[gem5-dev] changeset in gem5: syscall emulation: fix DPRINTF arg ordering bug

[Steve Reinhardt via gem5-dev]

changeset 00086092d9f7 in /z/repo/gem5
details: http://repo.gem5.org/gem5?cmd=changeset;node=00086092d9f7
description:
        syscall emulation: fix DPRINTF arg ordering bug

        When we switched getSyscallArg() from explicit arg indices to
        the implicit method, some DPRINTF arguments were left as calls
        to getSyscallArg(), even though C/C++ doesn't guarantee
        anything about the order of invocation of these calls.  As a
        result, the args could be printed out in arbitrary orders.

        Interestingly, this bug has been around since 2009:
        http://repo.gem5.org/gem5/rev/4842482e1bd1

diffstat:

 src/sim/syscall_emul.cc |  31 +++++++++++++++++--------------
 1 files changed, 17 insertions(+), 14 deletions(-)

diffs (55 lines):

diff -r c625a3c51bac -r 00086092d9f7 src/sim/syscall_emul.cc
--- a/src/sim/syscall_emul.cc   Wed Jul 09 09:28:15 2014 -0400
+++ b/src/sim/syscall_emul.cc   Fri Jul 18 22:05:51 2014 -0700
@@ -55,16 +55,19 @@
 void
 SyscallDesc::doSyscall(int callnum, LiveProcess *process, ThreadContext *tc)
 {
-#if TRACING_ON
-    int index = 0;
-#endif
-    DPRINTFR(SyscallVerbose,
-             "%d: %s: syscall %s called w/arguments %d,%d,%d,%d\n",
-             curTick(), tc->getCpuPtr()->name(), name,
-             process->getSyscallArg(tc, index),
-             process->getSyscallArg(tc, index),
-             process->getSyscallArg(tc, index),
-             process->getSyscallArg(tc, index));
+    if (DTRACE(SyscallVerbose)) {
+        int index = 0;
+        IntReg arg[4];
+
+        // we can't just put the calls to getSyscallArg() in the
+        // DPRINTF arg list, because C++ doesn't guarantee their order
+        for (int i = 0; i < 4; ++i)
+            arg[i] = process->getSyscallArg(tc, index);
+
+        DPRINTFNR("%d: %s: syscall %s called w/arguments %d,%d,%d,%d\n",
+                  curTick(), tc->getCpuPtr()->name(), name,
+                  arg[0], arg[1], arg[2], arg[3]);
+    }
 
     SyscallReturn retval = (*funcPtr)(this, callnum, process, tc);
 
@@ -91,8 +94,8 @@
            ThreadContext *tc)
 {
     int index = 0;
-    warn("ignoring syscall %s(%d, %d, ...)", desc->name,
-         process->getSyscallArg(tc, index), process->getSyscallArg(tc, index));
+    warn("ignoring syscall %s(%d, ...)", desc->name,
+         process->getSyscallArg(tc, index));
 
     return 0;
 }
@@ -103,8 +106,8 @@
            ThreadContext *tc)
 {
     int index = 0;
-    warn_once("ignoring syscall %s(%d, %d, ...)", desc->name,
-         process->getSyscallArg(tc, index), process->getSyscallArg(tc, index));
+    warn_once("ignoring syscall %s(%d, ...)", desc->name,
+              process->getSyscallArg(tc, index));
 
     return 0;
 }
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