[PATCH v2 33/35] tcg: exclude non-memory effecting helpers from instrumentation

[Alex Bennée]

From: Emilio Cota <cota@braap.org>

There are actually a whole bunch of helpers that don't affect memory
that we shouldn't instrument. They are helpfully identified by the
TCG_CALL_NO_SIDE_EFFECTS flag which marks out lookup_tb_ptr as well as
a lot of the maths helpers. To avoid the string compare we introduce a
new flag for plugin internals so we skip that too.

Related: #1381
Signed-off-by: Emilio Cota <cota@braap.org>
Message-Id: <20230108164731.61469-4-cota@braap.org>
[AJB: updated to skip all no SE plugins, add flag for plugin helper]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

---
v2
  - use TCG_CALL_NO_SIDE_EFFECTS as suggested by rth
  - add flag for plugin specific helpers
---
 accel/tcg/plugin-helpers.h | 4 ++--
 include/tcg/tcg.h          | 2 ++
 tcg/tcg.c                  | 6 ++++--
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/accel/tcg/plugin-helpers.h b/accel/tcg/plugin-helpers.h
index 9829abe4a9..8e685e0654 100644
--- a/accel/tcg/plugin-helpers.h
+++ b/accel/tcg/plugin-helpers.h
@@ -1,4 +1,4 @@
 #ifdef CONFIG_PLUGIN
-DEF_HELPER_FLAGS_2(plugin_vcpu_udata_cb, TCG_CALL_NO_RWG, void, i32, ptr)
-DEF_HELPER_FLAGS_4(plugin_vcpu_mem_cb, TCG_CALL_NO_RWG, void, i32, i32, i64, 
ptr)
+DEF_HELPER_FLAGS_2(plugin_vcpu_udata_cb, TCG_CALL_NO_RWG | TCG_CALL_PLUGIN, 
void, i32, ptr)
+DEF_HELPER_FLAGS_4(plugin_vcpu_mem_cb, TCG_CALL_NO_RWG | TCG_CALL_PLUGIN, 
void, i32, i32, i64, ptr)
 #endif
diff --git a/include/tcg/tcg.h b/include/tcg/tcg.h
index 6f497172f8..8dc291d030 100644
--- a/include/tcg/tcg.h
+++ b/include/tcg/tcg.h
@@ -405,6 +405,8 @@ typedef TCGv_ptr TCGv_env;
 #define TCG_CALL_NO_SIDE_EFFECTS    0x0004
 /* Helper is G_NORETURN.  */
 #define TCG_CALL_NO_RETURN          0x0008
+/* Helper is part of Plugins.  */
+#define TCG_CALL_PLUGIN             0x0010
 
 /* convenience version of most used call flags */
 #define TCG_CALL_NO_RWG         TCG_CALL_NO_READ_GLOBALS
diff --git a/tcg/tcg.c b/tcg/tcg.c
index d502327be2..fd557d55d3 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -1674,8 +1674,10 @@ void tcg_gen_callN(void *func, TCGTemp *ret, int nargs, 
TCGTemp **args)
     op = tcg_op_alloc(INDEX_op_call, total_args);
 
 #ifdef CONFIG_PLUGIN
-    /* detect non-plugin helpers */
-    if (tcg_ctx->plugin_insn && unlikely(strncmp(info->name, "plugin_", 7))) {
+    /* Flag helpers that may affect guest state */
+    if (tcg_ctx->plugin_insn &&
+        !(info->flags & TCG_CALL_PLUGIN) &&
+        !(info->flags & TCG_CALL_NO_SIDE_EFFECTS)) {
         tcg_ctx->plugin_insn->calls_helpers = true;
     }
 #endif
-- 
2.34.1