[PATCH] D66279: [ELF] Make LinkerScript::assignAddresses iterative

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: grimar, peter.smith, ruiu.
Herald added subscribers: llvm-commits, arichardson, emaste.
Herald added a reviewer: espindola.
Herald added a project: LLVM.

For the new test linkerscript/expr-converge.s, we currently set
st_value(a)=0xff00 and st_value(b)=0xff. PR42990

The following call tree demonstrates the problem:

  link<ELF64LE>(Args);
    Script->declareSymbols(); // insert a and b as absolute Defined
    Writer<ELFT>().run();
      Script->processSectionCommands();
        addSymbol(cmd);       // LinkerScript::getSymbolValue is used to retrieve values
      finalizeSections();
        forEachRelSec(scanRelocations<ELFT>);
          processRelocAux     // another problem PR42506, not affected by this patch
        finalizeAddressDependentContent(); // loop executed once
          script->assignAddresses(); // a = 0, b = 0xffff
      script->assignAddresses(); // a = 0xff00, _end = 0xffff

This patch

1. modifies assignAddress to track the original section/value of each symbol and return a symbol whose section/value has changed.
2. moves the post-finalizeSections assignAddress() inside the loop of finalizeAddressDependentContent() and makes it iterative. Symbol assignment may not converge so we make a few attempts before bailing out.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D66279

Files:
  ELF/LinkerScript.cpp
  ELF/LinkerScript.h
  ELF/Writer.cpp
  test/ELF/linkerscript/expr-converge.test

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