[PATCH] D71035: [llvm-objcopy][ELF] -O binary: use LMA instead of sh_offset to decide where to write section contents

[James Henderson via Phabricator via llvm-commits]

jhenderson added a comment.

I've been playing around with the YAML from the test to experiment with other situations using GNU objcopy, and I'm not convinced that your statement about the algorithm is quite accurate, and indeed I see behaviour differences between GNU objcopy and llvm-objcopy with this patch. Unfortunately, I haven't been able to figure out what the actual algorithm is, so it's possible I'm just misunderstanding something. Here is an example I used:

Input:

  --- !ELF
  FileHeader:
    Class:           ELFCLASS64
    Data:            ELFDATA2LSB
    Type:            ET_EXEC
    Machine:         EM_X86_64
  Sections:
    - Name:            .text
      Type:            SHT_PROGBITS
      Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
      Address:         0x1000
      AddressAlign:    0x0000000000001000
      Content:         "c3c3c3c3"
    - Name:            .data
      Type:            SHT_PROGBITS
      Flags:           [ SHF_ALLOC ]
      Address:         0x3000
      AddressAlign:    0x0000000000001000
      Content:         "3232"
    - Name: .baz
      Type: SHT_PROGBITS
      Size: 0x2000
  ProgramHeaders:
    - Type: PT_LOAD
      Flags: [ PF_R, PF_W ]
      VAddr: 0x2000
      PAddr: 0x4000
      FileSize: 0x1800
      MemSize: 0x1800
      Sections:
        - Section: .data

GNU objcopy output:

  000000 c3c3 c3c3 0000 0000 0000 0000 0000 0000
  000010 0000 0000 0000 0000 0000 0000 0000 0000
  *
  003000 3232
  003002

llvm-objcopy output:

  000000 c3c3 c3c3 0000 0000 0000 0000 0000 0000
  000010 0000 0000 0000 0000 0000 0000 0000 0000
  *
  004000 3232
  004002

I also noticed several differences that may be unrelated to this issue when sections are not in segments. Speaking of which, did you mean for this to be the case for .text in this test?


Repository:
  rG LLVM Github Monorepo

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