// Copyright 2019 the V8 project authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. #include <stdint.h> #include <limits> #include "src/base/build_config.h" #if !defined(UNDEFINED_SANITIZER) || !defined(V8_TARGET_ARCH_32_BIT) #error "This file is only needed for 32-bit UBSan builds." #endif // Compiling with -fsanitize=undefined on 32-bit platforms requires __mulodi4 // to be available. Usually it comes from libcompiler_rt, which our build // doesn't provide, so here is a custom implementation (inspired by digit_mul // in src/objects/bigint.cc). extern "C" int64_t __mulodi4(int64_t a, int64_t b, int* overflow) { // Multiply in 32-bit chunks. // For inputs [AH AL]*[BH BL], the result is: // // [AL*BL] // r_low // + [AL*BH] // r_mid1 // + [AH*BL] // r_mid2 // + [AH*BH] // r_high // = [R4 R3 R2 R1] // high = [R4 R3], low = [R2 R1] // // Where of course we must be careful with carries between the columns. uint64_t a_low = a & 0xFFFFFFFFu; uint64_t a_high = static_cast<uint64_t>(a) >> 32; uint64_t b_low = b & 0xFFFFFFFFu; uint64_t b_high = static_cast<uint64_t>(b) >> 32; uint64_t r_low = a_low * b_low; uint64_t r_mid1 = a_low * b_high; uint64_t r_mid2 = a_high * b_low; uint64_t r_high = a_high * b_high; uint64_t result1 = r_low + (r_mid1 << 32); if (result1 < r_low) r_high++; uint64_t result2 = result1 + (r_mid2 << 32); if (result2 < result1) r_high++; r_high += (r_mid1 >> 32) + (r_mid2 >> 32); int64_t result = static_cast<int64_t>(result2); uint64_t result_sign = (result >> 63); uint64_t expected_result_sign = (a >> 63) ^ (b >> 63); *overflow = (r_high > 0 || result_sign != expected_result_sign) ? 1 : 0; return result; }