c - 使用 gdb 查找 C 中未知函数的作用

Question

我有一个函数 m(int i, char c)，它接受并返回“-abc...xyz”之间的一个字符，并且还接受一个整数 i。

基本上我无法查看该函数的源代码，但可以调用它并获取返回值。使用 gdb/C，解读该函数实际功能的最佳方法是什么？我尝试过使用连续字符和整数输入来寻找模式，但还没有找到任何结果。

如果有帮助，这里是测试返回值的一些结果，前两位是参数，最后一位是返回值:

0 a    i
0 b    l
0 c    t
0 d    x
0 e    f
0 f    v

1 a    q
1 b    i
1 c    y
1 d    e

2 a    a
2 b    y
2 c    f
2 d    n

反汇编提供以下内容:

0x00014354 <m+0>:    save  %sp, -144, %sp
0x00014358 <m+4>:    st  %i0, [ %fp + 0x44 ]
0x0001435c <m+8>:    mov  %i1, %g1
0x00014360 <m+12>:   stb  %g1, [ %fp + 0x48 ]
0x00014364 <m+16>:   st  %sp, [ %fp + -40 ]
0x00014368 <m+20>:   mov  0x1b, %g1
0x0001436c <m+24>:   stb  %g1, [ %fp + -17 ]
0x00014370 <m+28>:   clr  [ %fp + -24 ]
0x00014374 <m+32>:   ldub  [ %fp + -17 ], %g1
0x00014378 <m+36>:   sll  %g1, 0x18, %g1
0x0001437c <m+40>:   sra  %g1, 0x18, %g1
0x00014380 <m+44>:   add  %g1, 7, %g1
0x00014384 <m+48>:   srl  %g1, 3, %g1
0x00014388 <m+52>:   sll  %g1, 3, %g1
0x0001438c <m+56>:   sub  %sp, %g1, %sp
0x00014390 <m+60>:   add  %sp, 0x5c, %g1
0x00014394 <m+64>:   add  %g1, 7, %g1
0x00014398 <m+68>:   srl  %g1, 3, %g1
0x0001439c <m+72>:   sll  %g1, 3, %g1
0x000143a0 <m+76>:   st  %g1, [ %fp + -44 ]
0x000143a4 <m+80>:   mov  0x2d, %g1
0x000143a8 <m+84>:   ld  [ %fp + -44 ], %o4
0x000143ac <m+88>:   stb  %g1, [ %o4 ]
0x000143b0 <m+92>:   mov  1, %g1
0x000143b4 <m+96>:   st  %g1, [ %fp + -28 ]
0x000143b8 <m+100>:  ldub  [ %fp + -17 ], %g1
0x000143bc <m+104>:  sll  %g1, 0x18, %g1
0x000143c0 <m+108>:  sra  %g1, 0x18, %o5
0x000143c4 <m+112>:  ld  [ %fp + -28 ], %g1
0x000143c8 <m+116>:  cmp  %o5, %g1
0x000143cc <m+120>:  ble  0x14400 <m+172>
0x000143d0 <m+124>:  nop 
0x000143d4 <m+128>:  ld  [ %fp + -28 ], %g1
0x000143d8 <m+132>:  ld  [ %fp + -44 ], %o4
0x000143dc <m+136>:  add  %o4, %g1, %o5
0x000143e0 <m+140>:  ld  [ %fp + -28 ], %g1
0x000143e4 <m+144>:  add  %g1, 0x60, %g1
0x000143e8 <m+148>:  stb  %g1, [ %o5 ]
0x000143ec <m+152>:  ld  [ %fp + -28 ], %g1
0x000143f0 <m+156>:  inc  %g1
0x000143f4 <m+160>:  st  %g1, [ %fp + -28 ]
0x000143f8 <m+164>:  b  0x143b8 <m+100>
0x000143fc <m+168>:  nop 
0x00014400 <m+172>:  ldub  [ %fp + -17 ], %g1
0x00014404 <m+176>:  sll  %g1, 0x18, %g1
0x00014408 <m+180>:  sra  %g1, 0x18, %o5
0x0001440c <m+184>:  ld  [ %fp + 0x44 ], %g1
0x00014410 <m+188>:  mov  %g1, %o0
0x00014414 <m+192>:  mov  %o5, %o1
0x00014418 <m+196>:  call  0x2727c <.rem@plt>
0x0001441c <m+200>:  nop 
0x00014420 <m+204>:  mov  %o0, %g1
0x00014424 <m+208>:  st  %g1, [ %fp + 0x44 ]
0x00014428 <m+212>:  ldub  [ %fp + 0x48 ], %g1
0x0001442c <m+216>:  sll  %g1, 0x18, %g1
0x00014430 <m+220>:  sra  %g1, 0x18, %g1
0x00014434 <m+224>:  cmp  %g1, 0x2d
0x00014438 <m+228>:  be  0x1449c <m+328>
0x0001443c <m+232>:  nop 
0x00014440 <m+236>:  ldub  [ %fp + 0x48 ], %g1
0x00014444 <m+240>:  sll  %g1, 0x18, %g1
0x00014448 <m+244>:  sra  %g1, 0x18, %g1
0x0001444c <m+248>:  cmp  %g1, 0x60
0x00014450 <m+252>:  bg  0x14464 <m+272>
0x00014454 <m+256>:  nop 
0x00014458 <m+260>:  clr  [ %fp + -24 ]
0x0001445c <m+264>:  b  0x1449c <m+328>
0x00014460 <m+268>:  nop 
0x00014464 <m+272>:  ldub  [ %fp + 0x48 ], %g1
0x00014468 <m+276>:  sll  %g1, 0x18, %g1
