Re: [PATCH] riscv/runtime-const: Disable linker relaxation for RUNTIME_MAGIC

[Nathan Chancellor <nathan@kernel.org>]

On Sun, Aug 02, 2026 at 10:43:42AM -0700, Fangrui Song wrote:
> Commit ee10b1028129 ("riscv/runtime-const: Replace open-coded
> placeholder with RUNTIME_MAGIC") switched the lui + addi[w] placeholder
> from hand-encoded immediates to %hi()/%lo() of RUNTIME_MAGIC.
> 
> GNU Assembler folds %hi()/%lo() of an absolute expression at assembly
> time. LLVM's integrated assembler since 21.1 defers it to the linker
> instead, which range checks it: on riscv64 R_RISCV_HI20 must fit a
> signed 20-bit field, and RUNTIME_MAGIC (0x89ABCDEF) is a positive 64-bit
> value rather than a sign-extended 32-bit one, so it does not:
> 
>     ld.lld: error: relocation R_RISCV_HI20 out of range: 563901 is not in
>     [-524288, 524287]
> 
> The sequence is patched at runtime and its instruction offsets are
> recorded via ".long 1b - .", so the linker must not touch it in the
> first place. Add ".option norelax", as is already done for
> ALTERNATIVE() and static keys; the integrated assembler then resolves
> %hi()/%lo() itself and emits no relocation, restoring the exact
> encoding the open-coded placeholder produced.
> 
> Fixes: ee10b1028129 ("riscv/runtime-const: Replace open-coded placeholder with RUNTIME_MAGIC")
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Closes: https://github.com/ClangBuiltLinux/linux/issues/2179
> Signed-off-by: Fangrui Song <i@maskray.me>

Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>

Thanks a lot for the quick fix!

> ---
> Applies to tip/locking/core; the RISC-V tree (riscv/linux.git) does not
> carry ee10b1028129.
> 
>  arch/riscv/include/asm/runtime-const.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/runtime-const.h b/arch/riscv/include/asm/runtime-const.h
> index a472ebbf0971..ce2008bb5227 100644
> --- a/arch/riscv/include/asm/runtime-const.h
> +++ b/arch/riscv/include/asm/runtime-const.h
> @@ -23,6 +23,7 @@
>  	typeof(sym) __ret;						\
>  	asm_inline(".option push\n\t"					\
>  		".option norvc\n\t"					\
> +		".option norelax\n\t"					\
>  		"1:\t"							\
>  		"lui	%[__ret], %%hi(" RUNTIME_MAGIC ")\n\t"		\
>  		"addi	%[__ret],%[__ret], %%lo(" RUNTIME_MAGIC ")\n\t"	\
> @@ -47,6 +48,7 @@
>  #define RISCV_RUNTIME_CONST_64_PREAMBLE				\
>  	".option push\n\t"					\
>  	".option norvc\n\t"					\
> +	".option norelax\n\t"					\
>  	"1:\t"							\
>  	"lui	%[__ret], %%hi(" RUNTIME_MAGIC ")\n\t"		\
>  	"lui	%[__tmp], %%hi(" RUNTIME_MAGIC ")\n\t"		\
> 
> base-commit: 5e601ab3615c86be7c4068ce992f94654693a032
> -- 
> 2.43.0
> 
> 

-- 
Cheers,
Nathan