[PATCH] lib/Kconfig.debug: Restrict DEBUG_INFO_SPLIT for RISC-V

[Palmer Dabbelt]

On Wed, 16 Aug 2023 10:35:43 PDT (-0700), nathan at kernel.org wrote:
> When building for ARCH=riscv using LLVM < 14, there is an error with
> CONFIG_DEBUG_INFO_SPLIT=y:
>
>   error: A dwo section may not contain relocations
>
> This was worked around in LLVM 15 by disallowing '-gsplit-dwarf' with
> '-mrelax' (the default), so CONFIG_DEBUG_INFO_SPLIT is not selectable
> with newer versions of LLVM:
>
>   $ clang --target=riscv64-linux-gnu -gsplit-dwarf -c -o /dev/null -x c /dev/null
>   clang: error: -gsplit-dwarf is unsupported with RISC-V linker relaxation (-mrelax)
>
> GCC silently had a similar issue that was resolved with GCC 12.x.
> Restrict CONFIG_DEBUG_INFO_SPLIT for RISC-V when using LLVM or GCC <
> 12.x to avoid these known issues.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1914
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99090
> Reported-by: kernel test robot <lkp at intel.com>
> Closes: https://lore.kernel.org/all/202308090204.9yZffBWo-lkp@intel.com/
> Signed-off-by: Nathan Chancellor <nathan at kernel.org>
> ---
> Since this only impacts RISC-V, it seems reasonable that this would go
> in via their tree but I have added Andrew in case he wants to take it.
> ---
>  lib/Kconfig.debug | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index d6798513a8c2..bd51274f4771 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -355,6 +355,11 @@ endchoice # "Compressed Debug information"
>  config DEBUG_INFO_SPLIT
>  	bool "Produce split debuginfo in .dwo files"
>  	depends on $(cc-option,-gsplit-dwarf)
> +	# RISC-V linker relaxation + -gsplit-dwarf has issues with LLVM and GCC
> +	# prior to 12.x:
> +	# https://github.com/llvm/llvm-project/issues/56642
> +	# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99090
> +	depends on !RISCV || GCC_VERSION >= 120000
>  	help
>  	  Generate debug info into separate .dwo files. This significantly
>  	  reduces the build directory size for builds with DEBUG_INFO,

Reviewed-by: Palmer Dabbelt <palmer at rivosinc.com>
Acked-by: Palmer Dabbelt <palmer at rivosinc.com>

Not sure who's taking stuff for lib/Kconfig.debug, I can take it via the 
RISC-V tree if folks are OK with it.  Kees and Andrew were the last to 
touch it.

>
> ---
> base-commit: 2ccdd1b13c591d306f0401d98dedc4bdcd02b421
> change-id: 20230816-riscv-debug_info_split-0713571a1ac2
>
> Best regards,