[Qemu-devel] [PATCH v3 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>
---
 exec.c            | 6 ++++++
 include/qom/cpu.h | 4 ++++
 qom/cpu.c         | 9 +++++++++
 3 files changed, 19 insertions(+)

diff --git a/exec.c b/exec.c
index 9e076bc..14e7c76 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;
@@ -2049,6 +2050,11 @@ static void check_watchpoint(int offset, int len, MemTxAttrs attrs, int flags)
             wp->hitaddr = vaddr;
             wp->hitattrs = attrs;
             if (!cpu->watchpoint_hit) {
+                if (wp->flags & BP_CPU &&
+                    !cc->debug_check_watchpoint(cpu, wp)) {
+                    wp->flags &= ~BP_WATCHPOINT_HIT;
+                    continue;
+                }
                 cpu->watchpoint_hit = wp;
                 tb_check_watchpoint(cpu);
                 if (wp->flags & BP_STOP_BEFORE_ACCESS) {
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 035179c..984bc8d 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -64,6 +64,7 @@ typedef uint64_t vaddr;
 #define CPU_GET_CLASS(obj) OBJECT_GET_CLASS(CPUClass, (obj), TYPE_CPU)
 
 typedef struct CPUState CPUState;
+typedef struct CPUWatchpoint CPUWatchpoint;
 
 typedef void (*CPUUnassignedAccess)(CPUState *cpu, hwaddr addr,
                                     bool is_write, bool is_exec, int opaque,
@@ -106,6 +107,8 @@ 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: return true if the architectural
+ *       watchpoint whose address has matched should really fire.
  * @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 +168,7 @@ 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, CPUWatchpoint *wp);
     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..5a6a47e 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, CPUWatchpoint *wp)
+{
+    /* 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