arm64: Do not include __READ_ONCE() block in assembly files

When building arm64 defconfig + CONFIG_LTO_CLANG_{FULL,THIN}=y after
commit 558c303c9734 ("arm64: Mitigate spectre style branch history side
channels"), the following error occurs:

  <instantiation>:4:2: error: invalid fixup for movz/movk instruction
   mov w0, #ARM_SMCCC_ARCH_WORKAROUND_3
   ^

Marc figured out that moving "#include <linux/init.h>" in
include/linux/arm-smccc.h into a !__ASSEMBLY__ block resolves it. The
full include chain with CONFIG_LTO=y from include/linux/arm-smccc.h:

include/linux/init.h
include/linux/compiler.h
arch/arm64/include/asm/rwonce.h
arch/arm64/include/asm/alternative-macros.h
arch/arm64/include/asm/assembler.h

The asm/alternative-macros.h include in asm/rwonce.h only happens when
CONFIG_LTO is set, which ultimately casues asm/assembler.h to be
included before the definition of ARM_SMCCC_ARCH_WORKAROUND_3. As a
result, the preprocessor does not expand ARM_SMCCC_ARCH_WORKAROUND_3 in
__mitigate_spectre_bhb_fw, which results in the error above.

Avoid this problem by just avoiding the CONFIG_LTO=y __READ_ONCE() block
in asm/rwonce.h with assembly files, as nothing in that block is useful
to assembly files, which allows ARM_SMCCC_ARCH_WORKAROUND_3 to be
properly expanded with CONFIG_LTO=y builds.

Fixes: e35123d83ee3 ("arm64: lto: Strengthen READ_ONCE() to acquire when CONFIG_LTO=y")
Cc: <[email protected]> # 5.11.x
Link: https://lore.kernel.org/r/[email protected]/
Reported-by: Marc Zyngier <[email protected]>
Acked-by: James Morse <[email protected]>
Signed-off-by: Nathan Chancellor <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Catalin Marinas <[email protected]>

0 files changed, 0 insertions, 0 deletions