On 6/2/20 11:43 PM, Philippe Mathieu-Daudé wrote: > > Hi Catherine, > > On 6/3/20 7:23 AM, [email protected] wrote: >> From: "Catherine A. Frederick" <[email protected]> >> >> Signed-off-by: "Catherine A. Frederick" <[email protected]> >> --- >> tcg/ppc/tcg-target.inc.c | 4 ++++ >> 1 file changed, 4 insertions(+) >> >> diff --git a/tcg/ppc/tcg-target.inc.c b/tcg/ppc/tcg-target.inc.c >> index ee1f9227c1..a5450a5e67 100644 >> --- a/tcg/ppc/tcg-target.inc.c >> +++ b/tcg/ppc/tcg-target.inc.c >> @@ -790,21 +790,25 @@ static inline void tcg_out_ext32u(TCGContext *s, >> TCGReg dst, TCGReg src) >> >> static inline void tcg_out_shli32(TCGContext *s, TCGReg dst, TCGReg src, >> int c) >> { >> + c = ((unsigned)c > 32) ? 32 : c; >> tcg_out_rlw(s, RLWINM, dst, src, c, 0, 31 - c); >> } >> >> static inline void tcg_out_shli64(TCGContext *s, TCGReg dst, TCGReg src, >> int c) >> { >> + c = ((unsigned)c > 64) ? 64 : c; >> tcg_out_rld(s, RLDICR, dst, src, c, 63 - c); >> } >> >> static inline void tcg_out_shri32(TCGContext *s, TCGReg dst, TCGReg src, >> int c) >> { >> + c = ((unsigned)c > 32) ? 32 : c; >> tcg_out_rlw(s, RLWINM, dst, src, 32 - c, c, 31); >> } >> >> static inline void tcg_out_shri64(TCGContext *s, TCGReg dst, TCGReg src, >> int c) >> { >> + c = ((unsigned)c > 64) ? 64 : c; >> tcg_out_rld(s, RLDICL, dst, src, 64 - c, c); >> } > > I agree there is a bug, but I am not sure we should silently cap the > value this way. I'd rather see the caller provide a value in range, and > maybe the callee use 'tcg_debug_assert(c <= RANGE);' to catch future new > caller added missing the range check.
We have done this before: see 1fd95946657. In tcg/README, we note that out-of-range shifts produce undefined results, but should not trap with illegal instruction. I would like to know more about where these out-of-range shifts are being generated, but I do know that there are innocent ways by which this can happen. For instance, one way in which we can translate a guest in which out-of-range shifts produce zero is x = (shift < 32 ? y << shift : 0) using INDEX_op_movcond_i32 for the ?: operator. Which means that we use the original (out-of-range) shift and subsequently discard the undefined result. Catherine, I think it would be more appropriate to mask C rather than bound it to another out-of-range value: c &= 31 or c &= 64, with a comment about avoiding an illegal instruction, just as in the tcg/sparc patch I reference above. r~
