On a zEC12 or z13, a glibc with lock elision enabled infers from HWCAP
that the prerequisites for lock elision are met.  Then it may use TBEGIN
and other transactional-execution instructions which are not implemented
by Valgrind.  Likewise, the upcoming glibc 2.23 will exploit vector
instructions if they are advertised by HWCAP; and those are currently
not implemented by Valgrind either.  In general, the increased use of
ifunc may lead to more such cases in the future.

This patch suppresses the advertising of those hardware features via
HWCAP which are either not known to Valgrind or currently unsupported.

Patch by Andreas Arnez (arnez@linux.vnet.ibm.com).
Fixes BZ #353680.

Modified: trunk/README.s390
==============================================================================
--- trunk/README.s390 (original)
+++ trunk/README.s390 Mon Oct 12 21:35:56 2015
@@ -22,6 +22,9 @@
 - Some gcc versions use mvc to copy 4/8 byte values. This will affect
   certain debug messages. For example, memcheck will complain about
   4 one-byte reads/writes instead of just a single read/write.
+- The transactional-execution facility is not supported; it is masked
+  off from HWCAP.
+- The vector facility is not supported; it is masked off from HWCAP.
 
 
 Hardware facilities

Modified: trunk/coregrind/m_initimg/initimg-linux.c
==============================================================================
--- trunk/coregrind/m_initimg/initimg-linux.c (original)
+++ trunk/coregrind/m_initimg/initimg-linux.c Mon Oct 12 21:35:56 2015
@@ -701,6 +701,12 @@
                  in syswrap-arm-linux.c rather than to base this on
                  conditional compilation. */
             }
+#           elif defined(VGP_s390x_linux)
+            {
+               /* Advertise hardware features "below" TE only.  TE and VXRS
+                  (and anything above) are not supported by Valgrind. */
+               auxv->u.a_val &= VKI_HWCAP_S390_TE - 1;
+            }
 #           endif
             break;
 #        if defined(VGP_ppc64be_linux) || defined(VGP_ppc64le_linux)

Modified: trunk/include/vki/vki-s390x-linux.h
==============================================================================
--- trunk/include/vki/vki-s390x-linux.h (original)
+++ trunk/include/vki/vki-s390x-linux.h Mon Oct 12 21:35:56 2015
@@ -800,12 +800,15 @@
 #define VKI_PTRACE_POKEUSR_AREA       0x5001
 
 //----------------------------------------------------------------------
-// From linux-2.6.16.60/include/asm-s390/elf.h
+// From linux-3.18/include/asm-s390/elf.h
 //----------------------------------------------------------------------
 
 typedef vki_s390_fp_regs vki_elf_fpregset_t;
 typedef vki_s390_regs vki_elf_gregset_t;
 
+#define VKI_HWCAP_S390_TE           1024
+#define VKI_HWCAP_S390_VXRS         2048
+
 
 //----------------------------------------------------------------------
 // From linux-2.6.16.60/include/asm-s390/ucontext.h