Re: [PATCH 2/2] libcpp: Avoid remapping filenames within directives

[Richard Purdie <richard.purdie@linuxfoundation.org>]

On Tue, 2022-11-01 at 13:32 -0600, Jeff Law wrote:
> On 8/17/22 06:15, Richard Purdie via Gcc-patches wrote:
> > Code such as:
> #include __FILE__
> > 
> > can interact poorly with file-prefix-map options when cross compiling. In
> > general you're after to remap filenames for use in target context but the
> > local paths should be used to find include files at compile time. Ingoring
> > filename remapping for directives is one way to avoid such failures.
> > 
> > libcpp/ChangeLog:
> > 
> >      * macro.cc (_cpp_builtin_macro_text): Don't remap filenames within directives
> 
> So I went back and reviewed the old PR which introduced this code.  It 
> was actually the Yocto project that got this code in to begin with :-)

Thanks for the review!

That sounds right, we use it heavily and originally had a few issues in
this area. It now generally works really well, we just found this
corner case :)
  
> There wasn't really any discussion AFAICT about whether or not to remap 
> in directives that I saw in the PR.

I don't think we'd realised there was this corner case. Now we have
found code doing it, I think the behaviour we should have is fairly
clear which is why we're sending the patch.

> ISTM that given the change in behavior, we should probably document that 
> we don't remap in directives.  Probably doc/invoke.texi.
> 
> With suitable documentation, this should be fine.  It seems like it 
> ought to be independent of the first patch in this series which adds 
> support for remapping relative paths.

Thanks for merging 1/2, it was independent, just related as a path
mapping issue we found. I'll keep the coding style in mind in future.

I've sent a new version of this patch which updates doc/invoke.texi,
just adding to file-prefix-map as the others all reference it.

Cheers,

Richard