Support for multiple versions in versioned_symbol, compat_symbol

This essentially folds compat_symbol_unique functionality into
compat_symbol.

This change eliminates the need for intermediate aliases for defining
multiple symbol versions, for both compat_symbol and versioned_symbol.
Some binutils versions do not suport multiple versions per symbol on
some targets, so aliases are automatically introduced, similar to what
compat_symbol_unique did.  To reduce symbol table sizes, a configure
check is added to avoid these aliases if they are not needed.

The new mechanism works with data symbols as well as function symbols,
due to the way an assembler-level redirect is used.  It is not
compatible with weak symbols for old binutils versions, which is why
the definition of __malloc_initialize_hook had to be changed.  This
is not a loss of functionality because weak symbols do not matter
to dynamic linking.

The placeholder symbol needs repeating in nptl/libpthread-compat.c
now that compat_symbol is used, but that seems more obvious than
introducing yet another macro.

A subtle difference was that compat_symbol_unique made the symbol
global automatically.  compat_symbol does not do this, so static
had to be removed from the definition of
__libpthread_version_placeholder.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

config.h.in

@@ -190,6 +190,10 @@
 /* Define if the linker defines __ehdr_start.  */
 #undef HAVE_EHDR_START
 
+/* Define to 1 if the assembler needs intermediate aliases to define
+   multiple symbol versions for one symbol.  */
+#define SYMVER_NEEDS_ALIAS 0
+
 /*
  */
 

configure

@@ -6590,6 +6590,34 @@ elif test "$libc_cv_ehdr_start" = broken; then
 $as_echo "$as_me: WARNING: linker is broken -- you should upgrade" >&2;}
 fi
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the assembler requires one version per symbol" >&5
+$as_echo_n "checking whether the assembler requires one version per symbol... " >&6; }
+if ${libc_cv_symver_needs_alias+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+    cat > conftest.s <<EOF
+        .text
+testfunc:
+        .globl testfunc
+        .symver testfunc, testfunc1@VERSION1
+        .symver testfunc, testfunc1@VERSION2
+EOF
+  libc_cv_symver_needs_alias=no
+  if ${CC-cc} $ASFLAGS -c conftest.s 2>&5; then
+    libc_cv_symver_needs_alias=no
+  else
+    libc_cv_symver_needs_alias=yes
+  fi
+  rm conftest.*
+
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_symver_needs_alias" >&5
+$as_echo "$libc_cv_symver_needs_alias" >&6; }
+if test "$libc_cv_symver_needs_alias" = yes; then
+  $as_echo "#define SYMVER_NEEDS_ALIAS 1" >>confdefs.h
+
+fi
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for __builtin_trap with no external dependencies" >&5
 $as_echo_n "checking for __builtin_trap with no external dependencies... " >&6; }
 if ${libc_cv_builtin_trap+:} false; then :

configure.ac

@@ -1673,6 +1673,29 @@ elif test "$libc_cv_ehdr_start" = broken; then
   AC_MSG_WARN([linker is broken -- you should upgrade])
 fi
 
+dnl Starting with binutils 2.35, GAS can attach multiple symbol versions
+dnl to one symbol (PR 23840).
+AC_CACHE_CHECK(whether the assembler requires one version per symbol,
+               libc_cv_symver_needs_alias, [dnl
+  cat > conftest.s <<EOF
+        .text
+testfunc:
+        .globl testfunc
+        .symver testfunc, testfunc1@VERSION1
+        .symver testfunc, testfunc1@VERSION2
+EOF
+  libc_cv_symver_needs_alias=no
+  if ${CC-cc} $ASFLAGS -c conftest.s 2>&AS_MESSAGE_LOG_FD; then
+    libc_cv_symver_needs_alias=no
+  else
+    libc_cv_symver_needs_alias=yes
+  fi
+  rm conftest.*
+])
+if test "$libc_cv_symver_needs_alias" = yes; then
+  AC_DEFINE(SYMVER_NEEDS_ALIAS)
+fi
+
 AC_CACHE_CHECK(for __builtin_trap with no external dependencies,
 	       libc_cv_builtin_trap, [dnl
 libc_cv_builtin_trap=no

