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https://github.com/beyondx/Notes.git
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251 lines
9.8 KiB
Plaintext
251 lines
9.8 KiB
Plaintext
Content-Type: text/x-zim-wiki
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Wiki-Format: zim 0.4
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Creation-Date: 2012-12-25T10:31:03+08:00
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====== gdb frame ======
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Created Tuesday 25 December 2012
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char **friends = {"Tom", "John", "Pi", \0};
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等价于 char *friends[ ] = {"Tom", "John", "Pi", \0};
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等价于 char *friends[4] = {"Tom", "John", "Pi", \0};
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[geekard@geekard rel]$ gdb rel2
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GNU gdb (GDB) 7.5.1
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**(gdb) b greeting**
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Breakpoint 1 at 0x8048432: file rel2.c, line 8.
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**(gdb) r**
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Starting program: /home/geekard/Code/elf/rel/rel2
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warning: Could not load shared library symbols for linux-gate.so.1.
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Do you need "set solib-search-path" or "set sysroot"?
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3
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Breakpoint 1, greeting (name=0x80485c9 "geekard", age=23, friends=0xbffff944) at rel2.c:8
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8 printf("Hello, %s:\n", name);
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**(gdb) disassemble**
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Dump of assembler code for function greeting:
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0x0804842c <+0>: push %ebp
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0x0804842d <+1>: mov %esp,%ebp
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0x0804842f <+3>: sub $0x18,%esp
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上面这三条指令称为prologue，由gcc自动添加。break fuction会在执行完function的prologue后停止，这样
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=> 0x08048432 <+6>: mov 0x8(%ebp),%eax
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0x08048435 <+9>: mov %eax,0x4(%esp)
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0x08048439 <+13>: movl $0x8048590,(%esp)
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0x08048440 <+20>: call 0x80482f0 <printf@plt>
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**(gdb) si //多次执行si，直到输出如下字符串**
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0x080482f0 in printf@plt ()
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**(gdb) bt**
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#0 0x080482f0 in printf@plt ()
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#1 0x08048445 in greeting (name=0x80485c9 "geekard", age=23, friends=0xbffff944) at rel2.c:8
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#2 0x080484fd in main () at [[rel2.c:28]]
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**(gdb) info frame 2**
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Stack frame at 0xbffff970:
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eip = 0x80484fd in main (rel2.c:28); saved eip 0xb7e28605
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caller of frame at 0xbffff930
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source language c.
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Arglist at 0xbffff968, args:
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Locals at 0xbffff968, Previous frame's sp is 0xbffff970
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Saved registers:
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ebp at 0xbffff968, eip at 0xbffff96c
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**(gdb) info frame 1**
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Stack frame at 0xbffff930:
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eip = 0x8048445 in greeting (rel2.c:8); saved eip 0x80484fd
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called by frame at 0xbffff970, caller of frame at 0xbffff910
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source language c.
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Arglist at 0xbffff928, args: name=0x80485c9 "geekard", age=23, friends=0xbffff944
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Locals at 0xbffff928, Previous frame's sp is 0xbffff930
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Saved registers:
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ebp at 0xbffff928, eip at 0xbffff92c
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**(gdb) info frame 0**
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Stack frame at 0xbffff910:
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eip = 0x80482f0 in printf@plt; saved eip 0x8048445
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called by frame at 0xbffff930
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Arglist at 0xbffff908, args:
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Locals at 0xbffff908, Previous frame's sp is 0xbffff910
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Saved registers: //没有保存ebp, esi, edi, ebx寄存器的值。
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eip at 0xbffff90c
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**(gdb) disassemble main**
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Dump of assembler code for function main:
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0x0804848a <+0>: push %ebp
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0x0804848b <+1>: mov %esp,%ebp
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0x0804848d <+3>: and $0xfffffff0,%esp
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0x08048490 <+6>: sub $0x30,%esp
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0x08048493 <+9>: mov 0x8049804,%eax
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0x08048498 <+14>: mov %eax,0x2c(%esp)
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0x0804849c <+18>: movl $0x80485c9,0x28(%esp)
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0x080484a4 <+26>: movl $0x17,0x24(%esp)
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0x080484ac <+34>: movl $0x80485d1,0x14(%esp)
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0x080484b4 <+42>: movl $0x80485d5,0x18(%esp)
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0x080484bc <+50>: movl $0x80485da,0x1c(%esp)
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0x080484c4 <+58>: movl $0x0,0x20(%esp)
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0x080484cc <+66>: mov 0x8049808,%eax
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0x080484d1 <+71>: mov %eax,0x4(%esp)
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0x080484d5 <+75>: movl $0x80485dd,(%esp)
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0x080484dc <+82>: call 0x80482f0 <printf@plt>
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0x080484e1 <+87>: lea 0x14(%esp),%eax
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0x080484e5 <+91>: mov %eax,0x8(%esp)
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0x080484e9 <+95>: mov 0x24(%esp),%eax
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0x080484ed <+99>: mov %eax,0x4(%esp)
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0x080484f1 <+103>: mov 0x28(%esp),%eax
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0x080484f5 <+107>: mov %eax,(%esp)
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0x080484f8 <+110>: call __0x804842c__ <greeting>
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__0x080484fd__ <+115>: leave
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0x080484fe <+116>: ret
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End of assembler dump.
