MIPS: Respect the FCSR exception mask for `si_code'

Respect the FCSR exception mask when interpreting the IEEE 754 exception
condition to report with SIGFPE in `si_code', so as not to use one that
has been masked where a different one set in parallel caused the FPE
hardware exception to trigger.  As per the IEEE Std 754 the Inexact
exception can happen together with Overflow or Underflow.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9703/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 10 insertions, 1 deletions

diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 88f04f0d2d21..dbfa47cdc8c1 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -12,6 +12,7 @@
  * Copyright (C) 2000, 2001, 2012 MIPS Technologies, Inc.  All rights reserved.
  * Copyright (C) 2014, Imagination Technologies Ltd.
  */
+#include <linux/bitops.h>
 #include <linux/bug.h>
 #include <linux/compiler.h>
 #include <linux/context_tracking.h>
@@ -817,7 +818,15 @@ asmlinkage void do_fpe(struct pt_regs *regs, unsigned long fcr31)
                 process_fpemu_return(sig, fault_addr);
 
                 goto out;
-        } else if (fcr31 & FPU_CSR_INV_X)
+        }
+
+        /*
+         * Inexact can happen together with Overflow or Underflow.
+         * Respect the mask to deliver the correct exception.
+         */
+        fcr31 &= (fcr31 & FPU_CSR_ALL_E) <<
+                 (ffs(FPU_CSR_ALL_X) - ffs(FPU_CSR_ALL_E));
+        if (fcr31 & FPU_CSR_INV_X)
                 info.si_code = FPE_FLTINV;
         else if (fcr31 & FPU_CSR_DIV_X)
                 info.si_code = FPE_FLTDIV;