Hi Bill,
Bill Wendling <mo...@google.com> writes:
> 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 <mo...@google.com>
> ---
> arch/powerpc/include/asm/feature-fixups.h | 17 +++++++++++++----
> 1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/feature-fixups.h
> b/arch/powerpc/include/asm/feature-fixups.h
> index b0af97add751..f81036518edb 100644
> --- a/arch/powerpc/include/asm/feature-fixups.h
> +++ b/arch/powerpc/include/asm/feature-fixups.h
> @@ -36,6 +36,18 @@ label##2: \
> .align 2; \
> label##3:
>
> +/*
> + * If the .org directive fails, it means that the feature instructions
> + * are smaller than the alternate instructions. This used to be written
> + * as
> + *
> + * .ifgt (label##4b-label##3b) - (label##2b-label##1b)
> + * .error "Feature section else case larger than body"
> + * .endif
> + *
> + * but clang's assembler complains about the expression being non-absolute
> + * when the code appears in an inline assembly statement.
> + */
> #define MAKE_FTR_SECTION_ENTRY(msk, val, label, sect) \
> label##4: \
> .popsection; \
> @@ -48,12 +60,9 @@ 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; \
> + .org . - ((label##4b-label##3b) > (label##2b-label##1b)); \
> .popsection;
When I have an oversize alt section this doesn't seem to give me any
error using binutils?
If I hard code:
.org . - (1);
It fails as expected.
But if I hard code:
.org . - (1 > 0);
It builds?
cheers
