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Fri, 26 Apr 2024 07:49:00 +0000 Received: from AS8P193MB1285.EURP193.PROD.OUTLOOK.COM ([fe80::e65d:5dd2:5662:c61f]) by AS8P193MB1285.EURP193.PROD.OUTLOOK.COM ([fe80::e65d:5dd2:5662:c61f%4]) with mapi id 15.20.7472.045; Fri, 26 Apr 2024 07:49:00 +0000 Message-ID: Date: Fri, 26 Apr 2024 09:50:58 +0200 User-Agent: Mozilla Thunderbird Content-Language: en-US To: "gdb-patches@sourceware.org" From: Bernd Edlinger Subject: [PATCH] sim: riscv: Fix undefined behaviour in mulh and similar X-TMN: [CfgC9azgdAhzVtrEDfVFigmeb3w72waKTz6ElNMkKeVWBPyxS3GC/6co5KFG73XP] X-ClientProxiedBy: FR5P281CA0045.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:f3::12) To AS8P193MB1285.EURP193.PROD.OUTLOOK.COM (2603:10a6:20b:333::21) X-Microsoft-Original-Message-ID: <3be04323-d436-40f1-b139-325e5cf57ef3@hotmail.de> MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: AS8P193MB1285:EE_|DU2P193MB2369:EE_ X-MS-Office365-Filtering-Correlation-Id: 921fb969-c20a-4c5c-9e31-08dc65c555e7 X-Microsoft-Antispam: BCL:0; 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Also the __int128 multiplication in mulhu can overflow, and must be done with unsigned __int128 to be safe. And of course, the sign change in mulhsu can overflow too. And also in execute_m there are a couple of possibly overflowing multiplications in MULW, MULH and MULHSU. The latter is probably harmless, because the signed * unsigned type multiplication is done in unsigned, but it is at least clearer what is intended, this way. --- sim/riscv/sim-main.c | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-) diff --git a/sim/riscv/sim-main.c b/sim/riscv/sim-main.c index f6f6e2384e8..1815d7f2a6c 100644 --- a/sim/riscv/sim-main.c +++ b/sim/riscv/sim-main.c @@ -651,7 +651,7 @@ static uint64_t mulhu (uint64_t a, uint64_t b) { #ifdef HAVE___INT128 - return ((__int128)a * b) >> 64; + return ((unsigned __int128)a * b) >> 64; #else uint64_t t; uint32_t y1, y2, y3; @@ -677,16 +677,16 @@ static uint64_t mulh (int64_t a, int64_t b) { int negate = (a < 0) != (b < 0); - uint64_t res = mulhu (a < 0 ? -a : a, b < 0 ? -b : b); - return negate ? ~res + (a * b == 0) : res; + uint64_t res = mulhu (a < 0 ? -(uint64_t)a : a, b < 0 ? -(uint64_t)b : b); + return negate ? ~res + ((uint64_t)a * (uint64_t)b == 0) : res; } static uint64_t mulhsu (int64_t a, uint64_t b) { int negate = a < 0; - uint64_t res = mulhu (a < 0 ? -a : a, b); - return negate ? ~res + (a * b == 0) : res; + uint64_t res = mulhu (a < 0 ? -(uint64_t)a : a, b); + return negate ? ~res + ((uint64_t)a * b == 0) : res; } static sim_cia @@ -757,16 +757,16 @@ execute_m (SIM_CPU *cpu, unsigned_word iw, const struct riscv_opcode *op) TRACE_INSN (cpu, "mulw %s, %s, %s; // %s = %s * %s", rd_name, rs1_name, rs2_name, rd_name, rs1_name, rs2_name); RISCV_ASSERT_RV64 (cpu, "insn: %s", op->name); - store_rd (cpu, rd, EXTEND32 ((int32_t) riscv_cpu->regs[rs1] - * (int32_t) riscv_cpu->regs[rs2])); + store_rd (cpu, rd, EXTEND32 ((uint32_t) riscv_cpu->regs[rs1] + * (uint32_t) riscv_cpu->regs[rs2])); break; case MATCH_MULH: TRACE_INSN (cpu, "mulh %s, %s, %s; // %s = %s * %s", rd_name, rs1_name, rs2_name, rd_name, rs1_name, rs2_name); if (RISCV_XLEN (cpu) == 32) store_rd (cpu, rd, - ((int64_t)(signed_word) riscv_cpu->regs[rs1] - * (int64_t)(signed_word) riscv_cpu->regs[rs2]) >> 32); + ((uint64_t)(signed_word) riscv_cpu->regs[rs1] + * (uint64_t)(signed_word) riscv_cpu->regs[rs2]) >> 32); else store_rd (cpu, rd, mulh (riscv_cpu->regs[rs1], riscv_cpu->regs[rs2])); break; @@ -783,7 +783,7 @@ execute_m (SIM_CPU *cpu, unsigned_word iw, const struct riscv_opcode *op) TRACE_INSN (cpu, "mulhsu %s, %s, %s; // %s = %s * %s", rd_name, rs1_name, rs2_name, rd_name, rs1_name, rs2_name); if (RISCV_XLEN (cpu) == 32) - store_rd (cpu, rd, ((int64_t)(signed_word) riscv_cpu->regs[rs1] + store_rd (cpu, rd, ((uint64_t)(signed_word) riscv_cpu->regs[rs1] * (uint64_t)riscv_cpu->regs[rs2]) >> 32); else store_rd (cpu, rd, mulhsu (riscv_cpu->regs[rs1], riscv_cpu->regs[rs2]));