libsanitizer/sanitizer_common/sanitizer_coverage_win_sections.cc

   1 //===-- sanitizer_coverage_win_sections.cc --------------------------------===//
   2 //
   3 // This file is distributed under the University of Illinois Open Source
   4 // License. See LICENSE.TXT for details.
   5 //
   6 //===----------------------------------------------------------------------===//
   7 //
   8 // This file defines delimiters for Sanitizer Coverage's section. It contains
   9 // Windows specific tricks to coax the linker into giving us the start and stop
  10 // addresses of a section, as ELF linkers can do, to get the size of certain
  11 // arrays. According to https://msdn.microsoft.com/en-us/library/7977wcck.aspx
  12 // sections with the same name before "$" are sorted alphabetically by the
  13 // string that comes after "$" and merged into one section. We take advantage
  14 // of this by putting data we want the size of into the middle (M) of a section,
  15 // by using the letter "M" after "$". We get the start of this data (ie:
  16 // __start_section_name) by making the start variable come at the start of the
  17 // section (using the letter A after "$"). We do the same to get the end of the
  18 // data by using the letter "Z" after "$" to make the end variable come after
  19 // the data. Note that because of our technique the address of the start
  20 // variable is actually the address of data that comes before our middle
  21 // section. We also need to prevent the linker from adding any padding. Each
  22 // technique we use for this is explained in the comments below.
  23 //===----------------------------------------------------------------------===//
  24
  25 #include "sanitizer_platform.h"
  26 #if SANITIZER_WINDOWS
  27 #include <stdint.h>
  28 extern "C" {
  29 // The Guard array and counter array should both be merged into the .data
  30 // section to reduce the number of PE sections However, because PCTable is
  31 // constant it should be merged with the .rdata section.
  32 #pragma section(".SCOV$GA", read, write)  // NOLINT
  33 // Use align(1) to avoid adding any padding that will mess up clients trying to
  34 // determine the start and end of the array.
  35 __declspec(allocate(".SCOV$GA")) __declspec(align(1)) uint64_t
  36     __start___sancov_guards = 0;
  37 #pragma section(".SCOV$GZ", read, write)  // NOLINT
  38 __declspec(allocate(".SCOV$GZ")) __declspec(align(1)) uint64_t
  39     __stop___sancov_guards = 0;
  40
  41 #pragma section(".SCOV$CA", read, write)  // NOLINT
  42 __declspec(allocate(".SCOV$CA")) __declspec(align(1)) uint64_t
  43     __start___sancov_cntrs = 0;
  44 #pragma section(".SCOV$CZ", read, write)  // NOLINT
  45 __declspec(allocate(".SCOV$CZ")) __declspec(align(1)) uint64_t
  46     __stop___sancov_cntrs = 0;
  47
  48 #pragma comment(linker, "/MERGE:.SCOV=.data")
  49
  50 // Use uint64_t so there won't be any issues if the linker tries to word align
  51 // the pc array.
  52 #pragma section(".SCOVP$A", read)  // NOLINT
  53 __declspec(allocate(".SCOVP$A")) __declspec(align(1)) uint64_t
  54     __start___sancov_pcs = 0;
  55 #pragma section(".SCOVP$Z", read)  // NOLINT
  56 __declspec(allocate(".SCOVP$Z")) __declspec(align(1)) uint64_t
  57     __stop___sancov_pcs = 0;
  58
  59 #pragma comment(linker, "/MERGE:.SCOVP=.rdata")
  60 }
  61 #endif  // SANITIZER_WINDOWS