[all-commits] [llvm/llvm-project] 4f0ccc: [lld-macho][reland] Add basic symbol table output

[Jez Ng via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 4f0cccdd7a06ff60d3271638f47082b65f3793f1
      https://github.com/llvm/llvm-project/commit/4f0cccdd7a06ff60d3271638f47082b65f3793f1
  Author: Jez Ng <jezng at fb.com>
  Date:   2020-04-28 (Tue, 28 Apr 2020)

  Changed paths:
    M lld/MachO/SyntheticSections.cpp
    M lld/MachO/SyntheticSections.h
    M lld/MachO/Writer.cpp
    A lld/test/MachO/symtab.s

  Log Message:
  -----------
  [lld-macho][reland] Add basic symbol table output

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>

Originally committed in a3d95a50ee33 and reverted in fbae153ca583 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.

Differential Revision: https://reviews.llvm.org/D79050


  Commit: 62b8f32f7699807ec61c81e2ffceae584a7e6219
      https://github.com/llvm/llvm-project/commit/62b8f32f7699807ec61c81e2ffceae584a7e6219
  Author: Jez Ng <jezng at fb.com>
  Date:   2020-04-28 (Tue, 28 Apr 2020)

  Changed paths:
    M lld/MachO/Config.h
    M lld/MachO/Driver.cpp
    M lld/MachO/Options.td
    M lld/MachO/SyntheticSections.cpp
    M lld/MachO/SyntheticSections.h
    M lld/MachO/Writer.cpp
    R lld/test/MachO/Inputs/goodbye-dylib.yaml
    R lld/test/MachO/Inputs/hello-dylib.yaml
    A lld/test/MachO/Inputs/libgoodbye.s
    A lld/test/MachO/Inputs/libhello.s
    A lld/test/MachO/dylib.s
    M lld/test/MachO/dylink.s
    M lld/test/MachO/load-commands.s
    M lld/test/MachO/symtab.s

  Log Message:
  -----------
  [lld-macho][reland] Add support for emitting dylibs with a single symbol

This got reverted due to UBSAN errors in a diff lower in the stack,
which is being fixed in https://reviews.llvm.org/D79050. This diff is
otherwise identical to the original https://reviews.llvm.org/D76908
(which was committed in 9598778bd191 and reverted in b52bc2653bbc).

Differential Revision: https://reviews.llvm.org/D79051


Compare: https://github.com/llvm/llvm-project/compare/3421d1ede4c1...62b8f32f7699