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**(gdb) disassemble greeting**
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Dump of assembler code for function greeting:
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0x0804842c <+0>: push %ebp
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0x0804842d <+1>: mov %esp,%ebp
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0x0804842f <+3>: sub $0x18,%esp
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0x08048432 <+6>: mov 0x8(%ebp),%eax
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0x08048435 <+9>: mov %eax,0x4(%esp)
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0x08048439 <+13>: movl $0x8048590,(%esp)
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0x08048440 <+20>: call __0x80482f0__ <printf@plt>
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__0x08048445__ <+25>: mov 0xc(%ebp),%eax
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0x08048448 <+28>: mov %eax,0x4(%esp)
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0x0804844c <+32>: movl $0x804859c,(%esp)
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0x08048453 <+39>: call 0x80482f0 <printf@plt>
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0x08048458 <+44>: movl $0x80485af,(%esp)
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0x0804845f <+51>: call 0x8048300 <puts@plt>
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0x08048464 <+56>: jmp 0x804847f <greeting+83>
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0x08048466 <+58>: mov 0x10(%ebp),%eax
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0x08048469 <+61>: mov (%eax),%eax
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0x0804846b <+63>: mov %eax,0x4(%esp)
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0x0804846f <+67>: movl $0x80485c3,(%esp)
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0x08048476 <+74>: call 0x80482f0 <printf@plt>
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0x0804847b <+79>: addl $0x4,0x10(%ebp)
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0x0804847f <+83>: mov 0x10(%ebp),%eax
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0x08048482 <+86>: mov (%eax),%eax
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0x08048484 <+88>: test %eax,%eax
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0x08048486 <+90>: jne 0x8048466 <greeting+58>
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0x08048488 <+92>: leave
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0x08048489 <+93>: ret
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End of assembler dump.
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**(gdb) x /8wx 0x80482f0**
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0x80482f0 <printf@plt>: 0x97ec25ff 0x00680804 0xe9000000 0xffffffe0
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0x8048300 <puts@plt>: 0x97f025ff 0x08680804 0xe9000000 0xffffffd0
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**(gdb) x /8wi 0x80482f0**
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__0x80482f0__ <printf@plt>: jmp *__0x80497ec__
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0x80482f6 <printf@plt+6>: push $0x0
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0x80482fb <printf@plt+11>: jmp 0x80482e0
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0x8048300 <puts@plt>: jmp *0x80497f0
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0x8048306 <puts@plt+6>: push $0x8
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0x804830b <puts@plt+11>: jmp 0x80482e0
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0x8048310 <__gmon_start__@plt>: jmp *0x80497f4
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0x8048316 <__gmon_start__@plt+6>: push $0x10
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**(gdb) x /wx 0x80497ec**
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0x80497ec <printf@got.plt>: 0xb7e5bed0
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**(gdb) si**
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0xb7e5bed0 in printf () from [[/usr/lib/libc.so.6]]
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**(gdb) disassemble *0x80497ec**
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Dump of assembler code for function __printf__:
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=> __0xb7e5bed0__ <+0>: push %ebx
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0xb7e5bed1 <+1>: sub $0x18,%esp
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0xb7e5bed4 <+4>: call 0xb7f376d3 <__x86.get_pc_thunk.bx>
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0xb7e5bed9 <+9>: add $0x159127,%ebx
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0xb7e5bedf <+15>: lea 0x24(%esp),%eax
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0xb7e5bee3 <+19>: mov %eax,0x8(%esp)
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0xb7e5bee7 <+23>: mov 0x20(%esp),%eax
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0xb7e5beeb <+27>: mov %eax,0x4(%esp)
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0xb7e5beef <+31>: mov -0x68(%ebx),%eax
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0xb7e5bef5 <+37>: mov (%eax),%eax
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0xb7e5bef7 <+39>: mov %eax,(%esp)
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0xb7e5befa <+42>: call 0xb7e520f0 <vfprintf>
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0xb7e5beff <+47>: add $0x18,%esp
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0xb7e5bf02 <+50>: pop %ebx
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0xb7e5bf03 <+51>: ret
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End of assembler dump.
