Date: Thu, 22 Nov 2001 16:43:34 +0800 From: "David Xu" <davidx@viasoft.com.cn> To: "John Baldwin" <jhb@FreeBSD.org> Cc: <freebsd-hackers@FreeBSD.org> Subject: Re: add some constraints in cpufunc.h Message-ID: <005201c17331$c603bcd0$ef01a8c0@davidwnt> References: <XFMail.011121113835.jhb@FreeBSD.org>
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According to GCC manual of inline assembler instruction, it says if = your instruction changes condition code register(on X86, it's cpu flag register, and a = simple addl=20 instruction can affect it), you'd put cc there, I have reviewed some = source header files of bus management, they all have cc constraint, but others not, = and some=20 lines lost __volatile__ keyword, GCC can feel free to optimize them = and re-order=20 or delete these lines when it thinks this is a right decision, this = could be dangerous when high optimizing option is turned on. -- David Xu ----- Original Message -----=20 From: "John Baldwin" <jhb@FreeBSD.org> To: "David Xu" <davidx@viasoft.com.cn> Cc: <freebsd-hackers@FreeBSD.org> Sent: Thursday, November 22, 2001 3:38 AM Subject: RE: add some constraints in cpufunc.h >=20 > On 21-Nov-01 David Xu wrote: > > 4.4-stable, file sys/i386/include/cpufunc.h,=20 > >=20 > > --- cpufunc.h.orig Wed Nov 21 13:35:36 2001 > > +++ cpufunc.h Wed Nov 21 15:00:12 2001 > > @@ -72,7 +72,7 @@ > > { > > u_int result; > > =20 > > - __asm __volatile("bsfl %0,%0" : "=3Dr" (result) : "0" = (mask)); > > + __asm __volatile("bsfl %0,%0" : "=3Dr" (result) : "0" (mask) = : "cc"); > > return (result); > > } > > =20 > > @@ -81,7 +81,7 @@ > > { > > u_int result; > > =20 > > - __asm __volatile("bsrl %0,%0" : "=3Dr" (result) : "0" = (mask)); > > + __asm __volatile("bsrl %0,%0" : "=3Dr" (result) : "0" (mask) = : "cc"); > > return (result); > > } > > =20 > > @@ -305,7 +305,7 @@ > > u_int result; > > =20 > > __asm __volatile("xorl %0,%0; xchgl %1,%0" > > - : "=3D&r" (result) : "m" (*addr)); > > + : "=3D&r" (result) : "m" (*addr) : "cc"); > > return (result); > > } > >=20 >=20 > Have you had actual bugs as a result of "cc" not being in the = constraints? >=20 > If so, there's a _lot_ more places that need this. All the atomic = ops, for > example. >=20 > --=20 >=20 > John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ > "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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