[Qemu-devel] [PATCH 7/13] Restore pc on watchpoint hits

[Jan Kiszka <jan.kiszka@siemens.com>]

In order to provide accurate information about the triggering
instruction, this patch adds the required bits to restore the pc if the
access happened inside a TB. With the BP_STOP_BEFORE_ACCESS flag, the
watchpoint user can control if the debug trap should be issued on or
after the accessing instruction.

In contrast to the earlier posted version, this one makes use of
next_cflags to ensure that the next TB contains just a single
instruction.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 cpu-all.h |    1 +
 exec.c    |   22 ++++++++++++++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)

Index: b/exec.c
===================================================================
--- a/exec.c
+++ b/exec.c
@@ -2385,16 +2385,34 @@ static CPUWriteMemoryFunc *notdirty_mem_
 static void check_watchpoint(int offset, int len_mask, int flags)
 {
     CPUState *env = cpu_single_env;
+    TranslationBlock *tb;
     target_ulong vaddr;
     CPUWatchpoint *wp;
 
+    if (env->watchpoint_hit) {
+        /* We re-entered the check after replacing the TB. Now raise
+         * the debug interrupt so that is will trigger after the
+         * current instruction. */
+        cpu_interrupt(env, CPU_INTERRUPT_DEBUG);
+        return;
+    }
     vaddr = (env->mem_io_vaddr & TARGET_PAGE_MASK) + offset;
     for (wp = env->watchpoints; wp != NULL; wp = wp->next) {
         if ((vaddr == (wp->vaddr & len_mask) ||
              (vaddr & wp->len_mask) == wp->vaddr) && (wp->flags & flags)) {
             env->watchpoint_hit = wp;
-            cpu_interrupt(env, CPU_INTERRUPT_DEBUG);
-            break;
+            tb = tb_find_pc(env->mem_io_pc);
+            if (!tb) {
+                cpu_abort(env, "check_watchpoint: could not find TB for pc=%p",
+                         (void *)env->mem_io_pc);
+            }
+            cpu_restore_state(tb, env, env->mem_io_pc, NULL);
+            tb_phys_invalidate(tb, -1);
+            if (wp->flags & BP_STOP_BEFORE_ACCESS)
+                env->exception_index = EXCP_DEBUG;
+            else
+                env->next_cflags = 1;
+            cpu_resume_from_signal(env, NULL);
         }
     }
 }
Index: b/cpu-all.h
===================================================================
--- a/cpu-all.h
+++ b/cpu-all.h
@@ -803,6 +803,7 @@ void cpu_reset_interrupt(CPUState *env,
 #define BP_MEM_READ           0x01
 #define BP_MEM_WRITE          0x02
 #define BP_MEM_ACCESS         (BP_MEM_READ | BP_MEM_WRITE)
+#define BP_STOP_BEFORE_ACCESS 0x04
 #define BP_GDB                0x10
 
 int cpu_breakpoint_insert(CPUState *env, target_ulong pc, int flags,