| Issue |
108946
|
| Summary |
llvm-objcopy does not seem to handle `-O binary` correctly, adds PE header to the output
|
| Labels |
tools:llvm-objcopy/strip
|
| Assignees |
|
| Reporter |
mgorny
|
In Gentoo, we're using `objcopy` to extract the Linux kernel image from UKI image.
Reproducer:
```
wget https://distfiles.gentoo.org/distfiles/1d/gentoo-kernel-6.10.9-1.amd64.gpkg.tar
tar -xf gentoo-kernel-6.10.9-1.amd64.gpkg.tar gentoo-kernel-6.10.9-1/image.tar.xz
tar -xf gentoo-kernel-6.10.9-1/image.tar.xz image/usr/src/linux-6.10.9-gentoo-dist/arch/x86/boot/uki.efi
objcopy -O binary -j.linux image/usr/src/linux-6.10.9-gentoo-dist/arch/x86/boot/uki.efi bzImage
```
Comparing the files created by GNU objcopy and LLVM objcopy:
```
-rwxr-xr-x 1 mgorny mgorny 19606512 09-17 11:15 bzImage.gnu
-rwxr-xr-x 1 mgorny mgorny 19607040 09-17 11:15 bzImage.llvm
```
The LLVM file has additional 512 bytes at the front:
```
00000000 4d 5a 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |MZ..............|
00000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00000030 00 00 00 00 00 00 00 00 00 00 00 00 40 00 00 00 |............@...|
00000040 50 45 00 00 64 86 01 00 de 9a d0 66 00 00 00 00 |PE..d......f....|
00000050 00 00 00 00 f0 00 2e 02 0b 02 00 00 ae 87 00 00 |................|
00000060 00 00 00 00 00 00 00 00 e0 96 00 00 00 10 00 00 |................|
00000070 00 00 f9 4d 01 00 00 00 00 10 00 00 00 02 00 00 |...M............|
00000080 00 00 00 00 00 01 05 00 01 00 01 00 00 00 00 00 |................|
00000090 00 c0 dd 05 00 02 00 00 00 00 00 00 0a 00 60 01 |..............`.|
000000a0 00 00 10 00 00 00 00 00 00 10 00 00 00 00 00 00 |................|
*
000000c0 00 00 00 00 10 00 00 00 00 00 00 00 00 00 00 00 |................|
000000d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000000e0 00 00 00 00 00 00 00 00 00 28 dd 05 f0 09 00 00 |.........(......|
000000f0 00 10 01 00 84 00 00 00 00 00 00 00 00 00 00 00 |................|
00000100 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00000140 00 00 00 00 00 00 00 00 2e 6c 69 6e 75 78 00 00 |.........linux..|
00000150 f0 2b 2b 01 00 90 b2 04 00 2c 2b 01 00 02 00 00 |.++......,+.....|
00000160 00 00 00 00 00 00 00 00 00 00 00 00 20 00 00 40 |............ ..@|
00000170 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
```
And 16 bytes (of padding?) at the end:
```
012b2df0 cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc |................|
```
In fact, if I run GNU objcopy without `-O binary`, I get roughly the same format as LLVM gives. This leads me to conclude that LLVM objcopy does not implement `-O binary` correctly, and instead uses PE output, same as the original file.
```
$ file bzImage.*
bzImage.gnu: Linux kernel x86 boot executable bzImage, version 6.10.9-gentoo-dist (root@devbox) #1 SMP PREEMPT_DYNAMIC Sun Sep 8 11:45:05 -00 2024, RO-rootFS, swap_dev 0X12, Normal VGA
bzImage.gnu-without-O-binary: PE32+ executable (EFI application) x86-64 (stripped to external PDB), for MS Windows
bzImage.llvm: PE32+ executable (EFI application) x86-64 (stripped to external PDB), for MS Windows
```
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