Re: [PATCH 2/2] Makefile: Only specify '--prefix=' when building with clang + GNU as

[Nick Desaulniers <ndesaulniers@google.com>]

On Tue, Mar 2, 2021 at 2:02 PM Fangrui Song <maskray@google.com> wrote:
>
> On 2021-03-02, Nathan Chancellor wrote:
> >When building with LLVM_IAS=1, there is no point to specifying
> >'--prefix=' because that flag is only used to find the cross assembler,
> >which is clang itself when building with LLVM_IAS=1. All of the other
> >tools are invoked directly from PATH or a full path specified via the
> >command line, which does not depend on the value of '--prefix='.
> >
> >Sharing commands to reproduce issues becomes a little bit easier without
> >a '--prefix=' value because that '--prefix=' value is specific to a
> >user's machine due to it being an absolute path.
> >
> >Signed-off-by: Nathan Chancellor <nathan@kernel.org>
>
> Reviewed-by: Fangrui Song <maskray@google.com>
>
> clang can spawn GNU as (if -f?no-integrated-as is specified) and GNU
> objcopy (-f?no-integrated-as and -gsplit-dwarf and -g[123]).

But -g get's set via CONFIG_DEBUG_INFO and -gsplit-dwarf by
DEBUG_INFO_SPLIT.  So if we say:
$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang LLVM_IAS=1

So cross compile, use clang, use the integrated assembler (ie. with
this change, don't set --prefix), with either of the two above
configs, which objcopy get's exec'd?

>
> With LLVM_IAS=1, these cases are ruled out.



-- 
Thanks,
~Nick Desaulniers