Re: [PATCH] x86/boot: Fix build with LLVM toolchain

["Alejandro Vallejo" <alejandro.vallejo@cloud.com>]

On Tue Nov 5, 2024 at 7:23 PM GMT, Andrew Cooper wrote:
> On 05/11/2024 2:55 pm, Frediano Ziglio wrote:
> > diff --git a/xen/tools/combine_two_binaries.py b/xen/tools/combine_two_binaries.py
> > index 447c0d3bdb..79ae8900b1 100755
> > --- a/xen/tools/combine_two_binaries.py
> > +++ b/xen/tools/combine_two_binaries.py
> > @@ -67,13 +67,22 @@ if args.exports is not None:
> >  
> >  # Parse mapfile, look for ther symbols we want to export.
> >  if args.mapfile is not None:
> > -    symbol_re = re.compile(r'\s{15,}0x([0-9a-f]+)\s+(\S+)\n')
> > +    symbol_re_clang = \
> > +        re.compile(r'\s+([0-9a-f]+)\s+([0-9a-f]+)\s+([0-9a-f]+)\s+([0-9a-f]+)\s{15,}(\S+)\n')
> > +    symbol_re_gnu = re.compile(r'\s{15,}0x([0-9a-f]+)\s+(\S+)\n')
>
> These are specific to the linker, not the compiler, so really should be
> _ld and _lld rather than _gnu and _clang.

GNU binutils ships not one, but two linkers. _ld does not reflect the fact that
it's not the map format of a linker, but a family of them. Probably shared by
mold too. That's a good reason for _gnu to stay _gnu (or if changing, to
_binutils; but that's hardly relevant in this patch).

Otherwise _clang could become either _llvm or _lld. Given there's a single
linker shipped by LLVM the difference is less than cosmetic.

>
> The build environment does have CONFIG_LD_IS_GNU which is used for one
> LD vs LLD distinction.  It seems reasonable to re-use it here (so you're
> not trying both regexes in the hope that one works), although you'll
> need to plumb it into the script somehow because it's not exported into
> the environment currently.
>
>
> But, regexes are utterly opaque, and given that neither Binutils nor
> LLVM document their map format, you really need to provide at least one
> example of what a relevant mapfile looks like in a comment.
>
> Looking at built-in-32.offset.map in it's gnu form, it's presumably
> looking for the lines that are just a hex address and a name with no
> other punctuation.
>
> But the lld form is clearly different.
>
> ~Andrew

Cheers,
Alejandro