Date: Sun, 02 Aug 2009 03:26:04 -0700 From: Julian Elischer <julian@elischer.org> To: FreeBSD Current <current@freebsd.org> Subject: Re: puzzling code in pcpu stuff Message-ID: <4A7569BC.2060406@elischer.org> In-Reply-To: <4A756214.8010002@elischer.org> References: <4A756214.8010002@elischer.org>
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Julian Elischer wrote: > I simplified the output of the preprocessor for a PCPU_SET(xx, newval) > (to look at it). > > I came down to: (after formatting) for i386.. > { > __typeof(((struct pcpu *)0)->pc_xx) __val; > struct __s > { > u_char __b[(((sizeof(__val)) < (4)) ? > (sizeof(__val)) : (4))]; > } __s; > > __val = (newval); /* aligned */ > > if (sizeof(__val) == 1 > || sizeof(__val) == 2 > || sizeof(__val) == 4) { > __s = *(struct __s *)(void *)&__val; > __asm volatile("mov %1,%%fs:%0" : "=m" > (*(struct __s *)(__builtin_offsetof( > struct pcpu, pc_xx))) : "r" (__s)); > } else { > *__extension__ ( > { > __typeof(__val) *__p; > __asm volatile("movl %%fs:%1,%0; > addl %2,%0" : "=r" (__p) : "m" > (*(struct pcpu *)(__builtin_offsetof(struct pcpu, pc_prvspace))), > "i" > (__builtin_offsetof(struct pcpu, pc_xx))); > __p; > }) = __val; > } > } p.s. I looked at the original source but I couldn't really work it out there either. > > having had my brain explode on this several times, > I can't figure out exactly what teh clause after the else is doing. well I know wht it appears to be doing fromt eh source but I can;t work out how.. __asm foo to explain it is missing.. > > anyone better at reading __asm better than me care to explain it in > simple words? (maybe it's just too late at night for me here) > > _______________________________________________ > freebsd-current@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-current > To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org"
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