signal/mips: Document a conflict with SI_USER with SIGFPE

Setting si_code to __SI_FAULT results in a userspace seeing
an si_code of 0.  This is the same si_code as SI_USER.  Posix
and common sense requires that SI_USER not be a signal specific
si_code.  As such this use of 0 for the si_code is a pretty
horribly broken ABI.

This use of of __SI_FAULT is only a decade old.  Which compared
to the other pieces of kernel code that has made this mistake
is almost yesterday.

This is probably worth fixing but I don't know mips well enough
to know what si_code to would be the proper one to use.

Cc: Ralf Baechle <ralf@linux-mips.org>
Ref: 948a34cf3988 ("[MIPS] Maintain si_code field properly for FP exceptions")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

diff --git a/arch/mips/include/uapi/asm/siginfo.h b/arch/mips/include/uapi/asm/siginfo.h
index 8069cf7..9becfd1 100644 (file)
--- a/arch/mips/include/uapi/asm/siginfo.h
+++ b/arch/mips/include/uapi/asm/siginfo.h
@@ -123,4 +123,11 @@ typedef struct siginfo {
 #define SI_TIMER __SI_CODE(__SI_TIMER, -3) /* sent by timer expiration */
 #define SI_MESGQ __SI_CODE(__SI_MESGQ, -4) /* sent by real time mesq state change */
 
+/*
+ * SIGFPE si_codes
+ */
+#ifdef __KERNEL__
+#define FPE_FIXME      (__SI_FAULT|0)  /* Broken dup of SI_USER */
+#endif /* __KERNEL__ */
+
 #endif /* _UAPI_ASM_SIGINFO_H */

diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index b68b4d0..6c9cca9 100644 (file)
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -735,7 +735,7 @@ void force_fcr31_sig(unsigned long fcr31, void __user *fault_addr,
        else if (fcr31 & FPU_CSR_INE_X)
                si.si_code = FPE_FLTRES;
        else
-               si.si_code = __SI_FAULT;
+               si.si_code = FPE_FIXME;
        force_sig_info(SIGFPE, &si, tsk);
 }