[PATCH] D74297: [ELF] Start a new PT_LOAD if LMA region is different

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: grimar, nickdesaulniers, peter.smith, ruiu, srhines.
Herald added subscribers: llvm-commits, arichardson, emaste.
Herald added a reviewer: espindola.
Herald added a project: LLVM.
MaskRay added a parent revision: D74286: [ELF] Respect output section alignment for AT> (non-null lmaRegion).

GNU ld has a counterintuitive lang_propagate_lma_regions rule.

  // .foo's LMA region is propagated to .bar because their VMA region is the same,
  // and .bar does not have an explicit output section address (addr_tree).
  .foo : { *(.foo) } >RAM AT> FLASH
  .bar : { *(.bar) } >RAM
  
  // An explicit output section address disables propagation.
  .foo : { *(.foo) } >RAM AT> FLASH
  .bar . : { *(.bar) } >RAM

In both cases, lld thinks .foo's LMA region is propagated and
places .bar in the same PT_LOAD, so lld diverges from GNU ld w.r.t. the
second case (lma-align.test).

This patch changes Writer<ELFT>::createPhdrs to disable propagation
(start a new PT_LOAD). A user of the first case can make linker scripts
portable by explicitly specifying `AT>`. By contrast, there was no
workaround for the old behavior.

This change uncovers another LMA related bug in assignOffsets() where
`ctx->lmaOffset = 0;` was omitted. It caused a spurious "load address
range overlaps" error for at2.test


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D74297

Files:
  lld/ELF/LinkerScript.cpp
  lld/ELF/Writer.cpp
  lld/test/ELF/linkerscript/Inputs/at2.s
  lld/test/ELF/linkerscript/at2.test
  lld/test/ELF/linkerscript/at8.test
  lld/test/ELF/linkerscript/lma-align.test

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