Messages in this thread | | | Date | Fri, 20 Dec 2002 15:50:37 -0800 | From | "H. Peter Anvin" <> | Subject | Re: Intel P6 vs P7 system call performance |
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Jamie Lokier wrote: > > No, your "real" code sequence is wrong. > > %ebx/%edi/%esi are preserved across sysenter/sysexit, whereas > %ecx/%edx are call-clobbered registers in the i386 function call ABI. > > This is not a coincidence. > > So, getpid looks like this with the _smaller_ vsyscall code: > > getpid(): > movl $__NR_getpid,%eax > call *%gs:0x18 > ret
... or just...
getpid: movl $__NR_getpid, %eax jmp *%gs:0x18
This doesn't mess up the call/return stack, even, because the ret in the stub matches the call to getpid.
-hpa
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