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From "Martin Sebor (JIRA)" <j...@apache.org>
Subject [jira] Created: (STDCXX-1031) [gcc 4.1] make use of gcc 4.1 -fvisibility option
Date Wed, 04 Feb 2009 16:19:59 GMT
[gcc 4.1] make use of gcc 4.1 -fvisibility option
-------------------------------------------------

                 Key: STDCXX-1031
                 URL: https://issues.apache.org/jira/browse/STDCXX-1031
             Project: C++ Standard Library
          Issue Type: Improvement
          Components: Build and Installation
    Affects Versions: 4.2.1
         Environment: gcc 4.1 and better on ELF targets
            Reporter: Martin Sebor
            Assignee: Martin Sebor
             Fix For: 4.2.2


The gcc 4.1 {{[-fvisibility | http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Code-Gen-Options.html#index-fvisibility-1636]}}
option is said to
{quote}
??...very substantially improve linking and load times of shared object libraries, produce
more optimized code, provide near-perfect API export and prevent symbol clashes. It is *strongly*
recommended that you use this in any shared objects you distribute.??
{quote}

In order for stdcxx users to benefit as described in the gcc manual we should make use of
the {{-fvisibility=hidden}} option in conjunction with {{[\_\_attribute\_\_((visibility("default")))
| http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Function-Attributes.html#index-g_t_0040code_007bvisibility_007d-attribute-1830]}}
on exported interfaces as the gcc manual recommends.

Besides adding the {{-fvisibility=hidden}} option to the command line when building shared
libraries with gcc, the implementation involves defining the {{_RWSTD_EXPORT}} macro for gcc
as follows:
{code}
#define _RWSTD_EXPORT __attribute__ ((visibility ("default")))
{code}

Note that since gcc requires the {{\_\_attribute\_\_}} decoration only on function declarations
and issues a warning when it appears on definitions so the {{_RWSTD_EXPORT}} macro must not
be used on definitions.

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