[COMMITTED,1/3] Clean up NPTL fork to be compat-only.
diff mbox

Message ID 20150206201843.AD5922C3A9B@topped-with-meat.com
State New
Headers show

Commit Message

Roland McGrath Feb. 6, 2015, 8:18 p.m. UTC
I don't know if there was a historical reason for libpthread to have a
fork wrapper, but there is certainly none in the current code.  This
change makes it compat-only.  It's similar to what I did for vfork,
but simpler for the no-IFUNC case since it doesn't matter whether the
tail call is proper or not.

Tested x86_64-linux-gnu.


Thanks,
Roland


	* nptl/pt-fork.c: Rewritten.  Put everything under
	[SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_22)].
	Use IFUNC to redirect when possible.
	* nptl/Versions (libpthread: GLIBC_2.22): New (empty) version set.

Comments

Rich Felker Feb. 7, 2015, 4:46 p.m. UTC | #1
On Fri, Feb 06, 2015 at 12:18:43PM -0800, Roland McGrath wrote:
> I don't know if there was a historical reason for libpthread to have a
> fork wrapper,

The historical reason was presumably that with libpthread, fork needs
to call pthread_atfork handlers, while the fork in libc (assuming libc
doesn't have pthread_atfork) could be a simple syscall wrapper.

Rich

Patch
diff mbox

--- a/nptl/Versions
+++ b/nptl/Versions
@@ -266,6 +266,9 @@  libpthread {
   GLIBC_2.20 {
   }
 
+  GLIBC_2.22 {
+  }
+
   GLIBC_PRIVATE {
     __pthread_initialize_minimal;
     __pthread_clock_gettime; __pthread_clock_settime;
--- a/nptl/pt-fork.c
+++ b/nptl/pt-fork.c
@@ -1,4 +1,5 @@ 
-/* Copyright (C) 2002-2015 Free Software Foundation, Inc.
+/* ABI compatibility for 'fork' symbol in libpthread ABI.
+   Copyright (C) 2002-2015 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
 
@@ -17,11 +18,55 @@ 
    <http://www.gnu.org/licenses/>.  */
 
 #include <unistd.h>
+#include <shlib-compat.h>
 
+/* libpthread once had its own fork, though there was no apparent reason
+   for it.  There is no use in having a separate symbol in libpthread, but
+   the historical ABI requires it.  For static linking, there is no need to
+   provide anything here--the libc version will be linked in.  For shared
+   library ABI compatibility, there must be __fork and fork symbols in
+   libpthread.so; so we define them using IFUNC to redirect to the libc
+   function.  */
 
-pid_t
-__fork (void)
+#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_22)
+
+# if HAVE_IFUNC
+
+static __typeof (fork) *
+__attribute__ ((used))
+fork_resolve (void)
+{
+  return &__libc_fork;
+}
+
+#  ifdef HAVE_ASM_SET_DIRECTIVE
+#   define DEFINE_FORK(name) \
+  asm (".set " #name ", fork_resolve\n" \
+       ".globl " #name "\n" \
+       ".type " #name ", %gnu_indirect_function");
+#  else
+#   define DEFINE_FORK(name) \
+  asm (#name " = fork_resolve\n" \
+       ".globl " #name "\n" \
+       ".type " #name ", %gnu_indirect_function");
+#  endif
+
+# else  /* !HAVE_IFUNC */
+
+static pid_t __attribute__ ((used))
+fork_compat (void)
 {
   return __libc_fork ();
 }
-strong_alias (__fork, fork)
+
+# define DEFINE_FORK(name) strong_alias (fork_compat, name)
+
+# endif  /* HAVE_IFUNC */
+
+DEFINE_FORK (fork_ifunc)
+compat_symbol (libpthread, fork_ifunc, fork, GLIBC_2_0);
+
+DEFINE_FORK (__fork_ifunc)
+compat_symbol (libpthread, __fork_ifunc, __fork, GLIBC_2_0);
+
+#endif