Non-sequiturTyler wrote:Does linux make use of SYSCALL under x86 as well as INT 0x80?
According to the intel manuals, there is a special SYSCALL instruction, are you saying they don't use it for compatability with Unix?SpooK wrote:Non-sequiturTyler wrote:Does linux make use of SYSCALL under x86 as well as INT 0x80?
IIRC, The Linux "SYSCALL" on the x86 is based on UNIX, that being software generated INT 0x80.
Linux uses Int 0x80. Simple.Tyler wrote:According to the intel manuals, there is a special SYSCALL instruction, are you saying they don't use it for compatability with Unix?
Actually, recent linux versions have a "vsyscall page" mapped into a high memory address. It contains instructions for what Linux has determined (at startup) to be the best way to perform a system call, which applications can call as an alternative to int 0x80.Alboin wrote:Linux uses Int 0x80. Simple.Tyler wrote:According to the intel manuals, there is a special SYSCALL instruction, are you saying they don't use it for compatability with Unix?
Code: Select all
#include <stdio.h>
void *vdso = (void*) 0xffffe000;
int main() {
FILE* f = fopen("vdso.elf", "wb+");
fwrite(vdso, 0x1000, 1, f);
fclose(f);
return 0;
}Code: Select all
$ objdump -d vdso.elf
vdso.elf: file format elf32-i386
Disassembly of section .text.vsyscall:
ffffe400 <__kernel_vsyscall>:
ffffe400: 55 push ebp
ffffe401: 89 cd mov ebp,ecx
ffffe403: 0f 05 syscall
ffffe405: b9 2b 00 00 00 mov ecx,0x2b
ffffe40a: 8e d1 movl ss,ecx
ffffe40c: 89 e9 mov ecx,ebp
ffffe40e: 5d pop ebp
ffffe40f: c3 ret
Disassembly of section .text.sigreturn:
ffffe500 <__kernel_sigreturn>:
ffffe500: 58 pop eax
ffffe501: b8 77 00 00 00 mov eax,0x77
ffffe506: 0f 05 syscall
Disassembly of section .text.rtsigreturn:
ffffe600 <__kernel_rt_sigreturn>:
ffffe600: b8 ad 00 00 00 mov eax,0xad
ffffe605: 0f 05 syscall