Hi Mulyadi and WangZhe, Nice to write to you again....:-). On Sun, Jul 15, 2012 at 1:49 PM, Mulyadi Santosa <mulyadi.santosa@gmail.com>wrote:
Hi...
On Sun, Jul 15, 2012 at 9:28 AM, 王哲 <wangzhe5004@gmail.com> wrote:
and the second program:
#include <stdio.h> #include <unistd.h>
int main(void) { unsigned long value = 0; value = getpid(); return 0; }
and disassembling it:( objdump -d a.out) ... 08048300 <getpid@plt>: 8048300: ff 25 00 a0 04 08 jmp *0x804a000 8048306: 68 00 00 00 00 push $0x0 804830b: e9 e0 ff ff ff jmp 80482f0 <_init+0x3c>
Looks like jumping into vsyscall page to me...
after I start the process, and doing a gdb -p <pid>: (gdb) disassemble main Dump of assembler code for function main: 0x0000000000400564 <+0>: push %rbp 0x0000000000400565 <+1>: mov %rsp,%rbp 0x0000000000400568 <+4>: sub $0x10,%rsp 0x000000000040056c <+8>: movq $0x0,-0x8(%rbp) 0x0000000000400574 <+16>: mov $0x0,%eax 0x0000000000400579 <+21>: callq 0x400460 <getpid@plt> 0x000000000040057e <+26>: cltq 0x0000000000400580 <+28>: mov %rax,-0x8(%rbp) 0x0000000000400584 <+32>: movabs $0x9184e72a000,%rdi 0x000000000040058e <+42>: mov $0x0,%eax 0x0000000000400593 <+47>: callq 0x400470 <sleep@plt> 0x0000000000400598 <+52>: mov $0x0,%eax 0x000000000040059d <+57>: leaveq 0x000000000040059e <+58>: retq End of assembler dump. (gdb) disassemble getpid Dump of assembler code for function getpid: 0x00007f19ae558530 <+0>: mov %fs:0x2d4,%edx 0x00007f19ae558538 <+8>: cmp $0x0,%edx 0x00007f19ae55853b <+11>: jle 0x7f19ae558540 <getpid+16> 0x00007f19ae55853d <+13>: mov %edx,%eax 0x00007f19ae55853f <+15>: retq 0x00007f19ae558540 <+16>: jne 0x7f19ae558554 <getpid+36> 0x00007f19ae558542 <+18>: mov %fs:0x2d0,%eax 0x00007f19ae55854a <+26>: test %eax,%eax 0x00007f19ae55854c <+28>: nopl 0x0(%rax) 0x00007f19ae558550 <+32>: je 0x7f19ae558554 <getpid+36> 0x00007f19ae558552 <+34>: repz retq 0x00007f19ae558554 <+36>: mov $0x27,%eax 0x00007f19ae558559 <+41>: syscall 0x00007f19ae55855b <+43>: test %edx,%edx 0x7f19ae55855d <getpid+45>: jne 0x7f19ae558552 <getpid+34> 0x7f19ae55855f <getpid+47>: mov %eax,%fs:0x2d0 0x7f19ae558567 <getpid+55>: retq And to check the address space: (gdb) info sharedlibrary
From To Syms Read Shared Object Library 0x00007f19ae4cb8c0 0x00007f19ae5dec60 Yes (*) /lib/libc.so.6 0x00007f19ae830af0 0x00007f19ae849704 Yes (*) /lib64/ld-linux-x86-64.so.2 (*): Shared library is missing debugging information.
and if u want: cat /proc/2282/maps 7f19ae82a000-7f19ae82b000 rw-p 0017d000 08:05 9922 /lib/libc-2.11.1.so 7f19ae830000-7f19ae850000 r-xp 00000000 08:05 8824 /lib/ld-2.11.1.so 7ffff2031000-7ffff2052000 rw-p 00000000 00:00 0 [stack] 7ffff21af000-7ffff21b0000 r-xp 00000000 00:00 0 [vdso] ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall] noticed also that static analysis tools like "objdump -d" is generally avoided, if u want to understand dynamic addresses. From above, we can conclude that the "sysenter" (this is intel syntax, or "syscall", in AMD syntax as used by gdb disassembly above) is used for the transition to the kernel - as embedded inside the libc.so.6.
-- regards,
Mulyadi Santosa Freelance Linux trainer and consultant
blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com
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-- Regards, Peter Teoh