Re: riscv: alternatives: move length validation inside the subsection

[Nathan Chancellor <nathan@kernel.org>]

On Thu, Jun 02, 2022 at 07:27:34PM +0800, Changbin Du wrote:
> Apply the same fix from commit 966a0acce2fc ("arm64/alternatives: move
> length validation inside the subsection") to riscv.  Due to the one-pass
> design of LLVM's integrated assembler, it can not compute the length of
> instructions if the .org directive is outside of the subsection that these
> instructions are in.
> 
> Here is the build error reported by llvm:
> 
> In file included from ./arch/riscv/include/asm/pgtable.h:108:
> ./arch/riscv/include/asm/tlbflush.h:23:2: error: expected assembly-time absolute expression
>         ALT_FLUSH_TLB_PAGE(__asm__ __volatile__ ("sfence.vma %0" : : "r" (addr) : "memory"));
>         ^
> ./arch/riscv/include/asm/errata_list.h:41:5: note: expanded from macro 'ALT_FLUSH_TLB_PAGE'
> asm(ALTERNATIVE("sfence.vma %0", "sfence.vma", SIFIVE_VENDOR_ID,        \
>     ^
> ./arch/riscv/include/asm/alternative-macros.h:187:2: note: expanded from macro 'ALTERNATIVE'
>         _ALTERNATIVE_CFG(old_content, new_content, vendor_id, errata_id, CONFIG_k)
>         ^
> ./arch/riscv/include/asm/alternative-macros.h:113:2: note: expanded from macro '_ALTERNATIVE_CFG'
>         __ALTERNATIVE_CFG(old_c, new_c, vendor_id, errata_id, IS_ENABLED(CONFIG_k))
>         ^
> ./arch/riscv/include/asm/alternative-macros.h:110:2: note: expanded from macro '__ALTERNATIVE_CFG'
>         ALT_NEW_CONTENT(vendor_id, errata_id, enable, new_c)
>         ^
> ./arch/riscv/include/asm/alternative-macros.h:98:3: note: expanded from macro 'ALT_NEW_CONTENT'
>         ".org   . - (887b - 886b) + (889b - 888b)\n"                    \
>          ^
> <inline asm>:25:6: note: instantiated into assembly here
> .org    . - (887b - 886b) + (889b - 888b)
>         ^
> 
> Signed-off-by: Changbin Du <changbin.du@gmail.com>

Thanks for the patch! I already sent an equivalent change two weeks ago
as https://lore.kernel.org/20220516214520.3252074-1-nathan@kernel.org/,
which I think is slightly better because it handles the __ASSEMBLY__
version of the macro as well.

Cheers,
Nathan

> ---
>  arch/riscv/include/asm/alternative-macros.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/include/asm/alternative-macros.h b/arch/riscv/include/asm/alternative-macros.h
> index e13b1f6bb400..c7d7f1945768 100644
> --- a/arch/riscv/include/asm/alternative-macros.h
> +++ b/arch/riscv/include/asm/alternative-macros.h
> @@ -94,9 +94,9 @@
>  	new_c "\n"							\
>  	".option pop\n"							\
>  	"889 :\n"							\
> -	".previous\n"							\
>  	".org	. - (887b - 886b) + (889b - 888b)\n"			\
>  	".org	. - (889b - 888b) + (887b - 886b)\n"			\
> +	".previous\n"							\
>  	".endif\n"
>  
>  #define __ALTERNATIVE_CFG(old_c, new_c, vendor_id, errata_id, enable)	\
> -- 
> 2.26.2
>