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 "$" to make the end variable come after 20 // the data. Note that because of our technique the address of the start 21 // variable is actually the address of data that comes before our middle 22 // section. We also need to prevent the linker from adding any padding. Each 23 // technique we use for this is explained in the comments below. 24 //===----------------------------------------------------------------------===// 25 26 #include "sanitizer_platform.h" 27 #if SANITIZER_WINDOWS 28 #include <stdint.h> 29 30 extern "C" { 31 // Use uint64_t so the linker won't need to add any padding if it tries to word 32 // align the start of the 8-bit counters array. The array will always start 8 33 // bytes after __start_sancov_cntrs. 34 #pragma section(".SCOV$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