Commit 7d214f4d authored by Simon McVittie's avatar Simon McVittie

On Unix platforms with gcc (or compatible), hide non-exported symbols

This changes the Linux behaviour to match the default situation
on Windows: symbols without DBUS_EXPORT or DBUS_PRIVATE_EXPORT
decoration are internal to libdbus-1, and cannot be used by
other programs, even within the dbus source tree.

This means the compiler/linker can optimize calls to those functions
by avoiding indirection through the PLT, which should improve
performance a little. However, the primary purpose of doing this is
that it means developers building libdbus on Linux are considerably
less likely to break it on Windows by mistake.

I'm deliberately not adding -fvisbility=hidden in CMake because the
complexity of doing so is unnecessary: Autotools is the recommended
way to build dbus for Unix, and the one Unix developers are going
to use in practice, unless they are specifically checking that they
haven't broken the CMake build.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=83115Reviewed-by: Ralf Habacker's avatarRalf Habacker <ralf.habacker@freenet.de>
parent 6bcf34d4
......@@ -71,6 +71,11 @@ COMPILER_COVERAGE
COMPILER_OPTIMISATIONS
PKG_PROG_PKG_CONFIG
# This must come before we set up compiler warnings because it assumes
# non-use of -Werror=missing-prototypes
gl_VISIBILITY
AM_CONDITIONAL([HAVE_VISIBILITY], [test "x$HAVE_VISIBILITY" = x1])
# Initialize libtool
LT_INIT([win32-dll])
LT_LANG([Windows Resource])
......
......@@ -12,6 +12,18 @@ AM_CPPFLAGS = \
-DDBUS_SESSION_CONFIG_FILE=\""$(configdir)/session.conf"\" \
$(NULL)
AM_CFLAGS =
if HAVE_VISIBILITY
if !DBUS_WIN
AM_CFLAGS += $(CFLAG_VISIBILITY)
AM_CPPFLAGS += \
-DDBUS_EXPORT='__attribute__((__visibility__("default")))' \
-DDBUS_PRIVATE_EXPORT='__attribute__((__visibility__("default")))' \
$(NULL)
endif
endif
# if assertions are enabled, improve backtraces
AM_LDFLAGS = @R_DYNAMIC_LDFLAG@
......
# visibility.m4 serial 5 (gettext-0.18.2)
dnl Copyright (C) 2005, 2008, 2010-2014 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.
dnl From Bruno Haible.
dnl Tests whether the compiler supports the command-line option
dnl -fvisibility=hidden and the function and variable attributes
dnl __attribute__((__visibility__("hidden"))) and
dnl __attribute__((__visibility__("default"))).
dnl Does *not* test for __visibility__("protected") - which has tricky
dnl semantics (see the 'vismain' test in glibc) and does not exist e.g. on
dnl Mac OS X.
dnl Does *not* test for __visibility__("internal") - which has processor
dnl dependent semantics.
dnl Does *not* test for #pragma GCC visibility push(hidden) - which is
dnl "really only recommended for legacy code".
dnl Set the variable CFLAG_VISIBILITY.
dnl Defines and sets the variable HAVE_VISIBILITY.
AC_DEFUN([gl_VISIBILITY],
[
AC_REQUIRE([AC_PROG_CC])
CFLAG_VISIBILITY=
HAVE_VISIBILITY=0
if test -n "$GCC"; then
dnl First, check whether -Werror can be added to the command line, or
dnl whether it leads to an error because of some other option that the
dnl user has put into $CC $CFLAGS $CPPFLAGS.
AC_MSG_CHECKING([whether the -Werror option is usable])
AC_CACHE_VAL([gl_cv_cc_vis_werror], [
gl_save_CFLAGS="$CFLAGS"
CFLAGS="$CFLAGS -Werror"
AC_COMPILE_IFELSE(
[AC_LANG_PROGRAM([[]], [[]])],
[gl_cv_cc_vis_werror=yes],
[gl_cv_cc_vis_werror=no])
CFLAGS="$gl_save_CFLAGS"])
AC_MSG_RESULT([$gl_cv_cc_vis_werror])
dnl Now check whether visibility declarations are supported.
AC_MSG_CHECKING([for simple visibility declarations])
AC_CACHE_VAL([gl_cv_cc_visibility], [
gl_save_CFLAGS="$CFLAGS"
CFLAGS="$CFLAGS -fvisibility=hidden"
dnl We use the option -Werror and a function dummyfunc, because on some
dnl platforms (Cygwin 1.7) the use of -fvisibility triggers a warning
dnl "visibility attribute not supported in this configuration; ignored"
dnl at the first function definition in every compilation unit, and we
dnl don't want to use the option in this case.
if test $gl_cv_cc_vis_werror = yes; then
CFLAGS="$CFLAGS -Werror"
fi
AC_COMPILE_IFELSE(
[AC_LANG_PROGRAM(
[[extern __attribute__((__visibility__("hidden"))) int hiddenvar;
extern __attribute__((__visibility__("default"))) int exportedvar;
extern __attribute__((__visibility__("hidden"))) int hiddenfunc (void);
extern __attribute__((__visibility__("default"))) int exportedfunc (void);
void dummyfunc (void) {}
]],
[[]])],
[gl_cv_cc_visibility=yes],
[gl_cv_cc_visibility=no])
CFLAGS="$gl_save_CFLAGS"])
AC_MSG_RESULT([$gl_cv_cc_visibility])
if test $gl_cv_cc_visibility = yes; then
CFLAG_VISIBILITY="-fvisibility=hidden"
HAVE_VISIBILITY=1
fi
fi
AC_SUBST([CFLAG_VISIBILITY])
AC_SUBST([HAVE_VISIBILITY])
AC_DEFINE_UNQUOTED([HAVE_VISIBILITY], [$HAVE_VISIBILITY],
[Define to 1 or 0, depending whether the compiler supports simple visibility declarations.])
])
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