Fix incorrect FP signals From: Chuck Ebbert <76306.1226@compuserve.com> 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> arch/x86_64/kernel/traps.c | 9 ++++++--- 1 files changed, 6 insertions(+), 3 deletions(-) Signed-off-by: Andi Kleen Index: linux/arch/x86_64/kernel/traps.c =================================================================== --- linux.orig/arch/x86_64/kernel/traps.c +++ linux/arch/x86_64/kernel/traps.c @@ -795,13 +795,16 @@ asmlinkage void do_coprocessor_error(str */ 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 */