The BLX immediate insn in the Thumb encoding always performs
a switch from Thumb to Arm state. This would be totally useless
in M-profile which has no Arm decoder, and so the instruction
does not exist at all there. Make the encoding UNDEF for M-profile.
(This part of the encoding space is used for the branch-future
and low-overhead-loop insns in v8.1M.)
Reviewed-by: Richard Henderson <richard.hender...@linaro.org>
Signed-off-by: Peter Maydell <peter.mayd...@linaro.org>
---
target/arm/translate.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/target/arm/translate.c b/target/arm/translate.c
index c145775438e..613bc0b9f1e 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -7880,6 +7880,14 @@ static bool trans_BLX_i(DisasContext *s, arg_BLX_i *a)
{
TCGv_i32 tmp;
+ /*
+ * BLX <imm> would be useless on M-profile; the encoding space
+ * is used for other insns from v8.1M onward, and UNDEFs before that.
+ */
+ if (arm_dc_feature(s, ARM_FEATURE_M)) {
+ return false;
+ }
+
/* For A32, ARM_FEATURE_V5 is checked near the start of the uncond block.
*/
if (s->thumb && (a->imm & 2)) {
return false;
--
2.20.1
