Re: Avoid gnulib redefinitions - MDA, free-posix

[Gavin Smith]

On Sat, Oct 29, 2022 at 09:58:25AM -0700, Paul Eggert wrote:
> If it's just 'free', I might prefer the latter solution, to underline the
> special case and to avoid even more complexity in gnulib-tool. Is that
> something you could write?

Here is a first attempt.  I am not very familiar with the Gnulib code.

The main idea is to put a define in AM_CPPFLAGS in the Makefile that
gnulib-tool generates.  Then the gnulib headers can distinguish whether
they are being used as part of building gnulib, or building the user's
program.

This avoided looking through all the gnulib code and deciding where
to replace "free" with "gl_internal_free" or whatever the replacement
would be called.

I tried to minimize the number of lines of code that would change, but
if this approach was adopted, then the following changes should also be
made:
* Rename free-posix to free-posix-internal and free-posix-public to free-posix
* REPLACE_FREE to be changed to REPLACE_FREE_INTERNAL throughout gnulib,
  likewise REPACE_FREE_PUBLIC to REPLACE_FREE.

I tested this on a project with a gnulib import.

Let me know if this is the right approach and if there are changes to
make to the patch.

diff --git a/ChangeLog b/ChangeLog
index 6f4bea5c1c..994f457e70 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,21 @@
+2020-10-29  Gavin Smith  
+
+   Avoid unrequested 'free' redefinition
+
+   * gnulib-tool (func_emit_lib_Makefile_am):
+   Add -DGNULIB_INTERNAL to AM_CPPFLAGS.
+   * m4/free-public.m4, modules/free-posix-public:
+   New module to set @REPLACE_FREE_PUBLIC@ from @REPLACE_FREE@.
+   * modules/stdlib, m4/stdlib_h.m4:
+   Substitute for @REPLACE_FREE_PUBLIC@.
+   * lib/stdlib.in.h <@GNULIB_FREE_POSIX@>: Only replace 'free' if
+   both GNULIB_INTERNAL and @REPLACE_FREE@ are set, or if
+   @REPLACE_FREE_PUBLIC@ is set.
+
+   This allows Gnulib to use the free redefinition internally without
+   replacing it in user code, unless they explicitly request the
+   module.
+
 2022-10-23  Bruno Haible  
 
assert-h: Make static_assert work on Solaris 11.4.
diff --git a/gnulib-tool b/gnulib-tool
index 028bcf36ad..84a77171d7 100755
--- a/gnulib-tool
+++ b/gnulib-tool
@@ -3945,7 +3945,7 @@ func_emit_lib_Makefile_am ()
   fi
   if test -z "$makefile_name"; then
 echo
-echo "AM_CPPFLAGS =$cppflags_part1$cppflags_part2"
+echo "AM_CPPFLAGS = -DGNULIB_INTERNAL$cppflags_part1$cppflags_part2"
 echo "AM_CFLAGS ="
   else
 if test -n "$cppflags_part1$cppflags_part2"; then
diff --git a/lib/stdlib.in.h b/lib/stdlib.in.h
index 8e0a609f1f..f75b8621f4 100644
--- a/lib/stdlib.in.h
+++ b/lib/stdlib.in.h
@@ -179,7 +179,7 @@ _GL_WARN_ON_USE (_Exit, "_Exit is unportable - "
 
