Re: [PATCH 0/9] tlsf: use 8-byte alignment for normal malloc allocations

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Enrico,

On 04.10.22 18:23, Enrico Scholz wrote:
> Ahmad Fatoum <a.fatoum@pengutronix.de> writes:
> 
>> TLSF currently uses only 4-byte alignment on 32-bit platforms, which isn't
>> enough for ldrd/strd on ARMv7. This series reworks TLSF a bit, so we always
>> have at least 8 byte alignment.  dlmalloc already has 8 byte alignment
>> minimum, so nothing to do there.
> 
> I am wondering whether alignment should be increased on 64 bit archs to
> 16 bytes as well.  ARMv8 spec [1] says
> 
> | exclusive pair access must be aligned to twice the data size, that is,
> | 128 bits for a pair of 64-bit values.
> 
> A github issue [2] mentions this alignment too.

Your quote is addressing exclusive pair access, which I think is something
a compiler would generate for lock-free __int128 access, not something that
we should encounter in barebox.

But yes, I believe we should have 16-byte alignment on 64-bit systems with
TLSF as we already do with dlmalloc, if only to be on the safe side.

This is unfortunately more complicated than what this PR does with 32-bit,
so I am leaving that as future exercise (or until we have a real world
example where this is required in barebox).

>> While this fixes real issues like what Enrico ran into, I'd suggest we only
>> this be taken into next only after v2022.10.0 is tagged,
> 
> This is ok for me; the issue disappeared with reverting the zstd patch.

Feel free to give it a test with the zstd patch reverted though. :)

Thanks,
Ahmad

> 
> 
> 
> Enrico
> 
> Footnotes:
> [1]  https://developer.arm.com/documentation/den0024/a/An-Introduction-to-the-ARMv8-Instruction-Sets/The-ARMv8-instruction-sets/Addressing
> 
> [2]  https://github.com/mattconte/tlsf/issues/16
> 


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