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Commit dd570237 authored by Anton Blanchard's avatar Anton Blanchard Committed by Michael Ellerman
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powerpc: Improve comment explaining why we modify VRSAVE 



The comment explaining why we modify VRSAVE is misleading, glibc
does rely on the behaviour. Update the comment.

Signed-off-by: default avatarAnton Blanchard <anton@samba.org>
Reviewed-by: default avatarCyril Bur <cyrilbur@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 1a1cee84

arch/powerpc/kernel/vector.S

+5 −4
Original line number Diff line number Diff line
@@ -70,10 +70,11 @@ _GLOBAL(load_up_altivec) 
	MTMSRD(r5)			/* enable use of AltiVec now */

	isync



	/* Hack: if we get an altivec unavailable trap with VRSAVE

	 * set to all zeros, we assume this is a broken application

	 * that fails to set it properly, and thus we switch it to

	 * all 1's

	/*

	 * While userspace in general ignores VRSAVE, glibc uses it as a boolean

	 * to optimise userspace context save/restore. Whenever we take an

	 * altivec unavailable exception we must set VRSAVE to something non

	 * zero. Set it to all 1s. See also the programming note in the ISA.

	 */

	mfspr	r4,SPRN_VRSAVE

	cmpwi	0,r4,0