lld/MachO/MergedOutputSection.cpp

   1 //===- OutputSection.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 #include "MergedOutputSection.h"
  10 #include "lld/Common/ErrorHandler.h"
  11 #include "lld/Common/Memory.h"
  12 #include "llvm/BinaryFormat/MachO.h"
  13
  14 using namespace llvm;
  15 using namespace llvm::MachO;
  16 using namespace lld;
  17 using namespace lld::macho;
  18
  19 void MergedOutputSection::mergeInput(InputSection *input) {
  20   if (inputs.empty()) {
  21     align = input->align;
  22     flags = input->flags;
  23   } else {
  24     mergeFlags(input->flags);
  25     align = std::max(align, input->align);
  26   }
  27
  28   inputs.push_back(input);
  29   input->parent = this;
  30 }
  31
  32 void MergedOutputSection::finalize() {
  33   uint64_t isecAddr = addr;
  34   uint64_t isecFileOff = fileOff;
  35   for (InputSection *isec : inputs) {
  36     isecAddr = alignTo(isecAddr, isec->align);
  37     isecFileOff = alignTo(isecFileOff, isec->align);
  38     isec->outSecOff = isecAddr - addr;
  39     isec->outSecFileOff = isecFileOff - fileOff;
  40     isecAddr += isec->getSize();
  41     isecFileOff += isec->getFileSize();
  42   }
  43   size = isecAddr - addr;
  44   fileSize = isecFileOff - fileOff;
  45 }
  46
  47 void MergedOutputSection::writeTo(uint8_t *buf) const {
  48   for (InputSection *isec : inputs) {
  49     isec->writeTo(buf + isec->outSecFileOff);
  50   }
  51 }
  52
  53 // TODO: this is most likely wrong; reconsider how section flags
  54 // are actually merged. The logic presented here was written without
  55 // any form of informed research.
  56 void MergedOutputSection::mergeFlags(uint32_t inputFlags) {
  57   uint8_t sectionFlag = MachO::SECTION_TYPE & inputFlags;
  58   if (sectionFlag != (MachO::SECTION_TYPE & flags))
  59     error("Cannot add merge section; inconsistent type flags " +
  60           Twine(sectionFlag));
  61
  62   uint32_t inconsistentFlags =
  63       MachO::S_ATTR_DEBUG | MachO::S_ATTR_STRIP_STATIC_SYMS |
  64       MachO::S_ATTR_NO_DEAD_STRIP | MachO::S_ATTR_LIVE_SUPPORT;
  65   if ((inputFlags ^ flags) & inconsistentFlags)
  66     error("Cannot add merge section; cannot merge inconsistent flags");
  67
  68   // Negate pure instruction presence if any section isn't pure.
  69   uint32_t pureMask = ~MachO::S_ATTR_PURE_INSTRUCTIONS | (inputFlags & flags);
  70
  71   // Merge the rest
  72   flags |= inputFlags;
  73   flags &= pureMask;
  74 }