 
 #if @GNULIB_FREE_POSIX@
-# if @REPLACE_FREE@
+# if @REPLACE_FREE@ && defined(GNULIB_INTERNAL) || @REPLACE_FREE_PUBLIC@
 #  if !(defined __cplusplus && defined GNULIB_NAMESPACE)
 #   undef free
 #   define free rpl_free
diff --git a/m4/free-public.m4 b/m4/free-public.m4
new file mode 100644
index 00..497abf81ae
--- /dev/null
+++ b/m4/free-public.m4
@@ -0,0 +1 @@
+AC_DEFUN([gl_PREREQ_FREE_PUBLIC], [:])
diff --git a/m4/stdlib_h.m4 b/m4/stdlib_h.m4
index 9e2096976f..b096054284 100644
--- a/m4/stdlib_h.m4
+++ b/m4/stdlib_h.m4
@@ -171,6 +171,7 @@ AC_DEFUN([gl_STDLIB_H_DEFAULTS],
   REPLACE_CALLOC_FOR_CALLOC_POSIX=0;  
AC_SUBST([REPLACE_CALLOC_FOR_CALLOC_POSIX])
   REPLACE_CANONICALIZE_FILE_NAME=0;  AC_SUBST([REPLACE_CANONICALIZE_FILE_NAME])
   REPLACE_FREE=0;AC_SUBST([REPLACE_FREE])
+  REPLACE_FREE_PUBLIC=0; AC_SUBST([REPLACE_FREE_PUBLIC])
   REPLACE_INITSTATE=0;   AC_SUBST([REPLACE_INITSTATE])
   REPLACE_MALLOC_FOR_MALLOC_GNU=0;AC_SUBST([REPLACE_MALLOC_FOR_MALLOC_GNU])
   REPLACE_MALLOC_FOR_MALLOC_POSIX=0;  
AC_SUBST([REPLACE_MALLOC_FOR_MALLOC_POSIX])
diff --git a/modules/free-posix-public b/modules/free-posix-public
new file mode 100644
index 00..050a06bf76
--- /dev/null
+++ b/modules/free-posix-public
@@ -0,0 +1,27 @@
+Description:
+Work around systems where free clobbers errno.
+
+Files:
+m4/free-public.m4
+
+Depends-on:
+free-posix
+
+configure.ac:
+REPLACE_FREE_PUBLIC=$REPLACE_FREE
+gl_CONDITIONAL([GL_COND_OBJ_FREE_PUBLIC], [test $REPLACE_FREE_PUBLIC = 1])
+AM_COND_IF([GL_COND_OBJ_FREE_PUBLIC], [
+  gl_PREREQ_FREE_PUBLIC
+])
+gl_STDLIB_MODULE_INDICATOR([free-posix-public])
+
+Makefile.am:
+
+Include:
+
+
+License:
+LGPLv2+
+
+Maintainer:
+None
diff --git a/modules/stdlib b/modules/stdlib
index 45d8f59331..2266e68d52 100644
--- a/modules/stdlib
+++ b/modules/stdlib
@@ -131,6 +131,7 @@ stdlib.h: stdlib.in.h $(top_builddir)/config.status 
$(CXXDEFS_H) \
  -e 
's|@''REPLACE_CALLOC_FOR_CALLOC_POSIX''@|$(REPLACE_CALLOC_FOR_CALLOC_POSIX)|g' \
  -e 
's|@''REPLACE_CANONICALIZE_FILE_NAME''@|$(REPLACE_CANONICALIZE_FILE_NAME)|g' \
  -e 's|@''REPLACE_FREE''@|$(REPLACE_FREE)|g' \
+ -e 's|@''REPLACE_FREE_PUBLIC''@|$(REPLACE_FREE_PUBLIC)|g' \

Re: Avoid gnulib redefinitions - MDA, free-posix

[Paul Eggert]

On 2022-10-29 06:36, Gavin Smith wrote:

Here is one idea.  When
using a module like 'free-posix', if it is loaded as a dependency only,
use the redefinition in Gnulib code only, but do not override symbols
in user code.  It would be as if there were two modules, say
gl-free-posix and free-posix, where gl-free-posix made the redefinition
of rpl_gl_free and free-posix (requested by the user) redirected rpl_free
to rpl_gl_free.


If it's just 'free', I might prefer the latter solution, to underline 
the special case and to avoid even more complexity in gnulib-tool. Is 
that something you could write?


If this problem occurs with lots of other symbols perhaps we'd need 
something more like the former, though. This would need more hacking, I 
expect.

Avoid gnulib redefinitions - MDA, free-posix

[Gavin Smith]

Previously in the Texinfo project, we added variables to configure.ac to
stop the redefinition of "Microsoft deprecated aliases":

https://lists.gnu.org/archive/html/bug-gnulib/2021-03/msg4.html

For example, GNULIB_MDA_FDOPEN to stop the redefinition of 'fdopen'.

Recently, it was reported that this didn't work when building on
MS-Windows.  I found that it should maybe be GL_GNULIB_MDA_FDOPEN instead:

https://lists.gnu.org/archive/html/bug-texinfo/2022-10/msg00180.html

I had identified the following change as potentially being responsible:

2021-04-11  Bruno Haible  

Support several gnulib-tool invocations under the same configure.ac.
Reported by Reuben Thomas  in
.  
This is done by defining the Gnulib module indicator variables per
gnulib-tool invocation. So that a generated .h file is no longer
influenced by the set of modules used in other gnulib-tool invocations. 
* gnulib-tool (func_compute_include_guard_prefix): Set
module_indicator_prefix.

Should we use the variables with the GL_ prefix now and is this something
we can rely on?  Or should we simply #undef fdopen and the other symbols?

We don't use fdopen, putenv or mktemp in the library being built, but these
are pulled in by Gnulib dependencies.

I don't know if it is possible at all but it would seem to be better
for Gnulib not to redefine symbols that are not actually used in the
program.  I'd like to keep the use of Gnulib code to a minimum, only
using it where there is a significant portability benefit.

Likewise, there is a warning about the redefinition of "free", that
comes from the free-posix module.  The issue is, when building a
Perl extension module, some source files include Perl headers that
also redefine "free".

free-posix is to work around the possibility that free overwrites
the value of errno.  It's unlikely that this would cause a problem
in our code, but free-posix is required internally by Gnulib code.

It seems undesirable to override such a simple function as 'free',
when this is not something the user has asked for - as in our case,
it caused a conflict with other uses (Perl headers).

This may be hard for you to change, though.  Here is one idea.  When
using a module like 'free-posix', if it is loaded as a dependency only,
use the redefinition in Gnulib code only, but do not override symbols
in user code.  It would be as if there were two modules, say
gl-free-posix and free-posix, where gl-free-posix made the redefinition
of rpl_gl_free and free-posix (requested by the user) redirected rpl_free
to rpl_gl_free.