powerpc: Fix ifuncmain6pie failure with GCC 4.9

This patch fix the elf/ifuncmain6pie failure when building with GCC
4.9+.  For some reason, the compiler removes the branch taken code at
resolve_ifunc (sysdeps/powerpc/powerpc64/dl-machine.h) as dead-code
and thus the testcase fails because the ifunc resolves branches to an
invalid memory location.  It fixes by explicit adding a dependency of
value based on odp variable to avoid compiler optimization.

It fixes BZ#17868.

diff --git a/ChangeLog b/ChangeLog
index d746e18..cd09380 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2015-01-24  Adhemerval Zanellla  <azanella@linux.vnet.ibm.com>
+
+       [BZ #17868]
+       * sysdeps/powerpc/powerpc64/dl-machine.h (resolve_ifunc): Force value
+       set dependency from opd value.
+
 2015-01-23  H.J. Lu  <hongjiu.lu@intel.com>
 
        * sysdeps/x86_64/multiarch/init-arch.c (__init_cpu_features):

diff --git a/NEWS b/NEWS
index 0ce4352..f9ea7cf 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -18,7 +18,7 @@ Version 2.21
   17664, 17665, 17668, 17682, 17702, 17717, 17719, 17722, 17723, 17724,
   17725, 17732, 17733, 17744, 17745, 17746, 17747, 17748, 17775, 17777,
   17780, 17781, 17782, 17791, 17793, 17796, 17797, 17803, 17806, 17834,
-  17844, 17848, 17870
+  17844, 17848, 17868, 17870
 
 * A new semaphore algorithm has been implemented in generic C code for all
   machines. Previous custom assembly implementations of semaphore were

diff --git a/sysdeps/powerpc/powerpc64/dl-machine.h b/sysdeps/powerpc/powerpc64/dl-machine.h
index 9448712..47bb5a7 100644 (file)
--- a/sysdeps/powerpc/powerpc64/dl-machine.h
+++ b/sysdeps/powerpc/powerpc64/dl-machine.h
@@ -623,7 +623,9 @@ resolve_ifunc (Elf64_Addr value,
       opd.fd_func = func->fd_func + sym_map->l_addr;
       opd.fd_toc = func->fd_toc + sym_map->l_addr;
       opd.fd_aux = func->fd_aux;
-      value = (Elf64_Addr) &opd;
+      /* GCC 4.9+ eliminates the branch as dead code, force the odp set
+         dependency.  */
+      asm ("" : "=r" (value) : "0" (&opd), "X" (opd));
     }
 #endif
 #endif