[all-commits] [llvm/llvm-project] c49f83: [ELF] Don't advance sh_offset for an empty section...

[Fangrui Song via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: c49f83b6e9e383ac9df02ab4d95974d7bb1e5ddc
      https://github.com/llvm/llvm-project/commit/c49f83b6e9e383ac9df02ab4d95974d7bb1e5ddc
  Author: Fangrui Song <maskray at google.com>
  Date:   2020-05-04 (Mon, 04 May 2020)

  Changed paths:
    M lld/ELF/Writer.cpp
    M lld/test/ELF/linkerscript/at8.test
    M lld/test/ELF/linkerscript/empty-sections-expressions.test
    M lld/test/ELF/linkerscript/nobits-offset.s

  Log Message:
  -----------
  [ELF] Don't advance sh_offset for an empty section whose PT_LOAD is removed (due to p_memsz=0)

removeEmptyPTLoad() removes empty (p_memsz=0) PT_LOAD segments.  In
assignFileOffsets(), setFileOffset() unnecessarily advances file offsets
for containing empty sections.

This is exposed by arm Linux kernel's multi_v5_defconfig
(see https://bugs.llvm.org/show_bug.cgi?id=45632)

```
ld.lld (max-page-size=65536):
  [34] .init.data        PROGBITS        c0c24000 c34000 0128ac 00  WA  0   0 4096
  [35] .text_itcm        PROGBITS        fffe0000 c50000 000000 00  WA  0   0  1
  [36] .data_dtcm        PROGBITS        fffe8000 c58000 000000 00  WA  0   0  1
  [37] .data             PROGBITS        c0c38000 c58000 0647a0 00  WA  0   0 32

arm-linux-gnueabi-ld (max-page-size=65536):
  [23] .init.data        PROGBITS        c0c12000 c22000 0128ac 00  WA  0   0 4096
  [24] .text_itcm        PROGBITS        fffe0000 ca2558 000000 00   W  0   0  1
  [25] .data_dtcm        PROGBITS        fffe8000 ca2558 000000 00   W  0   0  1
  [26] .data             PROGBITS        c0c26000 c36000 0647a0 00  WA  0   0 32
```

This patch clears OutputSection::ptLoad if ptLoad is removed by
removeEmptyPTLoad(). Conceptually this removes "dangling" references.

Reviewed By: psmith

Differential Revision: https://reviews.llvm.org/D79254