GDB

https://sourceware.org/gdb/onlinedocs/gdb/Define.html

打印整个链表:

define plist
  set var $n = $arg0
  while $n
    p *$n
    set var $n = $n->next
  end
end

(gdb) dump binary memory ./file <from> <to>

$> cat test.c

extern void foo();
int main(int argc, char *argv[]) {
    foo();
}

$> cat foo.c

void foo() {
    sleep(100000);
    printf("hello\n");
}

$> gcc -shared -O0 -g foo.c -o libfoo.so
$> gcc test.c -L. -lfoo
$> LD_LIBRARY_PATH=. ./a.out
...
$> mv libfoo.so ~/download
$> sudo gdb a.out
(gdb) attach 10511
Attaching to program: /home/sunway/a.out, process 10511
warning: Could not load shared library symbols for ./libfoo.so.
Do you need "set solib-search-path" or "set sysroot"?
Reading symbols from /usr/lib/libc.so.6...(no debugging symbols found)...done.
Reading symbols from /lib64/ld-linux-x86-64.so.2...(no debugging symbols found)...done.
0x00007f7dfb79f1b1 in nanosleep () from /usr/lib/libc.so.6

(gdb) info sharedlibrary
From                To                  Syms Read   Shared Object Library
                                        No          ./libfoo.so
0x00007f7dfb6fb790  0x00007f7dfb83dc0c  Yes (*)     /usr/lib/libc.so.6
0x00007f7dfbc95db0  0x00007f7dfbcb23e0  Yes (*)     /lib64/ld-linux-x86-64.so.2
(*): Shared library is missing debugging information.

$> cat /proc/10511/maps|grep libfoo
7f7dfba93000-7f7dfba94000 r-xp 00000000 08:03 17043246                   /home/sunway/download/libfoo.so
...

$> readelf -a ~/download/libfoo.so|grep .text
  [11] .text             PROGBITS         0000000000000560  00000560
                                          ~~~~~~~~~~~~~~~~

(gdb) add-symbol-file ~/download/libfoo.so 0x7f7dfba93000+0x560
add symbol table from file "/home/sunway/download/libfoo.so" at
        .text_addr = 0x7f7dfba93560
(y or n) y
Reading symbols from /home/sunway/download/libfoo.so...done.

(gdb) bt
#0  0x00007f7dfb79f1b1 in nanosleep () from /usr/lib/libc.so.6
#1  0x00007f7dfb79f0ea in sleep () from /usr/lib/libc.so.6
#2  0x00007f7dfba9364d in foo () at foo.c:2
#3  0x00005629c2e4a723 in main ()

# 使用 call 来调用函数
(gdb) call print_rtl_single(stdout, insn)

# call 的返回值
(gdb) call PATTERN(insn)
$10 = (rtx &) @0x7ffff7676920: 0x7ffff778a288
(gdb) p *$10
...

# 可以使用 $ 引用最近的返回值, 即 $10
# 使用 set $xxx 可以保存这个返回值到另一个名字
(gdb) set $pat=$
(gdb) p *$pat

break 后可以用 commands 指定每次在断点处自动执行的命令, 例如打印变量的值

(gdb) break xxx
# 假设前面的 break 是 2
(gdb) commands 2
Type commands for breakpoint(s) 1, one per line.
End with a line saying just "end".
>p /c xxx
>     
>end

# 再次指定一个空的 commands, 相当于去除 break 2 的 commands
(gdb) commands 2
Type commands for breakpoint(s) 1, one per line.
End with a line saying just "end".
>     
>end