From f47462c9d8af437ae7d3ef410cf11513f5e3714c Mon Sep 17 00:00:00 2001 From: Bill Wendling Date: Fri, 20 Nov 2020 14:40:34 -0800 Subject: [PATCH] powerpc: Work around inline asm issues in alternate feature sections The clang toolchain treats inline assembly a bit differently than straight assembly code. In particular, inline assembly doesn't have the complete context available to resolve expressions. This is intentional to avoid divergence in the resulting assembly code. We can work around this issue by borrowing a workaround done for ARM, i.e. not directly testing the labels themselves, but by moving the current output pointer by a value that should always be zero. If this value is not null, then we will trigger a backward move, which is explicitly forbidden. Signed-off-by: Bill Wendling [mpe: Put it in a macro and only do the workaround for clang] Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20201120224034.191382-4-morbo@google.com --- arch/powerpc/include/asm/feature-fixups.h | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) diff --git a/arch/powerpc/include/asm/feature-fixups.h b/arch/powerpc/include/asm/feature-fixups.h index fbd406cd6916..c509f784a5f6 100644 --- a/arch/powerpc/include/asm/feature-fixups.h +++ b/arch/powerpc/include/asm/feature-fixups.h @@ -36,6 +36,24 @@ label##2: \ .align 2; \ label##3: + +#ifndef CONFIG_CC_IS_CLANG +#define CHECK_ALT_SIZE(else_size, body_size) \ + .ifgt (else_size) - (body_size); \ + .error "Feature section else case larger than body"; \ + .endif; +#else +/* + * If we use the ifgt syntax above, clang's assembler complains about the + * expression being non-absolute when the code appears in an inline assembly + * statement. + * As a workaround use an .org directive that has no effect if the else case + * instructions are smaller than the body, but fails otherwise. + */ +#define CHECK_ALT_SIZE(else_size, body_size) \ + .org . + ((else_size) > (body_size)); +#endif + #define MAKE_FTR_SECTION_ENTRY(msk, val, label, sect) \ label##4: \ .popsection; \ @@ -48,9 +66,7 @@ label##5: \ FTR_ENTRY_OFFSET label##2b-label##5b; \ FTR_ENTRY_OFFSET label##3b-label##5b; \ FTR_ENTRY_OFFSET label##4b-label##5b; \ - .ifgt (label##4b- label##3b)-(label##2b- label##1b); \ - .error "Feature section else case larger than body"; \ - .endif; \ + CHECK_ALT_SIZE((label##4b-label##3b), (label##2b-label##1b)); \ .popsection; -- 2.11.0