此行是造成段錯誤對我說:我可以打印使用gdb的x命令的內存,但如果我用printf,分段錯誤
30 printf("st_name:\t%s\n", &p_str_tab[p->st_name]);
我試圖追查下來,在gdb:
(gdb) p p_str_tab[p->st_name]
$11 = 0 '\000'
(gdb) p &p_str_tab[p->st_name]
$12 = 0x2aaaaaab0000 ""
(gdb) x/16s 0x2aaaaaab0000
0x2aaaaaab0000: ""
0x2aaaaaab0001: ".symtab"
0x2aaaaaab0009: ".strtab"
(gdb) call printf("st_name:\t%s\n", 0x2aaaaaab0000)
Program received signal SIGSEGV, Segmentation fault.
0x00000034f4042729 in vfprintf() from /lib64/libc.so.6
The program being debugged was signaled while in a function called from GDB.
GDB remains in the frame where the signal was received.
To change this behavior use "set unwindonsignal on".
Evaluation of the expression containing the function
我可以使用gdb的x
命令打印內存,但是如果我使用printf,則會出現分段錯誤。
爲什麼?在評論需要
UPDATE:
(gdb) x/1i $rip
0x34f4042729 <vfprintf+57>: mov 0xc0(%rdi),%eax
(gdb) info reg
rax 0x54 84
rbx 0x34f3e1bbc0 227429956544
rcx 0x0 0
rdx 0xffffffffffffffb0 -80
rsi 0x401b08 4201224
rdi 0x600908 6293768
rbp 0x7fffffffe6e0 0x7fffffffe6e0
rsp 0x7fffffffe040 0x7fffffffe040
r8 0x2aaaaaabf210 46912496202256
r9 0x34f4351780 227435419520
r10 0x1238 4664
r11 0x648 1608
r12 0x0 0
r13 0x7fffffffe9c0 140737488349632
r14 0x0 0
r15 0x0 0
rip 0x34f4042729 0x34f4042729 <vfprintf+57>
eflags 0x10202 [ IF RF ]
cs 0x33 51
ss 0x2b 43
ds 0x0 0
es 0x0 0
fs 0x0 0
gs 0x0 0
fctrl 0x37f 895
fstat 0x0 0
ftag 0xffff 65535
---Type <return> to continue, or q <return> to quit---
fiseg 0x0 0
fioff 0x0 0
foseg 0x0 0
fooff 0x0 0
fop 0x0 0
mxcsr 0x1f80 [ IM DM ZM OM UM PM ]
它有助於查看感興趣的代碼,特別是'&p_str_tab [p-> st_name]是什麼; gdb'p's應該有所幫助,但是我看不到有效性,肯定會漏掉一些東西;關於x,是否有可能gdb可以安全地讀取比程序本身可以訪問更多的內存?我應該檢查 – ShinTakezou
@ShinTakezou,'&p_str_tab [p-> st_name]'指向'0x2aaaaaab0000'處的符號表,如上所示。 –
你可以在SEGV之後做'x/1i $ rip'和'info reg'嗎? – ninjalj