plugins: extend API to get latest memory value accessed

This value can be accessed only during a memory callback, using
new qemu_plugin_mem_get_value function.

Returned value can be extended when QEMU will support accesses wider
than 128 bits.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1719
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2152
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Xingtao Yao <yaoxt.fnst@fujitsu.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-Id: <20240724194708.1843704-3-pierrick.bouvier@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240916085400.1046925-6-alex.bennee@linaro.org>

include/qemu/qemu-plugin.h

@@ -262,6 +262,29 @@ enum qemu_plugin_mem_rw {
     QEMU_PLUGIN_MEM_RW,
 };
 
+enum qemu_plugin_mem_value_type {
+    QEMU_PLUGIN_MEM_VALUE_U8,
+    QEMU_PLUGIN_MEM_VALUE_U16,
+    QEMU_PLUGIN_MEM_VALUE_U32,
+    QEMU_PLUGIN_MEM_VALUE_U64,
+    QEMU_PLUGIN_MEM_VALUE_U128,
+};
+
+/* typedef qemu_plugin_mem_value - value accessed during a load/store */
+typedef struct {
+    enum qemu_plugin_mem_value_type type;
+    union {
+        uint8_t u8;
+        uint16_t u16;
+        uint32_t u32;
+        uint64_t u64;
+        struct {
+            uint64_t low;
+            uint64_t high;
+        } u128;
+    } data;
+} qemu_plugin_mem_value;
+
 /**
  * enum qemu_plugin_cond - condition to enable callback
  *
@@ -551,6 +574,15 @@ bool qemu_plugin_mem_is_big_endian(qemu_plugin_meminfo_t info);
 QEMU_PLUGIN_API
 bool qemu_plugin_mem_is_store(qemu_plugin_meminfo_t info);
 
+/**
+ * qemu_plugin_mem_get_mem_value() - return last value loaded/stored
+ * @info: opaque memory transaction handle
+ *
+ * Returns: memory value
+ */
+QEMU_PLUGIN_API
+qemu_plugin_mem_value qemu_plugin_mem_get_value(qemu_plugin_meminfo_t info);
+
 /**
  * qemu_plugin_get_hwaddr() - return handle for memory operation
  * @info: opaque memory info structure

plugins/api.c

@@ -351,6 +351,39 @@ bool qemu_plugin_mem_is_store(qemu_plugin_meminfo_t info)
     return get_plugin_meminfo_rw(info) & QEMU_PLUGIN_MEM_W;
 }
 
+qemu_plugin_mem_value qemu_plugin_mem_get_value(qemu_plugin_meminfo_t info)
+{
+    uint64_t low = current_cpu->neg.plugin_mem_value_low;
+    qemu_plugin_mem_value value;
+
+    switch (qemu_plugin_mem_size_shift(info)) {
+    case 0:
+        value.type = QEMU_PLUGIN_MEM_VALUE_U8;
+        value.data.u8 = (uint8_t)low;
+        break;
+    case 1:
+        value.type = QEMU_PLUGIN_MEM_VALUE_U16;
+        value.data.u16 = (uint16_t)low;
+        break;
+    case 2:
+        value.type = QEMU_PLUGIN_MEM_VALUE_U32;
+        value.data.u32 = (uint32_t)low;
+        break;
+    case 3:
+        value.type = QEMU_PLUGIN_MEM_VALUE_U64;
+        value.data.u64 = low;
+        break;
+    case 4:
+        value.type = QEMU_PLUGIN_MEM_VALUE_U128;
+        value.data.u128.low = low;
+        value.data.u128.high = current_cpu->neg.plugin_mem_value_high;
+        break;
+    default:
+        g_assert_not_reached();
+    }
+    return value;
+}
+
 /*
  * Virtual Memory queries
  */

plugins/qemu-plugins.symbols

@@ -13,6 +13,7 @@
   qemu_plugin_insn_size;
   qemu_plugin_insn_symbol;
   qemu_plugin_insn_vaddr;
+  qemu_plugin_mem_get_value;
   qemu_plugin_mem_is_big_endian;
   qemu_plugin_mem_is_sign_extended;
   qemu_plugin_mem_is_store;