MIPS: Switch FPU emulator trap to BREAK instruction.

Arguably using the address error handler has always been ugly.  But with
processors that handle unaligned loads and stores in hardware the
current mechanism ceases to work so switch it to a BREAK instruction and
allocate break code 514 to the FPU emulator.

Yoichi Yuasa provided a build fix for CONFIG_BUG=n.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>

1 files changed, 16 insertions, 0 deletions

diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 3f6de76d485d..353056110f2b 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -32,6 +32,7 @@
 #include <asm/cpu.h>
 #include <asm/dsp.h>
 #include <asm/fpu.h>
+#include <asm/fpu_emulator.h>
 #include <asm/mipsregs.h>
 #include <asm/mipsmtregs.h>
 #include <asm/module.h>
@@ -722,6 +723,21 @@ static void do_trap_or_bp(struct pt_regs *regs, unsigned int code,
                 die_if_kernel("Kernel bug detected", regs);
                 force_sig(SIGTRAP, current);
                 break;
+        case BRK_MEMU:
+                /*
+                 * Address errors may be deliberately induced by the FPU
+                 * emulator to retake control of the CPU after executing the
+                 * instruction in the delay slot of an emulated branch.
+                 *
+                 * Terminate if exception was recognized as a delay slot return
+                 * otherwise handle as normal.
+                 */
+                if (do_dsemulret(regs))
+                        return;
+
+                die_if_kernel("Math emu break/trap", regs);
+                force_sig(SIGTRAP, current);
+                break;
         default:
                 scnprintf(b, sizeof(b), "%s instruction in kernel code", str);
                 die_if_kernel(b, regs);