Messages in this thread | | | From | Nick Desaulniers <> | Date | Mon, 9 Nov 2020 13:09:31 -0800 | Subject | Re: [PATCH] ARM: decompressor: avoid ADRL pseudo-instruction |
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On Mon, Nov 9, 2020 at 12:53 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > On Mon, 9 Nov 2020 at 21:52, Nick Desaulniers <ndesaulniers@google.com> 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@kernel.org> > > Suggested-by: Jian Cai <jiancai@google.com> > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > > --- > > 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@kernel.org/
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
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