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**(gdb) bt**
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#0 0xb7e5bed0 in printf () from /usr/lib/libc.so.6
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#1 0x08048445 in greeting (name=0x80485c9 "geekard", age=23, friends=0xbffff944) at rel2.c:8
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#2 0x080484fd in main () at rel2.c:28
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**(gdb) info f 0**
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Stack frame at 0xbffff910:
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eip = 0xb7e5bed0 in printf; saved eip 0x8048445
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called by frame at 0xbffff930
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Arglist at 0xbffff908, args:
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Locals at 0xbffff908, Previous frame's sp is 0xbffff910
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Saved registers:
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eip at 0xbffff90c
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没有保存ebp, esi, edi, ebx等寄存器的值，所以它们的值与frame 1中的相等。在编译时如果指定-fomit-frame-pointer选项，则
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编译器为函数调用生成栈帧时不会圧入ebp寄存器的值，而且对arguments和auto variables的引用是通过esp进行的。这样可以将
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ebp寄存器节省出来，用作其它用途。但缺点是无法对函数调用进行frame backtrace（如果目标文件中有.eh_frame section则gdb可以
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从中提取出frame backtrace信息）。
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**(gdb) info registers**
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eax 0x80485c9 134514121
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ecx 0x0 0
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edx 0x0 0
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ebx 0xb7fb5000 -1208266752 //继续保存的是frame 1中的值
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esp 0xbffff90c 0xbffff90c
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ebp 0xbffff928 0xbffff928 //继续保存的是frame 1中的值
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esi 0x0 0
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edi 0x0 0
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eip 0xb7e5bed0 0xb7e5bed0 <printf>
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eflags 0x200282 [ SF IF ID ]
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cs 0x73 115
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ss 0x7b 123
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ds 0x7b 123
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es 0x7b 123
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fs 0x0 0
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gs 0x33 51
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**(gdb) f 1 //切换frame到#1, 这样可以查看greeting函数的参数和自动变量值。**
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#1 0x08048445 in greeting (name=0x80485c9 "geekard", age=23, friends=0xbffff944) at rel2.c:8
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8 printf("Hello, %s:\n", name);
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**(gdb) info registers** //打印frame 1的寄存器
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eax 0x80485c9 134514121
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ecx 0x0 0
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edx 0x0 0
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ebx **0xb7fb5000** -1208266752
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esp 0xbffff910 0xbffff910
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ebp **0xbffff928** 0xbffff928
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esi 0x0 0
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edi 0x0 0
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eip 0x8048445 0x8048445 <greeting+25>
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eflags 0x200282 [ SF IF ID ]
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cs 0x73 115
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ss 0x7b 123
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ds 0x7b 123
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es 0x7b 123
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fs 0x0 0
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gs 0x33 51
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(gdb)
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(gdb)
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**(gdb) info args**
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name = 0x80485c9 "geekard"
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age = 23
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friends = 0xbffff944
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**(gdb) ptype friends**
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type = char **
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**(gdb) p friends**
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$1 = (char **) 0xbffff944
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**(gdb) p *friends**
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$6 = 0x80485d1 "Tom"
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**(gdb) p friends+1**
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$2 = (char **) 0xbffff948
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**(gdb) x /4wx friends**
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0xbffff944: 0x080485d1 0x080485d5 0x080485da 0x00000000
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**(gdb) p *friends@4**
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$4 = {0x80485d1 "Tom", 0x80485d5 "John", 0x80485da "Pi", 0x0}
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**(gdb) p &friends**
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$5 = (char ***) 0xbffff938
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(**gdb) x /4wx friends+1**
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0xbffff948: 0x080485d5 0x080485da 0x00000000 0x00000017
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**(gdb) x /4wx &friends**
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0xbffff938: 0xbffff944 0x08048552 0x00000001 0x080485d1
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**(gdb) p friends@4**
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$3 = {0xbffff944, 0x8048552 <__libc_csu_init+82>, 0x1, 0x80485d1}
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**(gdb) x /wx friends**
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0xbffff944: 0x080485d1
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**(gdb) x /wx friends+1**
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0xbffff948: 0x080485d5
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**(gdb) x /wx &friends**
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0xbffff938: 0xbffff944
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**(gdb) x /wx *friends**
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0x80485d1: 0x006d6f54
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