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Message-ID: <20071113194550.GA4400@Krystal> Date: Tue, 13 Nov 2007 14:45:50 -0500 From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> To: "H. Peter Anvin" <hpa@...or.com> Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, Andi Kleen <ak@....de>, Chuck Ebbert <cebbert@...hat.com>, Christoph Hellwig <hch@...radead.org>, Jeremy Fitzhardinge <jeremy@...p.org> Subject: Re: [patch 5/8] Immediate Values - x86 Optimization * H. Peter Anvin (hpa@...or.com) wrote: > Mathieu Desnoyers wrote: >>> - Use "=g" constraint for char immediate value inline assembly. >>> >>> "=g" is the same as "=rmi" which is inherently bogus. In your actual >>> code you use "=r", the correct constraint is "=q". >> q >> Any register accessible as rl. In 32-bit mode, a, b, c, and d; in >> 64-bit mode, any integer register. I am worried that "=q" might exclude >> the si and di registers in 32-bit mode. >> What exactly is wrong with "=r" ? > > For "char" (8-bit) values, sp/bp/si/di are illegal in 32-bit mode. > > Hence "=q". > Ah! yep, I see, so we say: 1 byte : "=q" 2 bytes : "=r" 4 bytes : "=r" 8 bytes : "=r" ? (si and di appear to be legal for 2 and 4 bytes in 32-bit mode) > -hpa -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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