[Qemu-devel] [PATCH v2 1/2] cpu: Add callback to check architectural watchpoint match

[Sergey Fedorov <serge.fdrv@gmail.com>]

When QEMU watchpoint matches, that is not definitely an architectural
watchpoint match yet. If it is a stop-before-access watchpoint then that
is hardly possible to ignore it after throwing a TCG exception.

A special callback is introduced to check for architectural watchpoint
match before raising a TCG exception.

Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
---

Notes:
    Changes in v2:
     * Check moved before setting cpu->watchpoint_hit
     * Pointer to watchpoint being checked passed to debug_check_watchpoint()
       callback
     * Comment for debug_check_watchpoint() callback improved

 exec.c            | 5 +++++
 include/qom/cpu.h | 3 +++
 qom/cpu.c         | 9 +++++++++
 3 files changed, 17 insertions(+)

diff --git a/exec.c b/exec.c
index 9e076bc..a20f8ea 100644
--- a/exec.c
+++ b/exec.c
@@ -2024,6 +2024,7 @@ static const MemoryRegionOps notdirty_mem_ops = {
 static void check_watchpoint(int offset, int len, MemTxAttrs attrs, int flags)
 {
     CPUState *cpu = current_cpu;
+    CPUClass *cc = CPU_GET_CLASS(cpu);
     CPUArchState *env = cpu->env_ptr;
     target_ulong pc, cs_base;
     target_ulong vaddr;
@@ -2050,6 +2051,10 @@ static void check_watchpoint(int offset, int len, MemTxAttrs attrs, int flags)
             wp->hitattrs = attrs;
             if (!cpu->watchpoint_hit) {
                 cpu->watchpoint_hit = wp;
+                if (wp->flags & BP_CPU && !cc->debug_check_watchpoint(cpu)) {
+                    cpu->watchpoint_hit = NULL;
+                    continue;
+                }
                 tb_check_watchpoint(cpu);
                 if (wp->flags & BP_STOP_BEFORE_ACCESS) {
                     cpu->exception_index = EXCP_DEBUG;
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 035179c..095ba08 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -106,6 +106,8 @@ struct TranslationBlock;
  *       a memory access with the specified memory transaction attributes.
  * @gdb_read_register: Callback for letting GDB read a register.
  * @gdb_write_register: Callback for letting GDB write a register.
+ * @debug_check_watchpoint: Callback for checking an architectural watchpoint
+ * match.
  * @debug_excp_handler: Callback for handling debug exceptions.
  * @write_elf64_note: Callback for writing a CPU-specific ELF note to a
  * 64-bit VM coredump.
@@ -165,6 +167,7 @@ typedef struct CPUClass {
     int (*asidx_from_attrs)(CPUState *cpu, MemTxAttrs attrs);
     int (*gdb_read_register)(CPUState *cpu, uint8_t *buf, int reg);
     int (*gdb_write_register)(CPUState *cpu, uint8_t *buf, int reg);
+    bool (*debug_check_watchpoint)(CPUState *cpu);
     void (*debug_excp_handler)(CPUState *cpu);
 
     int (*write_elf64_note)(WriteCoreDumpFunction f, CPUState *cpu,
diff --git a/qom/cpu.c b/qom/cpu.c
index 8f537a4..5caa0ee 100644
--- a/qom/cpu.c
+++ b/qom/cpu.c
@@ -188,6 +188,14 @@ static int cpu_common_gdb_write_register(CPUState *cpu, uint8_t *buf, int reg)
     return 0;
 }
 
+static bool cpu_common_debug_check_watchpoint(CPUState *cpu)
+{
+    /* If no extra check is required, QEMU watchpoint match can be considered
+     * as an architectural match.
+     */
+    return true;
+}
+
 bool target_words_bigendian(void);
 static bool cpu_common_virtio_is_big_endian(CPUState *cpu)
 {
@@ -352,6 +360,7 @@ static void cpu_class_init(ObjectClass *klass, void *data)
     k->gdb_write_register = cpu_common_gdb_write_register;
     k->virtio_is_big_endian = cpu_common_virtio_is_big_endian;
     k->debug_excp_handler = cpu_common_noop;
+    k->debug_check_watchpoint = cpu_common_debug_check_watchpoint;
     k->cpu_exec_enter = cpu_common_noop;
     k->cpu_exec_exit = cpu_common_noop;
     k->cpu_exec_interrupt = cpu_common_exec_interrupt;
-- 
1.9.1