[PATCH] Add support for referencing specific symbol versions

[fweimer at redhat dot com (Florian Weimer)]

This is needed for writing tests of compat symbols.

2016-06-22  Florian Weimer  <fweimer@redhat.com>

	Support linking against compatibility symbols, for use in tests.
	* include/libc-symbols.h (symbol_version_reference): New macro.
	(symbol_version): Use it.
	* include/shlib-compat.h: Unconditionally include <abi-versions.h>.
	(compat_symbol): Use compat_symbol_reference.
	(compat_symbol_1, compat_symbol_2): Remove.
	(compat_symbol_reference, compat_symbol_reference_1)
	(compat_symbol_reference_2): New macro.  Use
	symbol_version_reference.

diff --git a/include/libc-symbols.h b/include/libc-symbols.h
index 4548e09..c2b499a 100644
--- a/include/libc-symbols.h
+++ b/include/libc-symbols.h
@@ -282,19 +282,28 @@ for linking")
    past the last element in SET.  */
 #define symbol_set_end_p(set, ptr) ((ptr) >= (void *const *) &__stop_##set)
 
+/* Use symbol_version_reference to specify the version a symbol
+   reference should link to.  Use symbol_version or
+   default_symbol_version for the definition of a versioned symbol.
+   The difference is that the latter is a no-op in non-shared
+   builds.  */
+#ifdef __ASSEMBLER__
+# define symbol_version_reference(real, name, version) \
+     .symver real, name##@##version
+#else  /* !__ASSEMBLER__ */
+# define symbol_version_reference(real, name, version) \
+  __asm__ (".symver " #real "," #name "@" #version)
+#endif
+
 #ifdef SHARED
 # define symbol_version(real, name, version) \
-     _symbol_version(real, name, version)
+  symbol_version_reference(real, name, version)
 # define default_symbol_version(real, name, version) \
      _default_symbol_version(real, name, version)
 # ifdef __ASSEMBLER__
-#  define _symbol_version(real, name, version) \
-     .symver real, name##@##version
 #  define _default_symbol_version(real, name, version) \
      .symver real, name##@##@##version
 # else
-#  define _symbol_version(real, name, version) \
-     __asm__ (".symver " #real "," #name "@" #version)
 #  define _default_symbol_version(real, name, version) \
      __asm__ (".symver " #real "," #name "@@" #version)
 # endif
diff --git a/include/shlib-compat.h b/include/shlib-compat.h
index c1c5e2c..025c731 100644
--- a/include/shlib-compat.h
+++ b/include/shlib-compat.h
@@ -19,10 +19,10 @@
 #ifndef _SHLIB_COMPAT_H
 #define _SHLIB_COMPAT_H	1
 
-#ifdef SHARED
-
 # include <abi-versions.h>
 
+#ifdef SHARED
+
 /* The file abi-versions.h (generated by scripts/abi-versions.awk) defines
    symbols like `ABI_libm_GLIBC_2_0' for each version set in the source
    code for each library.  For a version set that is subsumed by a later
@@ -62,11 +62,7 @@
   default_symbol_version (local, symbol, name)
 
 # define compat_symbol(lib, local, symbol, version) \
-  compat_symbol_1 (lib, local, symbol, version)
-# define compat_symbol_1(lib, local, symbol, version) \
-  compat_symbol_2 (local, symbol, VERSION_##lib##_##version)
-# define compat_symbol_2(local, symbol, name) \
-  symbol_version (local, symbol, name)
+  compat_symbol_reference (lib, local, symbol, version)
 
 #else
 
@@ -82,6 +78,14 @@
 
 #endif
 
+/* Use compat_symbol_reference for a reference to a specific version
+   of a symbol.  Use compat_symbol to define such a symbol.  */
+#define compat_symbol_reference(lib, local, symbol, version) \
+  compat_symbol_reference_1 (lib, local, symbol, version)
+#define compat_symbol_reference_1(lib, local, symbol, version) \
+  compat_symbol_reference_2 (local, symbol, VERSION_##lib##_##version)
+#define compat_symbol_reference_2(local, symbol, name) \
+  symbol_version_reference (local, symbol, name)
 
 # ifdef LINK_OBSOLETE_RPC
 /* Export the symbol for both static and dynamic linking.  */