[PATCH] D79050: [lld-macho][reland] Add basic symbol table output

[Jez Ng via Phabricator via llvm-commits]

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int3 updated this revision to Diff 260789.
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int3 added a child revision: D79051: [lld-macho][reland] Add support for emitting dylibs with a single symbol.

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This diff implements basic support for writing a symbol table.

Attributes are loosely supported for extern symbols and not at all for
other types.

Initial version by Kellie Medlin <kelliem at fb.com>

Original diff got reverted due to UBSAN erroring over unaligned writes.
That has been fixed in the current diff with the following changes:

  diff --git a/lld/MachO/SyntheticSections.cpp b/lld/MachO/SyntheticSections.cpp
  --- a/lld/MachO/SyntheticSections.cpp
  +++ b/lld/MachO/SyntheticSections.cpp
  @@ -133,6 +133,9 @@ SymtabSection::SymtabSection(StringTableSection &stringTableSection)
       : stringTableSection(stringTableSection) {
     segname = segment_names::linkEdit;
     name = section_names::symbolTable;
  +  // TODO: When we introduce the SyntheticSections superclass, we should make
  +  // all synthetic sections aligned to WordSize by default.
  +  align = WordSize;
   }
  
   size_t SymtabSection::getSize() const {
  diff --git a/lld/MachO/Writer.cpp b/lld/MachO/Writer.cpp
  --- a/lld/MachO/Writer.cpp
  +++ b/lld/MachO/Writer.cpp
  @@ -371,6 +371,7 @@ void Writer::assignAddresses(OutputSegment *seg) {
       ArrayRef<InputSection *> sections = p.second;
       for (InputSection *isec : sections) {
         addr = alignTo(addr, isec->align);
  +      // We must align the file offsets too to avoid misaligned writes of
  +      // structs.
  +      fileOff = alignTo(fileOff, isec->align);
         isec->addr = addr;
         addr += isec->getSize();
         fileOff += isec->getFileSize();
  @@ -396,6 +397,7 @@ void Writer::writeSections() {
       uint64_t fileOff = seg->fileOff;
       for (auto &sect : seg->getSections()) {
         for (InputSection *isec : sect.second) {
  +        fileOff = alignTo(fileOff, isec->align);
           isec->writeTo(buf + fileOff);
           fileOff += isec->getFileSize();
         }

I don't think it's easy to write a test for alignment (that doesn't
involve brittly hard-coding file offsets), so there isn't one... but
UBSAN builds pass now.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D79050

Files:
  lld/MachO/SyntheticSections.cpp
  lld/MachO/SyntheticSections.h
  lld/MachO/Writer.cpp
  lld/test/MachO/symtab.s

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