[PATCH] nptl: Open libgcc.so with RTLD_NOW during pthread_cancel

[Florian Weimer]

Disabling lazy binding reduces stack usage during unwinding.

Note that RTLD_NOW only makes a difference if libgcc.so has not
already been loaded, so this is only a partial fix.

2018-01-10  Florian Weimer  <fweimer@redhat.com>

	[BZ #22636]
	* sysdeps/nptl/unwind-forcedunwind.c (pthread_cancel_init): Open
	libgcc.so with RTLD_NOW, to avoid lazy binding during unwind.

diff --git a/sysdeps/nptl/unwind-forcedunwind.c b/sysdeps/nptl/unwind-forcedunwind.c
index ab4350de99..67b8e74b53 100644
--- a/sysdeps/nptl/unwind-forcedunwind.c
+++ b/sysdeps/nptl/unwind-forcedunwind.c
@@ -49,7 +49,7 @@ pthread_cancel_init (void)
       return;
     }
 
-  handle = __libc_dlopen (LIBGCC_S_SO);
+  handle = __libc_dlopen_mode (LIBGCC_S_SO, RTLD_NOW | __RTLD_DLOPEN);
 
   if (handle == NULL
       || (resume = __libc_dlsym (handle, "_Unwind_Resume")) == NULL