Re: [PATCH] ARM: decompressor: avoid ADRL pseudo-instruction

[Nick Desaulniers]

On Mon, Nov 9, 2020 at 12:53 PM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
>
> On Mon, 9 Nov 2020 at 21:52, Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote:
> >
> > As Ard notes in
> > commit 54781938ec34 ("crypto: arm/sha256-neon - avoid ADRL pseudo
> > instruction")
> > commit 0f5e8323777b ("crypto: arm/sha512-neon - avoid ADRL pseudo
> > instruction")
> >
> >   The ADRL pseudo instruction is not an architectural construct, but a
> >   convenience macro that was supported by the ARM proprietary assembler
> >   and adopted by binutils GAS as well, but only when assembling in 32-bit
> >   ARM mode. Therefore, it can only be used in assembler code that is known
> >   to assemble in ARM mode only, but as it turns out, the Clang assembler
> >   does not implement ADRL at all, and so it is better to get rid of it
> >   entirely.
> >
> >   So replace the ADRL instruction with a ADR instruction that refers to
> >   a nearer symbol, and apply the delta explicitly using an additional
> >   instruction.
> >
> > We can use the same technique to generate the same offset. It looks like
> > the ADRL pseudo instruction assembles to two SUB instructions in this
> > case. Because the largest immediate operand that can be specified for
> > this instruction is 0x400, and the distance between the reference and
> > the symbol are larger than that, we need to use an intermediary symbol
> > (cache_off in this case) to calculate the full range.
> >
> > Suggested-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> > Suggested-by: Jian Cai <jiancai@xxxxxxxxxx>
> > Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> > ---
> >  arch/arm/boot/compressed/head.S | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> > index 2e04ec5b5446..b3eac6f9a709 100644
> > --- a/arch/arm/boot/compressed/head.S
> > +++ b/arch/arm/boot/compressed/head.S
> > @@ -1440,7 +1440,9 @@ ENTRY(efi_enter_kernel)
> >                 mov     r4, r0                  @ preserve image base
> >                 mov     r8, r1                  @ preserve DT pointer
> >
> > - ARM(          adrl    r0, call_cache_fn       )
> > + ARM(          sub     r0, pc, #.L__efi_enter_kernel-cache_off )
> > + ARM(          sub     r0, r0, #cache_off-call_cache_fn        )
> > +.L__efi_enter_kernel:
> >   THUMB(                adr     r0, call_cache_fn       )
> >                 adr     r1, 0f                  @ clean the region of code we
> >                 bl      cache_clean_flush       @ may run with the MMU off
> > --
> > 2.29.2.222.g5d2a92d10f8-goog
> >
>
> This is already fixed in Russell's for-next tree.

Ah right, trolling through lore, there was:
https://lore.kernel.org/linux-arm-kernel/20200914095706.3985-1-ardb@xxxxxxxxxx/

I didn't see anything in linux-next today, or
https://www.armlinux.org.uk/developer/patches/ Incoming or Applied.

Did it just get merged into the for-next branch, or is for-next not
getting pulled into linux-next?
-- 
Thanks,
~Nick Desaulniers