Date: Tue, 26 Jan 2016 18:39:23 +0000 (UTC) From: Warner Losh <imp@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r294846 - head/sys/mips/mips Message-ID: <201601261839.u0QIdNKO019391@repo.freebsd.org>
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Author: imp Date: Tue Jan 26 18:39:23 2016 New Revision: 294846 URL: https://svnweb.freebsd.org/changeset/base/294846 Log: Add a comment about why at is turned off in the exception handler. Only k0 and k1 may be touched until we save registers somewhere. MFC After: 2 days Modified: head/sys/mips/mips/exception.S Modified: head/sys/mips/mips/exception.S ============================================================================== --- head/sys/mips/mips/exception.S Tue Jan 26 18:32:48 2016 (r294845) +++ head/sys/mips/mips/exception.S Tue Jan 26 18:39:23 2016 (r294846) @@ -177,6 +177,12 @@ MipsDoTLBMiss: VECTOR(MipsException, unknown) /* * Find out what mode we came from and jump to the proper handler. + * + * Note: at turned off here because we cannot trash the at register + * in this exception code. Only k0 and k1 may be modified before + * we save registers. This is true of all functions called through + * the pointer magic: Mips{User,Kern}Intr, Mips{User,Kern}GenException + * and MipsTLBInvalidException */ .set noat mfc0 k0, MIPS_COP_0_STATUS # Get the status register
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