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Re: visibility.m4

From: Simon Josefsson
Subject: Re: visibility.m4
Date: Tue, 12 Jan 2010 15:06:58 +0100
User-agent: Gnus/5.110011 (No Gnus v0.11) Emacs/23.1 (gnu/linux)

Mike Gran <address@hidden> writes:

> Hello-
> If I use visibility.m4 on a platform with a recent GCC (4.x) on 
> Cygwin, the visibility.m4 correctly discovers that gcc can compile with 
> -fvisibility="hidden".  But, on Cygwin (and probably most non-ELF) gcc does 
> not actualy implement the visibility and emits the warning "visibility 
> attribute not supported in this configuration" instead.  Even so, the tests 
> in visibility.m4 pass, and HAVE_VISIBILITY is set in the affirmative.
> In my humble opinion, it would be a good idea to add a "-werror" to the test 
> in visibility.m4 so that it won't set CFLAGS_VISIBILITY and HAVE_VISIBILITY 
> on those platforms that don't actually support it.
> What do you think?

I agree, and I recall that this was also suggested earlier.  The current
approach leads to one warning per compiled source file, which is rather

Bruno, how about this patch?


diff --git a/m4/visibility.m4 b/m4/visibility.m4
index 35a6dc0..06537d6 100644
--- a/m4/visibility.m4
+++ b/m4/visibility.m4
@@ -29,7 +29,11 @@ AC_DEFUN([gl_VISIBILITY],
     AC_MSG_CHECKING([for simple visibility declarations])
     AC_CACHE_VAL([gl_cv_cc_visibility], [
-      CFLAGS="$CFLAGS -fvisibility=hidden"
+      # We use -Werror here because Cygwin/MinGW gives a warning
+      # 'visibility attribute not supported in this configuration'
+      # instead of doing what we want.  Using -Werror makes gcc fail
+      # instead, so we detect the problem.
+      CFLAGS="$CFLAGS -fvisibility=hidden -Werror"
         [extern __attribute__((__visibility__("hidden"))) int hiddenvar;
          extern __attribute__((__visibility__("default"))) int exportedvar;

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