diff options
Diffstat (limited to 'target')
| -rw-r--r-- | target/ppc/translate.c | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/target/ppc/translate.c b/target/ppc/translate.c index 576210d901..badc1ae1a3 100644 --- a/target/ppc/translate.c +++ b/target/ppc/translate.c @@ -3753,7 +3753,15 @@ static void gen_bcond(DisasContext *ctx, int type) * All ISAs up to v3 describe this form of bcctr as invalid but * some processors, ie. 64-bit server processors compliant with * arch 2.x, do implement a "test and decrement" logic instead, - * as described in their respective UMs. + * as described in their respective UMs. This logic involves CTR + * to act as both the branch target and a counter, which makes + * it basically useless and thus never used in real code. + * + * This form was hence chosen to trigger extra micro-architectural + * side-effect on real HW needed for the Spectre v2 workaround. + * It is up to guests that implement such workaround, ie. linux, to + * use this form in a way it just triggers the side-effect without + * doing anything else harmful. */ if (unlikely(!is_book3s_arch2x(ctx))) { gen_inval_exception(ctx, POWERPC_EXCP_INVAL_INVAL); |