Re: [PATCH 1/3] arm64: vdso32: drop the test for dmb ishld

On Wed, Oct 13, 2021 at 1:46 AM Nick Desaulniers
[off-list ref] wrote:

Binutils added support for this instruction in commit
e797f7e0b2bedc9328d4a9a0ebc63ca7a2dbbebc which shipped in 2.34 (just
missing the 2.33 release) but was cherry-picked into 2.33 in commit
27a50d6755bae906bc73b4ec1a8b448467f0bea1. Thanks to Christian and Simon
for helping me with the patch archaeology.

According to Documentation/process/changes.rst, the minimum supported
version of binutils is 2.33. Since all supported versions of GAS support
this instruction, drop the assembler invocation, preprocessor
flags/guards, and the cross assembler macro that's now unused.

This also avoids a recursive self reference in a follow up cleanup
patch.

Cc: Christian Biesinger <redacted>
Cc: Simon Marchi <redacted>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>

This change looks good, but I think we should do the same for the gcc
version check:

-#if __LINUX_ARM_ARCH__ >= 8 && defined(CONFIG_AS_DMB_ISHLD)
+#if __LINUX_ARM_ARCH__ >= 8
 #define aarch32_smp_mb()       dmb(ish)
 #define aarch32_smp_rmb()      dmb(ishld)
 #define aarch32_smp_wmb()      dmb(ishst)

gcc-4.8 already supported -march=armv8, and we require gcc-5.1 now, so both
this #if/#else construct and the corresponding "cc32-option,-march=armv8-a"
check should be obsolete now.

       Arnd

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