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 
mergeInput(InputSection * input)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 
finalize()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 
writeTo(uint8_t * buf) const47 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.
mergeFlags(uint32_t inputFlags)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 }
75