Re: [kbuild-all] Re: gcc-5: error: -gz is not supported in this configuration

[Fangrui Song]

> But if that gcc was originally
> _configured_ with a version of binutils that doesn't support -gz=zlib,

I agree with this theory :)

On 2020-06-10, Arvind Sankar wrote:
> On Tue, Jun 09, 2020 at 11:23:31PM -0400, Arvind Sankar wrote:
> > On Tue, Jun 09, 2020 at 11:12:25PM -0400, Arvind Sankar wrote:
> > > The output of gcc-5 -dumpspecs may also be useful.
> > >
> > > The exact Kconfig check should have been
> > > 	gcc-5 -Werror -gz=zlib -S -x c /dev/null -o /dev/null
> > >
> > > I can't see how that would succeed if the a.c test didn't but maybe just
> > > in case?
> >
> > Oh wait, -S instead of -c. Which means it runs neither the assembler nor
> > the linker, so gcc won't error out. But if that gcc was originally
> > _configured_ with a version of binutils that doesn't support -gz=zlib,
> > it will give an error on -c regardless of whether the runtime binutils
> > would actually support it or not.
>
> I think the below might be better than passing the option via -Wa, since
> gcc will translate -gz=zlib into the right assembler option anyway, and
> it will also generate an error if the compiler driver was misconfigured
> and won't support the option even if the rest of the toolchain does,
> fixing the config dependency.
>
> Unless this doesn't work with Clang?

Clang>=6 supports -gz=zlib

> Alternatively (or even in addition), we should redefine cc-option to use
> -c, it uses -S in the Kconfig version, apparently for speed, but -c in
> the Kbuild version.

Unifying cc-option in scripts/Kbuild.include & scripts/Kconfig.include
sounds good.

> diff --git a/Makefile b/Makefile
> index 839f9fee22cb..cb29e56f227a 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -842,7 +842,7 @@ endif
>
> ifdef CONFIG_DEBUG_INFO_COMPRESSED
> DEBUG_CFLAGS	+= -gz=zlib
> -KBUILD_AFLAGS	+= -Wa,--compress-debug-sections=zlib
> +KBUILD_AFLAGS	+= -gz=zlib
> KBUILD_LDFLAGS	+= --compress-debug-sections=zlib
> endif
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index cb98741601bd..94ce36be470c 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -229,7 +229,7 @@ config DEBUG_INFO_COMPRESSED
> 	bool "Compressed debugging information"
> 	depends on DEBUG_INFO
> 	depends on $(cc-option,-gz=zlib)
> -	depends on $(as-option,-Wa$(comma)--compress-debug-sections=zlib)
> +	depends on $(as-option,-gz=zlib)
> 	depends on $(ld-option,--compress-debug-sections=zlib)
> 	help
> 	  Compress the debug information using zlib.  Requires GCC 5.0+ or Clang

This patch looks good.

(clang cc1as only supports(hardcodes) a limited number of -Wa, options
(it parses the options by itself, rather than delegating to GNU as like
GCC). If there is a compiler driver option, that is usually preferable)