From: Oliver Kurth <okurth@vmware.com>
Date: Fri, 15 Sep 2017 18:23:31 +0000 (-0700)
Subject: atomic asm snippets: Replace "memory" clobber with "Q" constraint
X-Git-Tag: stable-10.2.0~289
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=81fec44ea5303efa27fb0f04ba06f162ffdfb2df;p=thirdparty%2Fopen-vm-tools.git

atomic asm snippets: Replace "memory" clobber with "Q" constraint

In our atomic asm snippets, using the "Q" constraint,
(https://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html tells gcc
which exact memory is modified i.e. the bytes covered by the atomic variable),
is better than using the "memory" clobber (tells gcc that all memory is
modified, effectively a compiler memory barrier which prevents compiler
optimizations).
---

diff --git a/open-vm-tools/lib/include/vm_atomic.h b/open-vm-tools/lib/include/vm_atomic.h
index 45775938e..e089d0027 100644
--- a/open-vm-tools/lib/include/vm_atomic.h
+++ b/open-vm-tools/lib/include/vm_atomic.h
@@ -307,23 +307,24 @@ Atomic_ReadIfEqualWrite128(Atomic_uint128 *ptr,   // IN/OUT
    uint32 failed;
 
    LDST_LDST_MEM_BARRIER();
-   __asm__ __volatile__ (
-      "1: ldxp    %x0, %x1, [%3]      \n\t"
+   __asm__ __volatile__(
+      "1: ldxp    %x0, %x1, %3        \n\t"
       "   cmp     %x0, %x4            \n\t"
       "   ccmp    %x1, %x5, #0, eq    \n\t"
       "   b.ne    2f                  \n\t"
-      "   stxp    %w2, %x6, %x7, [%3] \n\t"
+      "   stxp    %w2, %x6, %x7, %3   \n\t"
       "   cbnz    %w2, 1b             \n\t"
       "2: clrex                       \n\t"
       : "=&r" (res.lo),
         "=&r" (res.hi),
-        "=&r" (failed)
-      : "r" (&ptr->value),
-        "r" (_old.lo),
+        "=&r" (failed),
+        "+Q" (ptr->value)
+      : "r" (_old.lo),
         "r" (_old.hi),
         "r" (_new.lo),
         "r" (_new.hi)
-      : "cc", "memory");
+      : "cc"
+   );
    LDST_LDST_MEM_BARRIER();
 
    return res.raw;