Messages in this thread | | | Date | Tue, 22 Mar 2022 19:07:34 +0700 | Subject | Re: [RFC PATCH v2 3/8] tools/nolibc: i386: Implement syscall with 6 arguments | From | Ammar Faizi <> |
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On 3/22/22 7:02 PM, Ammar Faizi wrote: > Well, I agree with your previous email. Now since we no longer use a #pragma > optimize with -fomit-frame-pointer, the function is not needed. I propose the > following macro (this is not so much different with other my_syscall macro), > expect the 6th argument can be in reg or mem. > > The "rm" constraint here gives the opportunity for the compiler to use %ebp > instead of memory if -fomit-frame-pointer is turned on. > > #define my_syscall6(num, arg1, arg2, arg3, arg4, arg5, arg6) \ > ({ \ > long _ret; \ > register long _num asm("eax") = (num); \ > register long _arg1 asm("ebx") = (long)(arg1); \ > register long _arg2 asm("ecx") = (long)(arg2); \ > register long _arg3 asm("edx") = (long)(arg3); \ > register long _arg4 asm("esi") = (long)(arg4); \ > register long _arg5 asm("edi") = (long)(arg5); \ > long _arg6 = (long)(arg6); /* Might be in memory */ \ > \ > asm volatile ( \ > "pushl %[_arg6]\n\t" \ > "pushl %%ebp\n\t" \ > "movl 4(%%esp), %%ebp\n\t" \ > "int $0x80\n\t" \ > "popl %%ebp\n\t" \ > "addl $4,%%esp\n\t" \ > : "=a"(_ret) \ > : "r"(_num), "r"(_arg1), "r"(_arg2), "r"(_arg3), \ > "r"(_arg4),"r"(_arg5), [_arg6]"rm"(_arg6) \ > : "memory", "cc" \ > ); \ > _ret; \ > }) > > What do you think? >
For the following code:
int main() { mmap(NULL, 0x1000, PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0); return 0; }
GCC generates this:
00001000 <main>: 1000: push %ebp 1001: mov $0xc0,%eax 1006: mov $0x1000,%ecx 100b: mov $0x3,%edx 1010: push %edi 1011: xor %ebp,%ebp 1013: mov $0xffffffff,%edi 1018: push %esi 1019: mov $0x22,%esi 101e: push %ebx 101f: xor %ebx,%ebx 1021: push %ebp <--- arg6 here 1022: push %ebp 1023: mov 0x4(%esp),%ebp 1027: int $0x80 1029: pop %ebp 102a: add $0x4,%esp 102d: xor %eax,%eax 102f: pop %ebx 1030: pop %esi 1031: pop %edi 1032: pop %ebp 1033: ret
-- Ammar Faizi
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