[PATCH] x86-64: Fix incorrect FP signals

This is the same patch that went into i386 just before 2.6.13
came out.  I still can't build 64-bit user apps, so I tested
with program (see below) in 32-bit mode on 64-bit kernel:

Before:

	$ fpsig
	handler: nr = 8, si = 0x0804bc90, vuc = 0x0804bd10
	handler: altstack is at 0x0804b000, ebp = 0x0804bc7c
	handler: si_signo = 8, si_errno = 0, si_code = 0 [unknown]
	handler: fpu cwd = 0xb40, fpu swd = 0xbaa0
	handler: i387 unmasked precision exception, rounded up

After:

	$ fpsig
	handler: nr = 8, si = 0x0804bc90, vuc = 0x0804bd10
	handler: altstack is at 0x0804b000, ebp = 0x0804bc7c
	handler: si_signo = 8, si_errno = 0, si_code = 6 [inexact result]
	handler: fpu cwd = 0xb40, fpu swd = 0xbaa0
	handler: i387 unmasked precision exception, rounded up

Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 6 insertions, 3 deletions

diff --git a/arch/x86_64/kernel/traps.c b/arch/x86_64/kernel/traps.c
index 64a59cb4941..77658f7f4e8 100644
--- a/arch/x86_64/kernel/traps.c
+++ b/arch/x86_64/kernel/traps.c
@@ -795,13 +795,16 @@ asmlinkage void do_coprocessor_error(struct pt_regs *regs)
          */
         cwd = get_fpu_cwd(task);
         swd = get_fpu_swd(task);
-        switch (((~cwd) & swd & 0x3f) | (swd & 0x240)) {
+        switch (swd & ~cwd & 0x3f) {
                 case 0x000:
                 default:
                         break;
                 case 0x001: /* Invalid Op */
-                case 0x041: /* Stack Fault */
-                case 0x241: /* Stack Fault | Direction */
+                        /*
+                         * 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 */