diff mbox

fork in libpthread cannot use IFUNC resolver [BZ #19861]

Message ID 20160524091019.269A04222879F@oldenburg.str.redhat.com
State New
Headers show

Commit Message

Florian Weimer May 24, 2016, 9:10 a.m. UTC 
The __libc_fork symbol may not have been relocated when the
resolver runs.  This commit only addresses the fork case,
the vfork case has to be a tail call, which is why the generic
code needs an IFUNC resolver there.

2016-05-24  Florian Weimer  <fweimer@redhat.com>

	[BZ #19861]
	Do not use IFUNC resolver with potentially unrelcated symbol.
	* nptl/pt-fork.c [HAVE_IFUNC]: Remove.

Comments

Roland McGrath May 27, 2016, 7:51 p.m. UTC | #1 
> 	[BZ #19861]
> 	Do not use IFUNC resolver with potentially unrelcated symbol.

typo: "unrelocated"

> --- a/nptl/pt-fork.c
> +++ b/nptl/pt-fork.c
> @@ -25,48 +25,20 @@
>     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.  */
> +   libpthread.so.  */

I think it's worthwhile for this comment to address the IFUNC issue.
e.g., "It's tempting to avoid the tail-call overhead in the shared library
case by using IFUNC here, but ..."

> -DEFINE_FORK (fork_ifunc)
> +strong_alias (fork_compat, fork_ifunc)
>  compat_symbol (libpthread, fork_ifunc, fork, GLIBC_2_0);
>  
> -DEFINE_FORK (__fork_ifunc)
> +strong_alias (fork_compat, __fork_ifunc)
>  compat_symbol (libpthread, __fork_ifunc, __fork, GLIBC_2_0);

Nothing that remains should have "ifunc" in the name.


Thanks,
Roland
diff mbox

Patch

diff --git a/nptl/pt-fork.c b/nptl/pt-fork.c
index b65d6b4..9773dc4 100644
--- a/nptl/pt-fork.c
+++ b/nptl/pt-fork.c
@@ -25,48 +25,20 @@ 
    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.  */
+   libpthread.so.  */
 
 #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 ();
 }
 
-# define DEFINE_FORK(name) strong_alias (fork_compat, name)
-
-# endif  /* HAVE_IFUNC */
-
-DEFINE_FORK (fork_ifunc)
+strong_alias (fork_compat, fork_ifunc)
 compat_symbol (libpthread, fork_ifunc, fork, GLIBC_2_0);
 
-DEFINE_FORK (__fork_ifunc)
+strong_alias (fork_compat, __fork_ifunc)
 compat_symbol (libpthread, __fork_ifunc, __fork, GLIBC_2_0);
 
 #endif