plugins: save value during memory accesses

Different code paths handle memory accesses:
- tcg generated code
- load/store helpers
- atomic helpers

This value is saved in cpu->neg.plugin_mem_value_{high,low}. Values are
written only for accessed word size (upper bits are not set).

Atomic operations are doing read/write at the same time, so we generate
two memory callbacks instead of one, to allow plugins to access distinct
values.

For now, we can have access only up to 128 bits, thus split this in two
64 bits words. When QEMU will support wider operations, we'll be able to
reconsider this.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-Id: <20240724194708.1843704-2-pierrick.bouvier@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240916085400.1046925-5-alex.bennee@linaro.org>

accel/tcg/atomic_common.c.inc

@@ -14,9 +14,20 @@
  */
 
 static void atomic_trace_rmw_post(CPUArchState *env, uint64_t addr,
+                                  uint64_t read_value_low,
+                                  uint64_t read_value_high,
+                                  uint64_t write_value_low,
+                                  uint64_t write_value_high,
                                   MemOpIdx oi)
 {
-    qemu_plugin_vcpu_mem_cb(env_cpu(env), addr, oi, QEMU_PLUGIN_MEM_RW);
+    if (cpu_plugin_mem_cbs_enabled(env_cpu(env))) {
+        qemu_plugin_vcpu_mem_cb(env_cpu(env), addr,
+                                read_value_low, read_value_high,
+                                oi, QEMU_PLUGIN_MEM_R);
+        qemu_plugin_vcpu_mem_cb(env_cpu(env), addr,
+                                write_value_low, write_value_high,
+                                oi, QEMU_PLUGIN_MEM_W);
+    }
 }
 
 /*