This patch fixes a problem with incorrect floating-point exception
signal delivery on i386 kernels. In some cases, an error code of zero
is delivered instead of the correct code, as the output from my test
program shows:
Before patch:
$ ./fpsig
handler: signum = 8, errno = 0, code = 0
handler: fpu cwd = 0xb40, fpu swd = 0xbaa0
After:
$ ./fpsig
handler: signum = 8, errno = 0, code = 6
handler: fpu cwd = 0xb40, fpu swd = 0xbaa0
2.4 also has this problem; the patch applies with offsets on 2.4.31
but I didn't test it beyond that. Patch also applies to 2.6.13-rc6-mm1
with offsets.
x86-64 also looks to be affected but I have no way to test it
Test program:
/* i387 fp signal test */
#define _GNU_SOURCE
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>
#include <errno.h>
__attribute__ ((aligned(4096))) unsigned char altstack[4096];
unsigned short cw = 0x0b40; /* unmask all exceptions, round up */
struct sigaction sa;
stack_t ss = {
.ss_sp = &altstack[2047],
.ss_size = sizeof(altstack)/2,
};
static void handler(int nr, siginfo_t *si, void *uc)
{
printf("handler: signum = %d, errno = %d, code = %d\n",
si->si_signo, si->si_errno, si->si_code);
printf("handler: fpu cwd = 0x%hx, fpu swd = 0x%hx\n",
*(unsigned short *)&altstack[0xd84],
*(unsigned short *)&altstack[0xd88]);
exit(1);
}
int main(int argc, char * const argv[])
{
sa.sa_sigaction = handler;
sa.sa_flags = SA_ONSTACK | SA_SIGINFO;
if (sigaltstack(&ss, 0))
perror("sigaltstack");
if (sigaction(SIGFPE, &sa, NULL))
perror("sigaction");
asm volatile ("fnclex ; fldcw %0" : : "m" (cw));
asm volatile ( /* st(1) = 3.0, st = 1.0 */
"fld1 ; fld1 ; faddp ; fld1 ; faddp ; fld1");
asm volatile (
"fdivp ; fwait"); /* 1.0 / 3.0 */
return 0;
}
Signed-off-by: Chuck Ebbert <[EMAIL PROTECTED]>
arch/i386/kernel/traps.c | 8 ++++++--
1 files changed, 6 insertions(+), 2 deletions(-)
--- 2.6.13-rc6a.orig/arch/i386/kernel/traps.c
+++ 2.6.13-rc6a/arch/i386/kernel/traps.c
@@ -778,7 +778,7 @@ void math_error(void __user *eip)
{
struct task_struct * task;
siginfo_t info;
- unsigned short cwd, swd;
+ unsigned short cwd, swd, wd;
/*
* Save the info for the exception handler and clear the error.
@@ -803,7 +803,11 @@ void math_error(void __user *eip)
*/
cwd = get_fpu_cwd(task);
swd = get_fpu_swd(task);
- switch (((~cwd) & swd & 0x3f) | (swd & 0x240)) {
+ wd = swd & 0x3f & ~cwd;
+ if (wd & 1)
+ wd |= swd & 0x240;
+
+ switch (wd) {
case 0x000:
default:
break;
__
Chuck
-
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