include/libc-symbols.h

@@ -404,12 +404,13 @@ for linking")
   symbol_version_reference(real, name, version)
 # define default_symbol_version(real, name, version) \
      _default_symbol_version(real, name, version)
+/* See <libc-symver.h>.  */
 # ifdef __ASSEMBLER__
 #  define _default_symbol_version(real, name, version) \
-     .symver real, name##@##@##version
+  _set_symbol_version (real, name@@version)
 # else
 #  define _default_symbol_version(real, name, version) \
-     __asm__ (".symver " #real "," #name "@@" #version)
+  _set_symbol_version (real, #name "@@" #version)
 # endif
 
 /* Evalutes to a string literal for VERSION in LIB.  */

include/shlib-compat.h

@@ -62,6 +62,20 @@
    i.e. either GLIBC_2.1 or the "earliest version" specified in
    shlib-versions if that is newer.  */
 
+/* versioned_symbol (LIB, LOCAL, SYMBOL, VERSION) emits a definition
+   of SYMBOL with a default (@@) VERSION appropriate for LIB.  (The
+   actually emitted symbol version is adjusted according to the
+   baseline symbol version for LIB.)  The address of the symbol is
+   taken from LOCAL.  Properties of LOCAL are copied to the exported
+   symbol.  In particular, LOCAL itself should be global.  It is
+   unspecified whether SYMBOL@VERSION is associated with LOCAL, or if
+   an intermediate alias is created.  If LOCAL and SYMBOL are
+   distinct, and LOCAL is also intended for export, its version should
+   be specified explicitly with versioned_symbol, too.
+
+   If LOCAL is a data symbol and does not have a non-zero initializer,
+   it should be defined with __attribute__ ((nocommon)) for
+   compatibility with GCC versions that default to -fcommon.  */
 # define versioned_symbol(lib, local, symbol, version) \
   versioned_symbol_1 (lib, local, symbol, version)
 # define versioned_symbol_1(lib, local, symbol, version) \
@@ -69,44 +83,25 @@
 # define versioned_symbol_2(local, symbol, name) \
   default_symbol_version (local, symbol, name)
 
+/* compat_symbol is like versioned_symbol, but emits a compatibility
+   version (with @ instead of @@).  The same issue related to
+   intermediate aliases applies, so LOCAL should not be listed in the
+   Versions file, or otherwise it can be exported with an undesired
+   default symbol version.  */
 # define compat_symbol(lib, local, symbol, version) \
-  compat_symbol_reference (lib, local, symbol, version)
-
-/* This is similar to compat_symbol, but allows versioning the same symbol
-   to multiple version without having multiple symbol definitions.  For
-   instance:
-
-   #if (SHLIB_COMPAT (libpthread, GLIBC_2_1_2, GLIBC_2_2))
-   compat_symbol_unique (libc, old_foo, GLIBC_2_1_2)
-   #endif
-
-   #if (SHLIB_COMPAT (libpthread, GLIBC_2_2_6, GLIBC_2_3))
-   compat_symbol_unique (libc, old_foo, GLIBC_2_2_6)
-   #endif
-
-   Internally it creates a unique strong alias to the input symbol and
-   creates one compat_symbol on the alias.  Using the above example,
-   it is similar to:
-
-   #if (SHLIB_COMPAT (libpthread, GLIBC_2_1_2, GLIBC_2_2))
-   strong_alias (old_foo, old_foo__COUNTER__)
-   compat_symbol (libc, old_foo__COUNTER__, foo, GLIBC_2_2)
-   #endif.
-
-   With __COUNTER__ being a monotonic number generated by the compiler.  */
-
-# define __compat_symbol_unique_concat(x, y) x ## y
-# define _compat_symbol_unique_concat(x, y) \
-  __compat_symbol_unique_concat (x, y)
-# define _compat_symbol_unique_alias(name) \
-  _compat_symbol_unique_concat (name, __COUNTER__)
-# define _compat_symbol_unique(lib, orig_name, name, version) \
-  strong_alias (orig_name, name) \
-  compat_symbol (lib, name, orig_name, version)
-# define compat_symbol_unique(lib, name, version) \
-  _compat_symbol_unique (lib, name, _compat_symbol_unique_alias (name), \
-                         version)
-
+  compat_symbol_1 (lib, local, symbol, version)
+# define compat_symbol_1(lib, local, symbol, version) \
+  compat_symbol_2 (local, symbol, VERSION_##lib##_##version)
+/* See <libc-symver.h>.  */
+# ifdef __ASSEMBLER__
+#define compat_symbol_2(local, symbol, name) \
+  _set_symbol_version (local, symbol@name)
+# else
+#  define compat_symbol_2(local, symbol, name) \
+  compat_symbol_3 (local, symbol, name)
+#  define compat_symbol_3(local, symbol, name) \
+  _set_symbol_version (local, #symbol "@" #name)
+# endif
 #else
 
