[PATCH] lib: Use attribute symver when available to define symbol versioning.

[Mark Wielaard]

GCC 10 introduces a function attribute to define symbol versioning.
Add a configure check to see if __attribute__((symver)) is supported.
If it is then define the OLD_VERSION, NEW_VERSION, COMPAT_VERSION
and COMPAT_VERSION_NEWPROTO macros using just attribute symver,
attribute alias and typeof function names. And avoid defining symbols
in asm statements.

Signed-off-by: Mark Wielaard <mark@klomp.org>
---
 ChangeLog       |  4 ++++
 configure.ac    | 13 +++++++++++++
 lib/ChangeLog   |  5 +++++
 lib/eu-config.h | 20 ++++++++++++++++++--
 4 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 854568e0..bff3bdef 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2020-04-10  Mark Wielaard  <mark@klomp.org>
+
+	* configure.ac: Add __attribute__((symver)) check.
+
 2020-03-30  Mark Wielaard  <mark@klomp.org>
 
 	* configure.ac: Set version to 0.179.
diff --git a/configure.ac b/configure.ac
index a39e800f..2a0aaca8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -158,6 +158,19 @@ if test "$ac_cv_gcc_struct" = "yes"; then
 		  [Defined if __attribute__((gcc_struct)) is supported])
 fi
 
+AC_CACHE_CHECK([whether gcc supports __attribute__((symver))],
+	ac_cv_gcc_symver, [dnl
+save_CFLAGS="$CFLAGS"
+CFLAGS="$save_CFLAGS -Werror"
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([dnl
+__attribute__ ((__symver__ ("foo@VERS_1"))) int foo_v1 (void) { }
+])], ac_cv_gcc_symver=yes, ac_cv_gcc_symver=no)
+CFLAGS="$save_CFLAGS"])
+if test "$ac_cv_gcc_symver" = "yes"; then
+	AC_DEFINE([HAVE_GCC_SYMVER], [1],
+		  [Defined if __attribute__((symver)) is supported])
+fi
+
 AC_CACHE_CHECK([whether gcc supports -fPIC], ac_cv_fpic, [dnl
 save_CFLAGS="$CFLAGS"
 CFLAGS="$save_CFLAGS -fPIC -Werror"
diff --git a/lib/ChangeLog b/lib/ChangeLog
index 51c79841..07837cce 100644
--- a/lib/ChangeLog
+++ b/lib/ChangeLog
@@ -1,3 +1,8 @@
+2020-04-10  Mark Wielaard  <mark@klomp.org>
+
+	* eu-config.h: If HAVE_GCC_SYMVER define symbol versioning macros
+	using attribute symver.
+
 2019-08-25  Srđan Milaković  <sm108@rice.edu>
 
 	* dynamicsizehash_concurrent.{c,h}: New files.
diff --git a/lib/eu-config.h b/lib/eu-config.h
index 84b22d7c..ccbedeb0 100644
--- a/lib/eu-config.h
+++ b/lib/eu-config.h
@@ -177,6 +177,21 @@ asm (".section predict_data, \"aw\"; .previous\n"
 
 
 #ifdef SYMBOL_VERSIONING
+#ifdef HAVE_GCC_SYMVER
+# define OLD_VERSION(name, version) \
+  __attribute__((__symver__( #name "@" #version))) \
+  __attribute__((__alias__( #name ))) \
+  __typeof__( name ) _compat_##version_##name;
+#define NEW_VERSION(name, version) \
+  __attribute__((__symver__(#name "@@" #version))) \
+  __typeof__ ( name ) name ;
+# define COMPAT_VERSION_NEWPROTO(name, version, prefix) \
+  __attribute__((__symver__ ( #name "@" #version ))) \
+  __typeof__(_compat_##prefix##_##name) _compat_##prefix##_##name;
+# define COMPAT_VERSION(name, version, prefix) \
+  __attribute__((__symver__(#name "@" #version))) \
+  __typeof__(name) _compat_##prefix##_##name;
+#else /* HAVE_GCC_SYMVER */
 # define OLD_VERSION(name, version) \
   asm (".globl _compat." #version "." #name "\n" \
        "_compat." #version "." #name " = " #name "\n" \
@@ -190,13 +205,14 @@ asm (".section predict_data, \"aw\"; .previous\n"
 # define COMPAT_VERSION(name, version, prefix) \
   asm (".symver _compat." #version "." #name "," #name "@" #version); \
   __typeof (name) _compat_##prefix##_##name asm ("_compat." #version "." #name);
-#else
+#endif /* HAVE_GCC_SYMVER */
+#else /* SYMBOL_VERSIONING */
 # define OLD_VERSION(name, version) /* Nothing for static linking.  */
 # define NEW_VERSION(name, version) /* Nothing for static linking.  */
 # define COMPAT_VERSION_NEWPROTO(name, version, prefix) \
   error "should use #ifdef SYMBOL_VERSIONING"
 # define COMPAT_VERSION(name, version, prefix) error "should use #ifdef SYMBOL_VERSIONING"
-#endif
+#endif /* SYMBOL_VERSIONING */
 
 #ifndef FALLTHROUGH
 # ifdef HAVE_FALLTHROUGH
-- 
2.18.2