int 80, i think, is hardly used nowadays: http://wiki.osdev.org/System_Calls http://articles.manugarg.com/systemcallinlinux2_6.html http://semipublic.comp-arch.net/wiki/SYSENTER/SYSEXIT_vs._SYSCALL/SYSRET and even for SYSENTER instruction, it will not be compiled into your program, but exists inside some external libraries, unless u compile it as static. On Sun, Jul 15, 2012 at 10:28 AM, 王哲 <wangzhe5004@gmail.com> wrote:
Hi all:
i write two simple program to invoke syscall getpid.
the first program (getpid1.c) is as followed: #include <stdio.h> #include <unistd.h>
int main(void) { unsigned long value = 0; __asm__("int $0x80":"=a"(value):"0"(20)); return 0; }
and use objdump -d a.out disassembling it : ... 80483c2: b8 14 00 00 00 mov $0x14,%eax 80483c7: 89 c3 mov %eax,%ebx 80483c9: 89 d8 mov %ebx,%eax 80483cb: cd 80 int $0x80 ...
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> ... 080483e4 <main>: 80483e4: 55 push %ebp 80483e5: 89 e5 mov %esp,%ebp 80483e7: 83 e4 f0 and $0xfffffff0,%esp 80483ea: 83 ec 10 sub $0x10,%esp 80483ed: c7 44 24 0c 00 00 00 movl $0x0,0xc(%esp) 80483f4: 00 80483f5: e8 06 ff ff ff call 8048300 <getpid@plt> 80483fa: 89 44 24 0c mov %eax,0xc(%esp) 80483fe: b8 00 00 00 00 mov $0x0,%eax ...
question: why i can't find the "movl $0x14,%eax" "int 0x80" in the second program after disassembling?
any advice will be help! thanks in advance! wanny
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