sanitizer_coverage_win_sections.cpp revision 360784
1//===-- sanitizer_coverage_win_sections.cpp -------------------------------===// 2// 3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4// See https://llvm.org/LICENSE.txt for license information. 5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6// 7//===----------------------------------------------------------------------===// 8// 9// This file defines delimiters for Sanitizer Coverage's section. It contains 10// Windows specific tricks to coax the linker into giving us the start and stop 11// addresses of a section, as ELF linkers can do, to get the size of certain 12// arrays. According to https://msdn.microsoft.com/en-us/library/7977wcck.aspx 13// sections with the same name before "$" are sorted alphabetically by the 14// string that comes after "$" and merged into one section. We take advantage 15// of this by putting data we want the size of into the middle (M) of a section, 16// by using the letter "M" after "$". We get the start of this data (ie: 17// __start_section_name) by making the start variable come at the start of the 18// section (using the letter A after "$"). We do the same to get the end of the 19// data by using the letter "Z" after "$" to make the end variable come after 20// the data. Note that because of our technique the address of the start 21// variable is actually the address of data that comes before our middle 22// section. We also need to prevent the linker from adding any padding. Each 23// technique we use for this is explained in the comments below. 24//===----------------------------------------------------------------------===// 25 26#include "sanitizer_platform.h" 27#if SANITIZER_WINDOWS 28#include <stdint.h> 29 30extern "C" { 31// Use uint64_t so the linker won't need to add any padding if it tries to word 32// align the start of the 8-bit counters array. The array will always start 8 33// bytes after __start_sancov_cntrs. 34#pragma section(".SCOV$CA", read, write) 35__declspec(allocate(".SCOV$CA")) uint64_t __start___sancov_cntrs = 0; 36 37// Even though we said not to align __stop__sancov_cntrs (using the "align" 38// declspec), MSVC's linker may try to align the section, .SCOV$CZ, containing 39// it. This can cause a mismatch between the number of PCs and counters since 40// each PCTable element is 8 bytes (unlike counters which are 1 byte) so no 41// padding would be added to align .SCOVP$Z, However, if .SCOV$CZ section is 1 42// byte, the linker won't try to align it on an 8-byte boundary, so use a 43// uint8_t for __stop_sancov_cntrs. 44#pragma section(".SCOV$CZ", read, write) 45__declspec(allocate(".SCOV$CZ")) __declspec(align(1)) uint8_t 46 __stop___sancov_cntrs = 0; 47 48#pragma section(".SCOV$GA", read, write) 49__declspec(allocate(".SCOV$GA")) uint64_t __start___sancov_guards = 0; 50#pragma section(".SCOV$GZ", read, write) 51__declspec(allocate(".SCOV$GZ")) __declspec(align(1)) uint8_t 52 __stop___sancov_guards = 0; 53 54// The guard array and counter array should both be merged into the .data 55// section to reduce the number of PE sections. However, because PCTable is 56// constant it should be merged with the .rdata section. 57#pragma comment(linker, "/MERGE:.SCOV=.data") 58 59#pragma section(".SCOVP$A", read) 60__declspec(allocate(".SCOVP$A")) uint64_t __start___sancov_pcs = 0; 61#pragma section(".SCOVP$Z", read) 62__declspec(allocate(".SCOVP$Z")) __declspec(align(1)) uint8_t 63 __stop___sancov_pcs = 0; 64 65#pragma comment(linker, "/MERGE:.SCOVP=.rdata") 66} 67#endif // SANITIZER_WINDOWS 68