0x0001446c <m+280>:  sra  %g1, 0x18, %g1
0x00014470 <m+284>:  cmp  %g1, 0x7a
0x00014474 <m+288>:  ble  0x14488 <m+308>
0x00014478 <m+292>:  nop 
0x0001447c <m+296>:  clr  [ %fp + -24 ]
0x00014480 <m+300>:  b  0x1449c <m+328>
0x00014484 <m+304>:  nop 
0x00014488 <m+308>:  ldub  [ %fp + 0x48 ], %g1
0x0001448c <m+312>:  sll  %g1, 0x18, %g1
0x00014490 <m+316>:  sra  %g1, 0x18, %g1
0x00014494 <m+320>:  add  %g1, -96, %g1
0x00014498 <m+324>:  st  %g1, [ %fp + -24 ]
0x0001449c <m+328>:  clr  [ %fp + -28 ]
0x000144a0 <m+332>:  ldub  [ %fp + -17 ], %g1
0x000144a4 <m+336>:  sll  %g1, 0x18, %g1
0x000144a8 <m+340>:  sra  %g1, 0x18, %o5
0x000144ac <m+344>:  ld  [ %fp + -28 ], %g1
0x000144b0 <m+348>:  cmp  %o5, %g1
0x000144b4 <m+352>:  ble  0x14568 <m+532>
0x000144b8 <m+356>:  nop 
0x000144bc <m+360>:  ld  [ %fp + 0x44 ], %g1
0x000144c0 <m+364>:  sll  %g1, 3, %l0
0x000144c4 <m+368>:  ld  [ %fp + -28 ], %o0
0x000144c8 <m+372>:  ld  [ %fp + -28 ], %o1
0x000144cc <m+376>:  call  0x272ac <.umul@plt>
0x000144d0 <m+380>:  nop 
0x000144d4 <m+384>:  mov  %o0, %g1
0x000144d8 <m+388>:  add  %l0, %g1, %g1
0x000144dc <m+392>:  add  %g1, 8, %o5
0x000144e0 <m+396>:  ldub  [ %fp + -17 ], %g1
0x000144e4 <m+400>:  sll  %g1, 0x18, %g1
0x000144e8 <m+404>:  sra  %g1, 0x18, %g1
0x000144ec <m+408>:  mov  %o5, %o0
0x000144f0 <m+412>:  mov  %g1, %o1
0x000144f4 <m+416>:  call  0x2727c <.rem@plt>
0x000144f8 <m+420>:  nop 
0x000144fc <m+424>:  mov  %o0, %g1
0x00014500 <m+428>:  st  %g1, [ %fp + -32 ]
0x00014504 <m+432>:  ld  [ %fp + -32 ], %g1
0x00014508 <m+436>:  ld  [ %fp + -44 ], %o5
0x0001450c <m+440>:  add  %o5, %g1, %g1
0x00014510 <m+444>:  ldub  [ %g1 ], %g1
0x00014514 <m+448>:  sll  %g1, 0x18, %g1
0x00014518 <m+452>:  sra  %g1, 0x18, %g1
0x0001451c <m+456>:  st  %g1, [ %fp + -36 ]
0x00014520 <m+460>:  ld  [ %fp + -32 ], %g1
0x00014524 <m+464>:  ld  [ %fp + -44 ], %o4
0x00014528 <m+468>:  add  %o4, %g1, %o5
0x0001452c <m+472>:  ld  [ %fp + -28 ], %g1
0x00014530 <m+476>:  ld  [ %fp + -44 ], %o4
0x00014534 <m+480>:  add  %o4, %g1, %g1
0x00014538 <m+484>:  ldub  [ %g1 ], %g1
0x0001453c <m+488>:  stb  %g1, [ %o5 ]
0x00014540 <m+492>:  ld  [ %fp + -28 ], %g1
0x00014544 <m+496>:  ld  [ %fp + -44 ], %o4
0x00014548 <m+500>:  add  %o4, %g1, %o5
0x0001454c <m+504>:  ld  [ %fp + -36 ], %g1
0x00014550 <m+508>:  stb  %g1, [ %o5 ]
0x00014554 <m+512>:  ld  [ %fp + -28 ], %g1
0x00014558 <m+516>:  inc  %g1
0x0001455c <m+520>:  st  %g1, [ %fp + -28 ]
0x00014560 <m+524>:  b  0x144a0 <m+332>
0x00014564 <m+528>:  nop 
0x00014568 <m+532>:  ld  [ %fp + -24 ], %g1
0x0001456c <m+536>:  ld  [ %fp + -44 ], %o5
0x00014570 <m+540>:  add  %o5, %g1, %g1
0x00014574 <m+544>:  ldub  [ %g1 ], %g1
0x00014578 <m+548>:  sll  %g1, 0x18, %g1
0x0001457c <m+552>:  sra  %g1, 0x18, %g1
0x00014580 <m+556>:  ld  [ %fp + -40 ], %sp
0x00014584 <m+560>:  mov  %g1, %i0
0x00014588 <m+564>:  ret 
0x0001458c <m+568>:  restore

Answer 1

看反汇编:

gdb ./prog
b FUNCTION_NAME_HERE
r
disassemble

编辑:

反汇编看起来像 SPARC。您可能需要首先检查 SPARC 架构的堆栈布局:

http://www.sics.se/~psm/sparcstack.html

%fp 听起来像帧指针。使用 %fp 的加载指令并不多。我的猜测是

0x000143d4 <m+128>:  ld  [ %fp + -28 ], %g1
0x000143d8 <m+132>:  ld  [ %fp + -44 ], %o4

是函数的参数。