Re: malloc() alignment on 32 bit

[Enrico Scholz <enrico.scholz@sigma-chemnitz.de>]

Sascha Hauer <sha@pengutronix.de> writes:

>> | zstd_decomp_init:536 workspace=8ff1a004+161320
>> | ERROR: initcall ubifs_init+0x1/0xc4 failed: Invalid argument
>> 
> If you had asked me which alignment we have then I would have said it's
> bigger. OTOH I never received any reports about insufficient alignment
> on ARM or any other 32bit architecture.

The code which failed for me was added 3 months ago

| commit b4a9782d4f56333e897dccc35c2c27e2605f6b93
| Author: Ahmad Fatoum <a.fatoum@pengutronix.de>
| Date:   Wed Jul 13 12:09:18 2022 +0200
| 
|     lib: zstd: sync with Linux

and the Kconfig options (FS_UBIFS_COMPRESSION_ZSTD) are set to "off"...


> I suspect we could just drop the check without any harm, but that's just
> a gut feeling because we never had any alignment issues.
>
> BTW are you sure ldrd/strd need 8 byte alignment?

Their EX variants (LDREXD + STREXD; see [1]).  Unaligned access on
plain LDRD/STRD is allowed on ARMv7-A.  But not on ARMv7-M or ARMv6 and
earlier.




Enrico

Footnotes:
[1]  https://developer.arm.com/documentation/ddi0406/c/Application-Level-Architecture/Application-Level-Memory-Model/Alignment-support/Unaligned-data-access