Re: Executable loading issues with erofs on arm?

[Gao Xiang <hsiangkao@linux.alibaba.com>]

Hi Jan,

On 2025/7/8 20:43, Jan Kiszka wrote:
> On 08.07.25 14:41, Jan Kiszka wrote:
>> Hi all,
>>
>> for some days, I'm trying to understand if we have an integration issue
>> with erofs or rather some upstream bug. After playing with various
>> parameters, it rather looks like the latter:
>>
>> $ ls -l erofs-dir/
>> total 132
>> -rwxr-xr-x 1 1000 users 132868 Jul  8 10:50 dash
>> (from Debian bookworm)
>> $ mkfs.erofs -z lz4hc erofs.img erofs-dir/
>> mkfs.erofs 1.8.6 (trixie version, but same happens with bookworm 1.5)
>> Build completed.
>> ------
>> Filesystem UUID: aae0b2f0-4ee4-4850-af49-3c1aad7fa30c
>> Filesystem total blocks: 17 (of 4096-byte blocks)
>> Filesystem total inodes: 2
>> Filesystem total metadata blocks: 1
>> Filesystem total deduplicated bytes (of source files): 0
>>
>> Now I have 6.15-rc5 and a defconfig-close setting for the 32-bit ARM
>> target BeagleBone Black. When booting into init=/bin/sh, then running
>>
>> # mount -t erofs /dev/mmcblk0p1 /mnt
>> erofs (device mmcblk0p1): mounted with root inode @ nid 36.
>> # /mnt/dash
>> Segmentation fault
>>
>> I once also got this:
>>
>> Alignment trap: not handling instruction 2b00 at [<004debc0>]
>> 8<--- cut here ---
>> Unhandled fault: alignment exception (0x001) at 0x000004d9
>> [000004d9] *pgd=00000000
>> Bus error
>>
>> All is fine if I
>>   - run the command once more
>>   - dump the file first (cat /mnt/dash > /dev/null; /mnt/dash)
> 
> Forgot to mention: That first dump when done via md5sum or so actually
> gives the right checksum. So pure reading of the binary is also ok, just
> trying to load it for execution fails on the first attempt.

Thanks for your report.  I rarely take care arm32 platform
because I don't have such setup.

but could you share a reproducible rootfs image and
I wonder if qemu could reproduce this?

Otherwise it's hard for me to debug this issue...

Thanks,
Gao Xiang

> 
> Jan
> 
>>   - boot a full Debian system and then mount & run the command
>>   - do not compress erofs
>>
>> Also broken is -z zstd, so the decompression algorithm itself should not
>> be the reason. I furthermore tested older kernels as well, namely
>> stable-derived 6.1-cip and 6.12-cip, and those are equally affected.
>>
>> Any ideas? I have CONFIG_EROFS_FS_DEBUG=y, but that does not trigger
>> anything. Is there anything I could instrument?
>>
>> Jan
>>
>