Date: Sat, 1 Sep 2012 15:55:14 +0000 (UTC) From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-9@freebsd.org Subject: svn commit: r239994 - stable/9/sys/i386/isa Message-ID: <201209011555.q81FtEEA033983@svn.freebsd.org>
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Author: kib Date: Sat Sep 1 15:55:14 2012 New Revision: 239994 URL: http://svn.freebsd.org/changeset/base/239994 Log: MFC r238677: Stop clearing x87 exceptions in the #MF handler. Modified: stable/9/sys/i386/isa/npx.c Directory Properties: stable/9/sys/ (props changed) Modified: stable/9/sys/i386/isa/npx.c ============================================================================== --- stable/9/sys/i386/isa/npx.c Sat Sep 1 15:53:26 2012 (r239993) +++ stable/9/sys/i386/isa/npx.c Sat Sep 1 15:55:14 2012 (r239994) @@ -583,21 +583,21 @@ static char fpetable[128] = { }; /* - * Preserve the FP status word, clear FP exceptions, then generate a SIGFPE. + * Read the FP status and control words, then generate si_code value + * for SIGFPE. The error code chosen will be one of the + * FPE_... macros. It will be sent as the second argument to old + * BSD-style signal handlers and as "siginfo_t->si_code" (second + * argument) to SA_SIGINFO signal handlers. * - * Clearing exceptions is necessary mainly to avoid IRQ13 bugs. We now - * depend on longjmp() restoring a usable state. Restoring the state - * or examining it might fail if we didn't clear exceptions. + * Some time ago, we cleared the x87 exceptions with FNCLEX there. + * Clearing exceptions was necessary mainly to avoid IRQ13 bugs. The + * usermode code which understands the FPU hardware enough to enable + * the exceptions, can also handle clearing the exception state in the + * handler. The only consequence of not clearing the exception is the + * rethrow of the SIGFPE on return from the signal handler and + * reexecution of the corresponding instruction. * - * The error code chosen will be one of the FPE_... macros. It will be - * sent as the second argument to old BSD-style signal handlers and as - * "siginfo_t->si_code" (second argument) to SA_SIGINFO signal handlers. - * - * XXX the FP state is not preserved across signal handlers. So signal - * handlers cannot afford to do FP unless they preserve the state or - * longjmp() out. Both preserving the state and longjmp()ing may be - * destroyed by IRQ13 bugs. Clearing FP exceptions is not an acceptable - * solution for signals other than SIGFPE. + * For XMM traps, the exceptions were never cleared. */ int npxtrap() @@ -623,9 +623,6 @@ npxtrap() fnstcw(&control); fnstsw(&status); } - - if (PCPU_GET(fpcurthread) == curthread) - fnclex(); critical_exit(); return (fpetable[status & ((~control & 0x3f) | 0x40)]); }
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