accel/tcg: Add insn_start to DisasContextBase

This is currently target-specific for many; begin making it
target independent.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

accel/tcg/translator.c

@@ -140,6 +140,7 @@ void translator_loop(CPUState *cpu, TranslationBlock *tb, int *max_insns,
     db->max_insns = *max_insns;
     db->singlestep_enabled = cflags & CF_SINGLE_STEP;
     db->saved_can_do_io = -1;
+    db->insn_start = NULL;
     db->host_addr[0] = host_pc;
     db->host_addr[1] = NULL;
 
@@ -157,6 +158,7 @@ void translator_loop(CPUState *cpu, TranslationBlock *tb, int *max_insns,
     while (true) {
         *max_insns = ++db->num_insns;
         ops->insn_start(db, cpu);
+        db->insn_start = tcg_last_op();
         tcg_debug_assert(db->is_jmp == DISAS_NEXT);  /* no early exit */
 
         if (plugin_enabled) {

include/exec/translator.h

@@ -74,6 +74,8 @@ typedef enum DisasJumpType {
  * @singlestep_enabled: "Hardware" single stepping enabled.
  * @saved_can_do_io: Known value of cpu->neg.can_do_io, or -1 for unknown.
  * @plugin_enabled: TCG plugin enabled in this TB.
+ * @insn_start: The last op emitted by the insn_start hook,
+ *              which is expected to be INDEX_op_insn_start.
  *
  * Architecture-agnostic disassembly context.
  */
@@ -87,6 +89,7 @@ typedef struct DisasContextBase {
     bool singlestep_enabled;
     int8_t saved_can_do_io;
     bool plugin_enabled;
+    struct TCGOp *insn_start;
     void *host_addr[2];
 } DisasContextBase;