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x86: prioritize the FPU traps for the error code

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In the case of multiple FPU errors, prioritize the error codes,
instead of returning __SI_FAULT, which ends up pushing a 0 as the
error code to userspace, a POSIX violation.

For i386, we will simply return if there are no errors at all; for
x86-64 this is probably a "can't happen" (and the code should be
unified), but for this patch, return __SI_FAULT|SI_KERNEL if this ever
happens.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
H. Peter Anvin 2008-12-22 17:56:05 -08:00
parent 55dac3a555
commit adf77bac05
1 changed files with 15 additions and 19 deletions
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34
arch/x86/kernel/traps.c
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@ -664,7 +664,7 @@ void math_error(void __user *ip)
{
struct task_struct *task;
siginfo_t info;
unsigned short cwd, swd;
unsigned short cwd, swd, err;
/*
* Save the info for the exception handler and clear the error.
@ -675,7 +675,6 @@ void math_error(void __user *ip)
task->thread.error_code = 0;
info.si_signo = SIGFPE;
info.si_errno = 0;
info.si_code = __SI_FAULT;
info.si_addr = ip;
/*
* (~cwd & swd) will mask out exceptions that are not set to unmasked
@ -689,34 +688,31 @@ void math_error(void __user *ip)
*/
cwd = get_fpu_cwd(task);
swd = get_fpu_swd(task);
switch (swd & ~cwd & 0x3f) {
case 0x000: /* No unmasked exception */
#ifdef CONFIG_X86_32
err = swd & ~cwd & 0x3f;
#if CONFIG_X86_32
if (!err)
return;
#endif
default: /* Multiple exceptions */
break;
case 0x001: /* Invalid Op */
if (err & 0x001) { /* Invalid op */
/*
* swd & 0x240 == 0x040: Stack Underflow
* swd & 0x240 == 0x240: Stack Overflow
* User must clear the SF bit (0x40) if set
*/
info.si_code = FPE_FLTINV;
break;
case 0x002: /* Denormalize */
case 0x010: /* Underflow */
info.si_code = FPE_FLTUND;
break;
case 0x004: /* Zero Divide */
} else if (err & 0x004) { /* Divide by Zero */
info.si_code = FPE_FLTDIV;
break;
case 0x008: /* Overflow */
} else if (err & 0x008) { /* Overflow */
info.si_code = FPE_FLTOVF;
break;
case 0x020: /* Precision */
} else if (err & 0x012) { /* Denormal, Underflow */
info.si_code = FPE_FLTUND;
} else if (err & 0x020) { /* Precision */
info.si_code = FPE_FLTRES;
break;
} else {
info.si_code = __SI_FAULT|SI_KERNEL; /* WTF? */
}
force_sig_info(SIGFPE, &info, task);
}