo]$ patchelf --print-rpath test 
$ORIGIN/fff
[zy@fedora debuginfo]$ ldd test 
    linux-vdso.so.1 (0x00007ffef6ffc000)
    liba.so => /home/zy/debuginfo/./fff/liba.so (0x00007f1ea3ac9000)
    libc.so.6 => /lib64/libc.so.6 (0x00007f1ea38d0000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f1ea3ad0000)
[zy@fedora debuginfo]$ ls -l /usr/lib/debug/fff/liba.so.debug 
-rwxr-xr-x. 1 root root 5544 11月21日 22:19 /usr/lib/debug/fff/liba.so.debug
[zy@fedora debuginfo]$ gdb ./test 
This GDB supports auto-downloading debuginfo from the following URLs:
  <https://debuginfod.fedoraproject.org/>
Enable debuginfod for this session? (y or [n]) n
Debuginfod has been disabled.
To make this setting permanent, add 'set debuginfod enabled off' to .gdbinit.
Missing separate debuginfo for /home/zy/debuginfo/test.
The debuginfo package for this file is probably broken.
(No debugging symbols found in ./test)
(gdb) b liba_func
Breakpoint 1 at 0x401030
(gdb) run
Starting program: /home/zy/debuginfo/test 
Missing separate debuginfo for /home/zy/debuginfo/fff/liba.so.
The debuginfo package for this file is probably broken.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
main_sum = 90.

Breakpoint 1, 0x00007ffff7fbd10d in liba_func () from /home/zy/debuginfo/fff/liba.so
Missing separate debuginfos, use: dnf debuginfo-install glibc-2.38-10.fc39.x86_64
(gdb) n
Single stepping until exit from function liba_func,
which has no line number information.
1 + 2 = 3.
sum = 4.
0x000000000040118c in ?? ()
(gdb) n
Cannot find bounds of current function

因為ldd顯示的liba.so的目錄是/home/zy/debuginfo/./fff/liba.so，gdb在和debug-file-directory目錄拼接後的路徑是/usr/lib/debug/home/zy/debuginfo/./fff/，所以會去/usr/lib/debug/home/zy/debuginfo/./fff目錄下尋找對應的debuginfo文件，如下所示：

zy@fedora debuginfo]$ patchelf --print-rpath test 
$ORIGIN/fff
[zy@fedora debuginfo]$ ldd test 
    linux-vdso.so.1 (0x00007fff495d5000)
    liba.so => /home/zy/debuginfo/./fff/liba.so (0x00007fbf93e95000)
    libc.so.6 => /lib64/libc.so.6 (0x00007fbf93c9c000)
    /lib64/ld-linux-x86-64.so.2 (0x00007fbf93e9c000)
[zy@fedora debuginfo]$ ls /usr/lib/debug/home/zy/debuginfo/fff/
liba.so.debug
[zy@fedora debuginfo]$ gdb ./test 
Reading symbols from ./test...

This GDB supports auto-downloading debuginfo from the following URLs:
  <https://debuginfod.fedoraproject.org/>
Enable debuginfod for this session? (y or [n]) n
Debuginfod has been disabled.
To make this setting permanent, add 'set debuginfod enabled off' to .gdbinit.
Missing separate debuginfo for /home/zy/debuginfo/test.
The debuginfo package for this file is probably broken.
(No debugging symbols found in ./test)
(gdb) b liba_func
Breakpoint 1 at 0x401030
(gdb) run
Starting program: /home/zy/debuginfo/test 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
main_sum = 90.

Breakpoint 1, liba_func (a=1, b=2) at liba.c:6
6        int sum = 0;
Missing separate debuginfos, use: dnf debuginfo-install glibc-2.38-10.fc39.x86_64
(gdb) n
8        sum = a + b;
(gdb) n
9        printf("%d + %d = %d.\n", a, b, sum);

可以看到能正確的找到調試信息了。

綜上總結，gdb尋找單獨的debug文件的路徑是：

當前文件所在的目錄。
當前文件所在目錄下的.debug目錄。
debug-file-directory設置的目錄下，根據文件所在的路徑去尋找。如果是動態庫文件，則會使用ldd所顯示的目錄。可以直接使用debug-file-directory目錄+ldd顯示目錄進行拼接即可。

參考文檔

https://stackoverflow.com/questions/36070648/search-symbols-again-after-setting-debug-file-directory

https://sourceware.org/gdb/current/onlinedocs/gdb.html/Separa...

深入理解debuginfo(轉載) - 簡書

viyon 動態日志

@yuezhang_5e5e7da0beeea

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Linux (168)

調試 (18)

調試技巧 (5)

調試工具 (5)

gdb (3)

glibc (1)

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動態

gdb調試單獨的debuginfo文件 - 動態詳情

gdb調試單獨的debug文件

背景

Debug和Release區別

發佈了Release版本後，出問題時定位問題的常用做法

如何製作單獨的debuginfo文件

gdb調試單獨debuginfo文件的原理介紹

如何添加調試信息到目標文件

使用objcopy命令分離出單獨的debuginfo文件

GDB讀取動態庫的debuginfo文件時需要注意的地方

參考文檔

Add a new 評論

viyon 動態日志

@yuezhang_5e5e7da0beeea

標簽

Linux (168)

調試 (18)

調試技巧 (5)

調試工具 (5)

gdb (3)

glibc (1)

dlopen (1)

動態

gdb調試單獨的debuginfo文件 - 動態 詳情

gdb調試單獨的debug文件

背景

Debug和Release區別

發佈了Release版本後，出問題時定位問題的常用做法

如何製作單獨的debuginfo文件

gdb調試單獨debuginfo文件的原理介紹

如何添加調試信息到目標文件

使用objcopy命令分離出單獨的debuginfo文件

GDB讀取動態庫的debuginfo文件時需要注意的地方

參考文檔

Add a new 評論

gdb調試單獨的debuginfo文件 - 動態詳情