 /* Not compiling ELF shared libraries at all, so never any old versions.  */
@@ -118,16 +113,17 @@
 
 /* This should not appear outside `#if SHLIB_COMPAT (...)'.  */
 # define compat_symbol(lib, local, symbol, version) ...
-# define compat_symbol_unique(lib, name, version) ...
 
 #endif
 
 /* Use compat_symbol_reference for a reference *or* definition of a
-   specific version of a symbol.  Definitions are primarily used to
-   ensure tests reference the exact compat symbol required, or define an
-   interposing symbol of the right version e.g. __malloc_initialize_hook
-   in mcheck-init.c.  Use compat_symbol to define such a symbol within
-   the shared libraries that are built for users.  */
+   specific version of a symbol.  compat_symbol_reference does not
+   create intermediate aliases.  Definitions are primarily used to
+   ensure tests reference the exact compat symbol required, or define
+   an interposing symbol of the right version e.g.,
+   __malloc_initialize_hook in mcheck-init.c.  Use compat_symbol to
+   define such a symbol within the shared libraries that are built for
+   users.  */
 #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) \

malloc/malloc.c

@@ -1991,7 +1991,7 @@ static void *memalign_hook_ini (size_t alignment, size_t sz,
                                 const void *caller) __THROW;
 
 #if HAVE_MALLOC_INIT_HOOK
-void weak_variable (*__malloc_initialize_hook) (void) = NULL;
+void (*__malloc_initialize_hook) (void) __attribute__ ((nocommon));
 compat_symbol (libc, __malloc_initialize_hook,
 	       __malloc_initialize_hook, GLIBC_2_0);
 #endif

nptl/libpthread-compat.c

@@ -20,10 +20,10 @@
 #include <shlib-compat.h>
 
 #ifdef SHARED
-static void
+void
 attribute_compat_text_section
 __attribute_used__
-__libpthread_version_placeholder (void)
+__libpthread_version_placeholder_1 (void)
 {
 }
 #endif
@@ -37,16 +37,16 @@ __libpthread_version_placeholder (void)
    there are plenty of other symbols which populate those later
    versions.  */
 #if (SHLIB_COMPAT (libpthread, GLIBC_2_1_2, GLIBC_2_2))
-compat_symbol_unique (libpthread,
-		      __libpthread_version_placeholder, GLIBC_2_1_2);
+compat_symbol (libpthread, __libpthread_version_placeholder_1,
+	       __libpthread_version_placeholder, GLIBC_2_1_2);
 #endif
 
