Re: [PATCH] kconfig: detect LD implementation

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Mar 16, 2022 at 11:28:48AM +0100, Michal Orzel wrote:
> Hi Roger,
> 
> On 14.03.2022 11:55, Roger Pau Monne wrote:
> > Detect GNU and LLVM ld implementations. This is required for further
> > patches that will introduce diverging behaviour depending on the
> > linker implementation in use.
> > 
> > Note that LLVM ld returns "compatible with GNU linkers" as part of the
> > version string, so be on the safe side and use '^' to only match at
> > the start of the line in case LLVM ever decides to change the text to
> > use "compatible with GNU ld" instead.
> > 
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > ---
> >  xen/Kconfig | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/xen/Kconfig b/xen/Kconfig
> > index d134397a0b..e8d5e70d46 100644
> > --- a/xen/Kconfig
> > +++ b/xen/Kconfig
> > @@ -23,6 +23,12 @@ config CLANG_VERSION
> >     int
> >     default $(shell,$(BASEDIR)/scripts/clang-version.sh $(CC))
> >  
> > +config LD_IS_GNU
> > +   def_bool $(success,$(LD) --version | head -n 1 | grep -q "^GNU ld")
> > +> +config LD_IS_LLVM
> > +   def_bool $(success,$(LD) --version | head -n 1 | grep -q "^LLD")
> > +
> >  # -fvisibility=hidden reduces -fpic cost, if it's available
> >  config CC_HAS_VISIBILITY_ATTRIBUTE
> >     def_bool $(cc-option,-fvisibility=hidden)
> 
> NIT: You do not really need to use head especiialy if grep for the beginning 
> of a line.

I'm afraid I don't agree. We use head because we only want to match
against the first line of the output, and then we use '^' to match at
the beginning of such line. Without using head we would end up
matching at the beginning of any line present in the output.

Thanks, Roger.