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From: Bruno Haible <bruno@clisp.org>
To: Ozkan Sezer <sezeroz@gmail.com>
Cc: bug-gnulib@gnu.org
Subject: Re: [PATCH] make gl_VISIBILITY to reject unsupported configurations with newer gcc
Date: Sat, 05 Jun 2021 17:10:45 +0200	[thread overview]
Message-ID: <162293739.qyZAu42AHI@omega> (raw)
In-Reply-To: <CAA2C=vBUgzL8YA7HFkg2uTfpd_ezP6duvHx4c3ryJLeEOJ7Y=w@mail.gmail.com>

Ozkan Sezer wrote:
> >> The attached patch makes gl_VISIBILITY to reject unsupported configurations
> >> with newer gcc: In its current form, mingw gcc-4.5.4 rejects the attributes
> >> but gcc-7.5 does not, apparently because the attributes are applied to func
> >> prototypes without their definitions.  Attaching a hidden visibility attrib
> >> to dummyfunc() makes gcc-7.5 to reject it properly.
> >
> > I don't fully understand why we should apply the patch.
> >
> > With gcc 7.5 on mingw and the visibility.m4 that is in gnulib now:
> > What is the result of the
> >   checking for simple visibility declarations...
> > test? What are the effects: warnings? compilation errors? link errors? too
> > many exported symbols? too few exported symbols?
> 
> No warnings from the testcase in m4. In real-life, it results in warnings,
> see e.g.: https://github.com/libsndfile/libsamplerate/issues/154

OK, I understand better now.

In the GCC source code I see that the
  "visibility attribute not supported in this configuration; ignored"
warning is emitted when a definition is emitted. Therefore I think the
safest patch is to add a definition for each declaration in the test code.


2021-06-05  Bruno Haible  <bruno@clisp.org>

	lib-symbol-visibility: Make configure check work for newer GCC.
	Reported by Ozkan Sezer <sezeroz@gmail.com> in
	<https://lists.gnu.org/archive/html/bug-gnulib/2021-05/msg00117.html>.
	* m4/visibility.m4 (gl_VISIBILITY): Add a function definition for each
	declaration in the test program.

diff --git a/m4/visibility.m4 b/m4/visibility.m4
index 8f27a12..d161bd7 100644
--- a/m4/visibility.m4
+++ b/m4/visibility.m4
@@ -1,4 +1,4 @@
-# visibility.m4 serial 7
+# visibility.m4 serial 8
 dnl Copyright (C) 2005, 2008, 2010-2021 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -59,6 +59,10 @@ AC_DEFUN([gl_VISIBILITY],
               extern __attribute__((__visibility__("hidden"))) int hiddenfunc (void);
               extern __attribute__((__visibility__("default"))) int exportedfunc (void);
               void dummyfunc (void);
+              int hiddenvar;
+              int exportedvar;
+              int hiddenfunc (void) { return 51; }
+              int exportedfunc (void) { return 1225736919; }
               void dummyfunc (void) {}
             ]],
             [[]])],



  reply	other threads:[~2021-06-05 15:10 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-25 15:54 [PATCH] make gl_VISIBILITY to reject unsupported configurations with newer gcc Ozkan Sezer
2021-05-25 23:54 ` Bruno Haible
2021-05-26  0:34   ` Ozkan Sezer
2021-06-05 15:10     ` Bruno Haible [this message]
2021-06-05 16:21       ` Ozkan Sezer

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