 #if (SHLIB_COMPAT (libpthread, GLIBC_2_2_3, GLIBC_2_2_4))
-compat_symbol_unique (libpthread,
-		      __libpthread_version_placeholder, GLIBC_2_2_3);
+compat_symbol (libpthread, __libpthread_version_placeholder_1,
+	       __libpthread_version_placeholder, GLIBC_2_2_3);
 #endif
 
 #if (SHLIB_COMPAT (libpthread, GLIBC_2_2_6, GLIBC_2_3))
-compat_symbol_unique (libpthread,
-		      __libpthread_version_placeholder, GLIBC_2_2_6);
+compat_symbol (libpthread, __libpthread_version_placeholder_1,
+	       __libpthread_version_placeholder, GLIBC_2_2_6);
 #endif

sysdeps/generic/libc-symver.h

@@ -22,17 +22,67 @@
 #ifndef _LIBC_SYMVER_H
 #define _LIBC_SYMVER_H 1
 
+#include <config.h>
+
 /* 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.  */
+   builds.
+
+   _set_symbol_version is similar to symbol_version_reference, except
+   that this macro expects the name and symbol version as a single
+   string or token sequence, with an @ or @@ separator.  (A string is
+   used in C mode and a token sequence in assembler mode.)
+   _set_symbol_version only be used for definitions because it may
+   introduce an alias symbol that would not be globally unique for
+   mere references.  The _set_symbol_version macro is used to define
+   default_symbol_version and compat_symbol.  */
+
 #ifdef __ASSEMBLER__
 # define symbol_version_reference(real, name, version) \
      .symver real, name##@##version
-#else  /* !__ASSEMBLER__ */
+#else
 # define symbol_version_reference(real, name, version) \
   __asm__ (".symver " #real "," #name "@" #version)
-#endif
+#endif  /* !__ASSEMBLER__ */
+
+#if SYMVER_NEEDS_ALIAS
+/* If the assembler cannot support multiple versions for the same
+   symbol, introduce __SInnn_ aliases to which the symbol version is
+   attached.  */
+# define __symbol_version_unique_concat(x, y) __SI ## x ## _ ## y
+# define _symbol_version_unique_concat(x, y) \
+  __symbol_version_unique_concat (x, y)
+# define _symbol_version_unique_alias(name) \
+  _symbol_version_unique_concat (name, __COUNTER__)
+# ifdef __ASSEMBLER__
+#  define _set_symbol_version_2(real, alias, name_version) \
+  .globl alias ASM_LINE_SEP                                \
+  .equiv alias, real ASM_LINE_SEP                          \
+  .symver alias, name_version
+# else
+#  define _set_symbol_version_2(real, alias, name_version) \
+  __asm__ (".globl " #alias "\n\t"                         \
+           ".equiv " #alias ", " #real "\n\t"              \
+           ".symver " #alias "," name_version)
+# endif
+# define _set_symbol_version_1(real, alias, name_version) \
+  _set_symbol_version_2 (real, alias, name_version)
+/* REAL must be globally unique, so that the counter also produces
+   globally unique symbols.  */
+# define _set_symbol_version(real, name_version)                   \
+  _set_symbol_version_1 (real, _symbol_version_unique_alias (real), \
+                               name_version)
+# else  /* !SYMVER_NEEDS_ALIAS */
+# ifdef __ASSEMBLER__
+#  define _set_symbol_version(real, name_version) \
+  .symver real, name_version
+# else
+#  define _set_symbol_version(real, name_version) \
+  __asm__ (".symver " #real "," name_version)
+# endif
+#endif  /* !SYMVER_NEEDS_ALIAS */
+
 
