1// Copyright 2019 the V8 project authors. All rights reserved. 2// Use of this source code is governed by a BSD-style license that can be 3// found in the LICENSE file. 4 5#include <stdint.h> 6#include <limits> 7 8#include "src/base/build_config.h" 9 10#if !defined(UNDEFINED_SANITIZER) || !defined(V8_TARGET_ARCH_32_BIT) 11#error "This file is only needed for 32-bit UBSan builds." 12#endif 13 14// Compiling with -fsanitize=undefined on 32-bit platforms requires __mulodi4 15// to be available. Usually it comes from libcompiler_rt, which our build 16// doesn't provide, so here is a custom implementation (inspired by digit_mul 17// in src/objects/bigint.cc). 18extern "C" int64_t __mulodi4(int64_t a, int64_t b, int* overflow) { 19 // Multiply in 32-bit chunks. 20 // For inputs [AH AL]*[BH BL], the result is: 21 // 22 // [AL*BL] // r_low 23 // + [AL*BH] // r_mid1 24 // + [AH*BL] // r_mid2 25 // + [AH*BH] // r_high 26 // = [R4 R3 R2 R1] // high = [R4 R3], low = [R2 R1] 27 // 28 // Where of course we must be careful with carries between the columns. 29 uint64_t a_low = a & 0xFFFFFFFFu; 30 uint64_t a_high = static_cast<uint64_t>(a) >> 32; 31 uint64_t b_low = b & 0xFFFFFFFFu; 32 uint64_t b_high = static_cast<uint64_t>(b) >> 32; 33 34 uint64_t r_low = a_low * b_low; 35 uint64_t r_mid1 = a_low * b_high; 36 uint64_t r_mid2 = a_high * b_low; 37 uint64_t r_high = a_high * b_high; 38 39 uint64_t result1 = r_low + (r_mid1 << 32); 40 if (result1 < r_low) r_high++; 41 uint64_t result2 = result1 + (r_mid2 << 32); 42 if (result2 < result1) r_high++; 43 r_high += (r_mid1 >> 32) + (r_mid2 >> 32); 44 int64_t result = static_cast<int64_t>(result2); 45 uint64_t result_sign = (result >> 63); 46 uint64_t expected_result_sign = (a >> 63) ^ (b >> 63); 47 48 *overflow = (r_high > 0 || result_sign != expected_result_sign) ? 1 : 0; 49 return result; 50} 51