Re: [PATCH v5] eal: fix unaligned loads/stores in rte_memcpy_generic

[Thomas Monjalon <thomas@monjalon.net>]

04/02/2022 18:16, Ananyev, Konstantin:
> 
> > Calls to rte_memcpy_generic could result in unaligned loads/stores for
> > 1 < n < 16. This is undefined behavior according to the C standard,
> > and it gets flagged by the clang undefined behavior sanitizer.
> > 
> > rte_memcpy_generic is called with unaligned src and dst addresses.
> > When 1 < n < 16, the code would cast both src and dst to a qword,
> > dword or word pointer, without verifying the alignment of src/dst. The
> > code was changed to use a packed structure to perform the unaligned
> > load/store operations. This results in unaligned load/store operations
> > to be C standards-compliant.
> 
> Still not sure we need to fix that:
> This is x86 specific code-path, and as I remember on x86 there are no
> penalties for unaligned access to 2/4/8 byte values. 
> Though I like introduction of rte_mov15_or_less() function -t helps
> with code dedup. 

Any more opinions?