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