Re: [PATCH v3 6/8] crypto: x86/crc32c - Use idiomatic relative jump table

[Ard Biesheuvel]

On Mon, 14 Oct 2024 at 06:28, Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
>
> On Fri, Oct 11, 2024 at 07:08:54PM +0200, Ard Biesheuvel wrote:
> > diff --git a/arch/x86/crypto/crc32c-pcl-intel-asm_64.S b/arch/x86/crypto/crc32c-pcl-intel-asm_64.S
> > index bbcff1fb78cb..45b005935194 100644
> > --- a/arch/x86/crypto/crc32c-pcl-intel-asm_64.S
> > +++ b/arch/x86/crypto/crc32c-pcl-intel-asm_64.S
> > @@ -53,7 +53,7 @@
> >  .endm
> >
> >  .macro JMPTBL_ENTRY i
> > -.quad .Lcrc_\i
> > +.long .Lcrc_\i - jump_table
> >  .endm
> >
> >  .macro JNC_LESS_THAN j
> > @@ -169,7 +169,8 @@ SYM_FUNC_START(crc_pcl)
> >
> >       ## branch into array
> >       leaq    jump_table(%rip), %bufp
> > -     mov     (%bufp,%rax,8), %bufp
> > +     movslq  (%bufp,%rax,4), len
> > +     addq    len, %bufp
> >       JMP_NOSPEC bufp
>
> I think it would be much better to just get rid of the jump table here.
>

Good point.

> I have done this at
> https://lore.kernel.org/linux-crypto/20241014042447.50197-4-ebiggers@xxxxxxxxxx/
>

I'll go and take a look - thanks.