[RFC PATCH] target/s390x: move tcg_gen_insn_start to s390x_tr_insn_start

["Alex Bennée" <alex.bennee@linaro.org>]

We use INDEX_op_insn_start to make the start of instruction
boundaries. If we don't do it in the .insn_start hook things get
confused especially now plugins want to use that marking to identify
the start of instructions and will bomb out if it sees instrumented
ops before the first instruction boundary.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
 target/s390x/tcg/translate.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/target/s390x/tcg/translate.c b/target/s390x/tcg/translate.c
index f284870cd2..fe145ff2eb 100644
--- a/target/s390x/tcg/translate.c
+++ b/target/s390x/tcg/translate.c
@@ -6380,9 +6380,6 @@ static DisasJumpType translate_one(CPUS390XState *env, DisasContext *s)
     /* Search for the insn in the table.  */
     insn = extract_insn(env, s);
 
-    /* Emit insn_start now that we know the ILEN.  */
-    tcg_gen_insn_start(s->base.pc_next, s->cc_op, s->ilen);
-
     /* Not found means unimplemented/illegal opcode.  */
     if (insn == NULL) {
         qemu_log_mask(LOG_UNIMP, "unimplemented opcode 0x%02x%02x\n",
@@ -6550,8 +6547,30 @@ static void s390x_tr_tb_start(DisasContextBase *db, CPUState *cs)
 {
 }
 
+/*
+ * We just enough partial instruction decoding here to calculate the
+ * length of the instruction so we can drop the INDEX_op_insn_start
+ * before anything else is emitted in the TCGOp stream.
+ *
+ * See extract_insn for the full decode.
+ */
 static void s390x_tr_insn_start(DisasContextBase *dcbase, CPUState *cs)
 {
+    CPUS390XState *env = cs->env_ptr;
+    DisasContext *s = container_of(dcbase, DisasContext, base);
+    uint64_t insn, pc = s->base.pc_next;
+    int op, ilen;
+
+    if (unlikely(s->ex_value)) {
+        ilen = s->ex_value & 0xf;
+    } else {
+        insn = ld_code2(env, s, pc);  /* FIXME: don't reload same pc twice */
+        op = (insn >> 8) & 0xff;
+        ilen = get_ilen(op);
+    }
+
+    /* Emit insn_start now that we know the ILEN.  */
+    tcg_gen_insn_start(s->base.pc_next, s->cc_op, ilen);
 }
 
 static void s390x_tr_translate_insn(DisasContextBase *dcbase, CPUState *cs)
-- 
2.30.2