MIPS: Watch exception handling for HARDWARE_WATCHPOINTS.

Here we hook up the watch exception handler so that it sends SIGTRAP when
the hardware watch registers are triggered.

Signed-off-by: David Daney <ddaney@avtrex.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

2 files changed, 23 insertions, 5 deletions

diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S
index 01dcbe38fa01..757d48f0d80f 100644
--- a/arch/mips/kernel/genex.S
+++ b/arch/mips/kernel/genex.S
@@ -453,7 +453,11 @@ NESTED(nmi_handler, PT_SIZE, sp)
         BUILD_HANDLER tr tr sti silent                  /* #13 */
         BUILD_HANDLER fpe fpe fpe silent                /* #15 */
         BUILD_HANDLER mdmx mdmx sti silent              /* #22 */
+#ifdef  CONFIG_HARDWARE_WATCHPOINTS
+        BUILD_HANDLER watch watch sti silent            /* #23 */
+#else
         BUILD_HANDLER watch watch sti verbose           /* #23 */
+#endif
         BUILD_HANDLER mcheck mcheck cli verbose         /* #24 */
         BUILD_HANDLER mt mt sti silent                  /* #25 */
         BUILD_HANDLER dsp dsp sti silent                /* #26 */
diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index b602ac6eb47d..80b9e070c207 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -42,6 +42,7 @@
 #include <asm/tlbdebug.h>
 #include <asm/traps.h>
 #include <asm/uaccess.h>
+#include <asm/watch.h>
 #include <asm/mmu_context.h>
 #include <asm/types.h>
 #include <asm/stacktrace.h>
@@ -912,13 +913,26 @@ asmlinkage void do_mdmx(struct pt_regs *regs)
 
 asmlinkage void do_watch(struct pt_regs *regs)
 {
+        u32 cause;
+
         /*
-         * We use the watch exception where available to detect stack
-         * overflows.
+         * Clear WP (bit 22) bit of cause register so we don't loop
+         * forever.
          */
-        dump_tlb_all();
-        show_regs(regs);
-        panic("Caught WATCH exception - probably caused by stack overflow.");
+        cause = read_c0_cause();
+        cause &= ~(1 << 22);
+        write_c0_cause(cause);
+
+        /*
+         * If the current thread has the watch registers loaded, save
+         * their values and send SIGTRAP.  Otherwise another thread
+         * left the registers set, clear them and continue.
+         */
+        if (test_tsk_thread_flag(current, TIF_LOAD_WATCH)) {
+                mips_read_watch_registers();
+                force_sig(SIGTRAP, current);
+        } else
+                mips_clear_watch_registers();
 }
 
 asmlinkage void do_mcheck(struct pt_regs *regs)