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 ([email protected]).
Fixes BZ #353680.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@15702 a5019735-40e9-0310-863c-91ae7b9d1cf9

Author: florian

NEWS

@@ -35,6 +35,7 @@ where XXXXXX is the bug number as listed below.
 353084  arm64 doesn't support sigpending system call
 353370  don't advertise RDRAND in cpuid for Core-i7-4910-like avx2 machine
 353398  WARNING: unhandled amd64-solaris syscall: 207
+353680  s390x: Crash with certain glibc versions due to non-implemented TBEGIN
 
 
 

README.s390

@@ -22,6 +22,9 @@ Limitations
 - 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

coregrind/m_initimg/initimg-linux.c

@@ -701,6 +701,12 @@ Addr setup_client_stack( void*  init_sp,
                  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)

include/vki/vki-s390x-linux.h

@@ -800,12 +800,15 @@ typedef struct
 #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