68 lines · cpp
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-exception6//7//===----------------------------------------------------------------------===//8//9// This file defines delimiters for Sanitizer Coverage's section. It contains10// Windows specific tricks to coax the linker into giving us the start and stop11// addresses of a section, as ELF linkers can do, to get the size of certain12// arrays. According to https://msdn.microsoft.com/en-us/library/7977wcck.aspx13// sections with the same name before "$" are sorted alphabetically by the14// string that comes after "$" and merged into one section. We take advantage15// of this by putting data we want the size of into the middle (M) of a section,16// by using the letter "M" after "$". We get the start of this data (ie:17// __start_section_name) by making the start variable come at the start of the18// section (using the letter A after "$"). We do the same to get the end of the19// data by using the letter "Z" after "$" to make the end variable come after20// the data. Note that because of our technique the address of the start21// variable is actually the address of data that comes before our middle22// section. We also need to prevent the linker from adding any padding. Each23// technique we use for this is explained in the comments below.24//===----------------------------------------------------------------------===//25 26#include "sanitizer_platform.h"27#if SANITIZER_WINDOWS28#include <stdint.h>29 30extern "C" {31// Use uint64_t so the linker won't need to add any padding if it tries to word32// align the start of the 8-bit counters array. The array will always start 833// bytes after __start_sancov_cntrs.34#pragma section(".SCOV$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, containing39// it. This can cause a mismatch between the number of PCs and counters since40// each PCTable element is 8 bytes (unlike counters which are 1 byte) so no41// padding would be added to align .SCOVP$Z, However, if .SCOV$CZ section is 142// byte, the linker won't try to align it on an 8-byte boundary, so use a43// uint8_t for __stop_sancov_cntrs.44#pragma section(".SCOV$CZ", read, write)45__declspec(allocate(".SCOV$CZ")) __declspec(align(1)) uint8_t46 __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_t52 __stop___sancov_guards = 0;53 54// The guard array and counter array should both be merged into the .data55// section to reduce the number of PE sections. However, because PCTable is56// 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_t63 __stop___sancov_pcs = 0;64 65#pragma comment(linker, "/MERGE:.SCOVP=.rdata")66}67#endif // SANITIZER_WINDOWS68