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

[Kees Cook <keescook@chromium.org>]

On Wed, Aug 30, 2023 at 08:36:46AM -0700, Nathan Chancellor wrote:
> On Wed, Aug 30, 2023 at 06:22:45AM -0700, Palmer Dabbelt wrote:
> > On Wed, 16 Aug 2023 10:35:43 PDT (-0700), nathan@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@intel.com>
> > > Closes: https://lore.kernel.org/all/202308090204.9yZffBWo-lkp@intel.com/
> > > Signed-off-by: Nathan Chancellor <nathan@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@rivosinc.com>
> > Acked-by: Palmer Dabbelt <palmer@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.

Agreed -- got for it. :)

-- 
Kees Cook