Re: CC and CFLAGS are ignored by part of the build

[Gavin Smith]

On Tue, Nov 14, 2023 at 02:22:00PM +0200, Eli Zaretskii wrote:
> AFAIU, that's impossible in general, because CFLAGS could include
> flags that cannot be applied to both CC and PERL_CONF_cc due to
> compatibility issues, since Perl could have been built using a very
> different compiler.
> 
> IMNSHO, it isn't a catastrophe that compiling Perl extensions needs a
> separate C flags variable.  It is basically similar to CFLAGS and
> CXXFLAGS being separate for building the same project (which happens
> inj practice, for example, in GDB, which is part C and part C++).  And
> if the GCS doesn't cater for these (relatively rare and specialized)
> situations, then I think the GCS needs to be amended.  There's no need
> to be dogmatic about this.
> 

These variables were mentioned in the output of ./configure --help
but we never documented anywhere why they were needed, as far as I could
tell.  I've added text to the INSTALL file:

+  When `configure' is running in the XS subdirectory, instead of the
+  standard CC, CFLAGS, LDFLAGS etc., it uses special variables with a
+  PERL_EXT_ prefix.  These are all listed in the output of `configure
+  --help'.  This is necessary because it is possible that the C compiler
+  being used to compile Perl extension modules is a different compiler
+  to that used for the rest of the package.  (However, if you need to
+  override these variables when running `make', use the unprefixed
+  variants, e.g. CFLAGS instead of PERL_EXT_CFLAGS.  Exception: you
+  cannot override CPPFLAGS this way as gnulib uses this variable.)