From e0a0c8322b8ebcdad674f443a3e86db8708d6738 Mon Sep 17 00:00:00 2001 From: Richard Henderson Date: Wed, 28 Aug 2019 18:32:58 -0700 Subject: [PATCH] target/arm: Fix SMMLS argument order The previous simplification got the order of operands to the subtraction wrong. Since the 64-bit product is the subtrahend, we must use a 64-bit subtract to properly compute the borrow from the low-part of the product. Fixes: 5f8cd06ebcf5 ("target/arm: Simplify SMMLA, SMMLAR, SMMLS, SMMLSR") Reported-by: Laurent Desnogues Signed-off-by: Richard Henderson Tested-by: Laurent Desnogues Message-id: 20190829013258.16102-1-richard.henderson@linaro.org Reviewed-by: Peter Maydell Signed-off-by: Peter Maydell --- target/arm/translate.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/target/arm/translate.c b/target/arm/translate.c index 78d93f63ca..cfebd35d26 100644 --- a/target/arm/translate.c +++ b/target/arm/translate.c @@ -8831,7 +8831,16 @@ static void disas_arm_insn(DisasContext *s, unsigned int insn) if (rd != 15) { tmp3 = load_reg(s, rd); if (insn & (1 << 6)) { - tcg_gen_sub_i32(tmp, tmp, tmp3); + /* + * For SMMLS, we need a 64-bit subtract. + * Borrow caused by a non-zero multiplicand + * lowpart, and the correct result lowpart + * for rounding. + */ + TCGv_i32 zero = tcg_const_i32(0); + tcg_gen_sub2_i32(tmp2, tmp, zero, tmp3, + tmp2, tmp); + tcg_temp_free_i32(zero); } else { tcg_gen_add_i32(tmp, tmp, tmp3); } @@ -10075,7 +10084,14 @@ static void disas_thumb2_insn(DisasContext *s, uint32_t insn) if (insn & (1 << 20)) { tcg_gen_add_i32(tmp, tmp, tmp3); } else { - tcg_gen_sub_i32(tmp, tmp, tmp3); + /* + * For SMMLS, we need a 64-bit subtract. + * Borrow caused by a non-zero multiplicand lowpart, + * and the correct result lowpart for rounding. + */ + TCGv_i32 zero = tcg_const_i32(0); + tcg_gen_sub2_i32(tmp2, tmp, zero, tmp3, tmp2, tmp); + tcg_temp_free_i32(zero); } tcg_temp_free_i32(tmp3); }