 #endif /* _LIBC_SYMVER_H */

sysdeps/ia64/libc-symver.h

@@ -0,0 +1,33 @@
+/* Symbol version management.  ia64 version.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _LIBC_SYMVER_H
+
+#include <sysdeps/generic/libc-symver.h>
+
+/* ia64 recognizes loc1 as a register name.  Add the # suffix to all
+   symbol references.  */
+#if !defined (__ASSEMBLER__) && SYMVER_NEEDS_ALIAS
+#undef _set_symbol_version_2
+# define _set_symbol_version_2(real, alias, name_version) \
+  __asm__ (".globl " #alias "#\n\t"                         \
+           ".equiv " #alias ", " #real "#\n\t"              \
+           ".symver " #alias "#," name_version)
+#endif
+
+#endif /* _LIBC_SYMVER_H */

time/clock_getcpuclockid.c

@@ -42,6 +42,5 @@ versioned_symbol (libc, __clock_getcpuclockid, clock_getcpuclockid, GLIBC_2_17);
 /* clock_getcpuclockid moved to libc in version 2.17;
    old binaries may expect the symbol version it had in librt.  */
 #if SHLIB_COMPAT (libc, GLIBC_2_2, GLIBC_2_17)
-strong_alias (__clock_getcpuclockid, __clock_getcpuclockid_2);
-compat_symbol (libc, __clock_getcpuclockid_2, clock_getcpuclockid, GLIBC_2_2);
+compat_symbol (libc, __clock_getcpuclockid, clock_getcpuclockid, GLIBC_2_2);
 #endif

time/clock_getres.c

@@ -32,8 +32,7 @@ versioned_symbol (libc, __clock_getres, clock_getres, GLIBC_2_17);
 /* clock_getres moved to libc in version 2.17;
    old binaries may expect the symbol version it had in librt.  */
 #if SHLIB_COMPAT (libc, GLIBC_2_2, GLIBC_2_17)
-strong_alias (__clock_getres, __clock_getres_2);
-compat_symbol (libc, __clock_getres_2, clock_getres, GLIBC_2_2);
+compat_symbol (libc, __clock_getres, clock_getres, GLIBC_2_2);
 #endif
 
 stub_warning (clock_getres)

time/clock_gettime.c

@@ -33,8 +33,7 @@ versioned_symbol (libc, __clock_gettime, clock_gettime, GLIBC_2_17);
 /* clock_gettime moved to libc in version 2.17;
    old binaries may expect the symbol version it had in librt.  */
 #if SHLIB_COMPAT (libc, GLIBC_2_2, GLIBC_2_17)
-strong_alias (__clock_gettime, __clock_gettime_2);
-compat_symbol (libc, __clock_gettime_2, clock_gettime, GLIBC_2_2);
+compat_symbol (libc, __clock_gettime, clock_gettime, GLIBC_2_2);
 #endif
 
 stub_warning (clock_gettime)

time/clock_nanosleep.c

@@ -38,8 +38,7 @@ versioned_symbol (libc, __clock_nanosleep, clock_nanosleep, GLIBC_2_17);
 /* clock_nanosleep moved to libc in version 2.17;
    old binaries may expect the symbol version it had in librt.  */
 #if SHLIB_COMPAT (libc, GLIBC_2_2, GLIBC_2_17)
-strong_alias (__clock_nanosleep, __clock_nanosleep_2);
-compat_symbol (libc, __clock_nanosleep_2, clock_nanosleep, GLIBC_2_2);
+compat_symbol (libc, __clock_nanosleep, clock_nanosleep, GLIBC_2_2);
 #endif
 
 stub_warning (clock_nanosleep)

time/clock_settime.c

@@ -33,8 +33,7 @@ versioned_symbol (libc, __clock_settime, clock_settime, GLIBC_2_17);
 /* clock_settime moved to libc in version 2.17;
    old binaries may expect the symbol version it had in librt.  */
 #if SHLIB_COMPAT (libc, GLIBC_2_2, GLIBC_2_17)
-strong_alias (__clock_settime, __clock_settime_2);
-compat_symbol (libc, __clock_settime_2, clock_settime, GLIBC_2_2);
+compat_symbol (libc, __clock_settime, clock_settime, GLIBC_2_2);
 #endif
 
 stub_warning (clock_settime)