plugins: try and make plugin_insn_append more ergonomic

Currently we make the assumption that the guest frontend loads all
op code bytes sequentially. This mostly holds up for regular fixed
encodings but some architectures like s390x like to re-read the
instruction which causes weirdness to occur. Rather than changing the
frontends make the plugin API a little more ergonomic and able to
handle the re-read case.

Stuff will still get strange if we read ahead of the opcode but so far
no front ends have done that and this patch asserts the case so we can
catch it early if they do.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20211026102234.3961636-21-alex.bennee@linaro.org>

4 files changed, 17 insertions, 7 deletions

diff --git a/accel/tcg/plugin-gen.c b/accel/tcg/plugin-gen.c
index 61be64b78c..22d95fe1c3 100644
--- a/accel/tcg/plugin-gen.c
+++ b/accel/tcg/plugin-gen.c
@@ -876,9 +876,8 @@ void plugin_gen_insn_start(CPUState *cpu, const DisasContextBase *db)
     struct qemu_plugin_tb *ptb = tcg_ctx->plugin_tb;
     struct qemu_plugin_insn *pinsn;
 
-    pinsn = qemu_plugin_tb_insn_get(ptb);
+    pinsn = qemu_plugin_tb_insn_get(ptb, db->pc_next);
     tcg_ctx->plugin_insn = pinsn;
-    pinsn->vaddr = db->pc_next;
     plugin_gen_empty_callback(PLUGIN_GEN_FROM_INSN);
 
     /*
diff --git a/accel/tcg/translator.c b/accel/tcg/translator.c
index 390bd9db0a..f06c314266 100644
--- a/accel/tcg/translator.c
+++ b/accel/tcg/translator.c
@@ -169,7 +169,7 @@ static inline void translator_maybe_page_protect(DisasContextBase *dcbase,
         if (do_swap) {                                                  \
             ret = swap_fn(ret);                                         \
         }                                                               \
-        plugin_insn_append(&ret, sizeof(ret));                          \
+        plugin_insn_append(pc, &ret, sizeof(ret));                      \
         return ret;                                                     \
     }
 
diff --git a/include/exec/plugin-gen.h b/include/exec/plugin-gen.h
index b1b72b5d90..f92f169739 100644
--- a/include/exec/plugin-gen.h
+++ b/include/exec/plugin-gen.h
@@ -27,13 +27,21 @@ void plugin_gen_insn_end(void);
 void plugin_gen_disable_mem_helpers(void);
 void plugin_gen_empty_mem_callback(TCGv addr, uint32_t info);
 
-static inline void plugin_insn_append(const void *from, size_t size)
+static inline void plugin_insn_append(abi_ptr pc, const void *from, size_t size)
 {
     struct qemu_plugin_insn *insn = tcg_ctx->plugin_insn;
+    abi_ptr off;
 
     if (insn == NULL) {
         return;
     }
+    off = pc - insn->vaddr;
+    if (off < insn->data->len) {
+        g_byte_array_set_size(insn->data, off);
+    } else if (off > insn->data->len) {
+        /* we have an unexpected gap */
+        g_assert_not_reached();
+    }
 
     insn->data = g_byte_array_append(insn->data, from, size);
 }
@@ -62,7 +70,7 @@ static inline void plugin_gen_disable_mem_helpers(void)
 static inline void plugin_gen_empty_mem_callback(TCGv addr, uint32_t info)
 { }
 
-static inline void plugin_insn_append(const void *from, size_t size)
+static inline void plugin_insn_append(abi_ptr pc, const void *from, size_t size)
 { }
 
 #endif /* CONFIG_PLUGIN */
diff --git a/include/qemu/plugin.h b/include/qemu/plugin.h
index b3172b147f..145f8a221a 100644
--- a/include/qemu/plugin.h
+++ b/include/qemu/plugin.h
@@ -163,10 +163,12 @@ struct qemu_plugin_tb {
 
 /**
  * qemu_plugin_tb_insn_get(): get next plugin record for translation.
- *
+ * @tb: the internal tb context
+ * @pc: address of instruction
  */
 static inline
-struct qemu_plugin_insn *qemu_plugin_tb_insn_get(struct qemu_plugin_tb *tb)
+struct qemu_plugin_insn *qemu_plugin_tb_insn_get(struct qemu_plugin_tb *tb,
+                                                 uint64_t pc)
 {
     struct qemu_plugin_insn *insn;
     int i, j;
@@ -179,6 +181,7 @@ struct qemu_plugin_insn *qemu_plugin_tb_insn_get(struct qemu_plugin_tb *tb)
     g_byte_array_set_size(insn->data, 0);
     insn->calls_helpers = false;
     insn->mem_helper = false;
+    insn->vaddr = pc;
 
     for (i = 0; i < PLUGIN_N_CB_TYPES; i++) {
         for (j = 0; j < PLUGIN_N_CB_SUBTYPES; j++) {