Identity transformation may corrupt file for some usecases

[last-g]

I wrote a simple script which applies identity transformation to test this lib. So the code is super simple and inspired by tests:

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RankNTypes #-}
module Main
  (
    main,
    strip_ghc_symbols,
  ) where


import qualified Data.ByteString as B
import qualified Data.ByteString.Lazy as L
import qualified Data.ElfEdit as EE
import qualified System.IO as IO

in_filename :: FilePath
in_filename = "./in.elf"

out_filename :: FilePath
out_filename = "./out.elf"


strip_ghc_symbols :: FilePath -> FilePath -> IO ()
strip_ghc_symbols in_path out_path =
  IO.withBinaryFile in_filename IO.ReadMode $ \in_h -> do
    bs <- B.hGetContents in_h
    withElf bs $ \e -> do

      let e_final = e
      -- write to output
      IO.withBinaryFile out_filename IO.WriteMode $ \out_h -> do
        B.hPut out_h $ L.toStrict (EE.renderElf e_final)


main :: IO ()
main = do
  putStrLn "hello, kitty"
  strip_ghc_symbols in_filename out_filename


--
withElf :: B.ByteString -> (forall w . EE.Elf w -> IO ()) -> IO ()
withElf bs f =
  case EE.parseElf bs of
    EE.Elf32Res err e32
      | null err  -> f e32
      | otherwise -> fail ("Failed to parse elf file: " ++ show err)
    EE.Elf64Res err e64
      | null err  -> f e64
      | otherwise -> fail ("Failed to parse elf file: " ++ show err)
    EE.ElfHeaderError _ e -> fail $ "Failed to parse elf file: " ++ show e

Unfortunately, the generated file doesn't look as correct as the original one.

lastg-mbp:fix-ghc-symbols lastg$ objdump -t in.elf > /dev/null
lastg-mbp:fix-ghc-symbols lastg$ echo $?
0
lastg-mbp:fix-ghc-symbols lastg$ objdump -t out.elf
/Applications/Xcode_9.3.0_fb.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/objdump: 'out.elf': Invalid data was encountered while parsing the file
lastg-mbp:fix-ghc-symbols lastg$ echo $?
1
lastg-mbp:fix-ghc-symbols lastg$ objdump -version
Apple LLVM version 9.1.0 (clang-902.0.39.1)
  Optimized build.
  Default target: x86_64-apple-darwin17.5.0
  Host CPU: skylake

  Registered Targets:
    aarch64    - AArch64 (little endian)
    aarch64_be - AArch64 (big endian)
    arm        - ARM
    arm64      - ARM64 (little endian)
    armeb      - ARM (big endian)
    thumb      - Thumb
    thumbeb    - Thumb (big endian)
    x86        - 32-bit X86: Pentium-Pro and above
    x86-64     - 64-bit X86: EM64T and AMD64

But in the same time out.elf seems to be valid for readelf and eu-readelf. And it's still runnable.

bins.zip

[joehendrix]

Do you any way of dumping more detailed error messages our from OSX' LLVM objdump?

I found one fix for .bss section alignment, but the symbol table differences do not affect readelf or GNU objdump?