Messages in this thread | | | Date | Tue, 22 Mar 2022 19:02:53 +0700 | From | Ammar Faizi <> | Subject | Re: [RFC PATCH v2 3/8] tools/nolibc: i386: Implement syscall with 6 arguments |
| |
On 3/22/22 6:39 PM, David Laight wrote: >> + __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"(eax) >> + : "a"(eax), "b"(ebx), "c"(ecx), "d"(edx), "S"(esi), "D"(edi), > > Does having "=a" for an output constraint and "a" for an input > constraint actually DTRT? > There is a special syntax for tying input and output to > the same register. > Or you could use "+a"(nr_rval) and 'return nr_rval'.
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?
-- Ammar Faizi
| |