Messages in this thread | | | From | David Laight <> | Subject | RE: [RFC PATCH v2 3/8] tools/nolibc: i386: Implement syscall with 6 arguments | Date | Tue, 22 Mar 2022 13:37:54 +0000 |
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From: Willy Tarreau > Sent: 22 March 2022 12:14 > > On Tue, Mar 22, 2022 at 07:02:53PM +0700, Ammar Faizi wrote: > > 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? > > Hmmm indeed that comes back to the existing constructs and is certainly > more in line with the rest of the code (plus it will not be affected by > -O0).
I'd add an 'always_inline' to the function. That will force inline even with -O0.
> I seem to remember a register allocation issue which kept me away from > implementing it this way on i386 back then, but given that my focus was > not as much on i386 as it was on other platforms, it's likely that I have > not insisted too much and not tried this one which looks like the way to > go to me.
dunno, 'asm' register variables are rather more horrid and should probably only be used (for asm statements) when there aren't suitable register constraints.
(I'm sure there is a comment about that in the gcc docs.)
David
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