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

[Nathan Chancellor]

On Wed, Aug 30, 2023 at 06:22:45AM -0700, Palmer Dabbelt wrote:
> 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.

I don't think lib/Kconfig.debug has a formal maintainer. Given that and
the fact that this change only affects RISC-V, I think it is entirely
reasonable for you to take it.

Cheers,
Nathan