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

source code of compiler-rt/lib/sanitizer_common/sanitizer_coverage_win_sections.cpp