[XRay] [compiler-rt] Include argv[0] in the log file name.

Summary:
If you decide to recompile parts of your Linux distro with XRay, it may
be useful to know which trace belongs to which binary.  While there, get
rid of the incorrect strncat() usage; it always returns a pointer to the
start which makes that if() always true.  Replace with snprintf which is
bounded so that enough from both strings fits nicely.

Reviewers: dberris

Subscribers: danalbert, srhines, kubabrecka, mgorny, llvm-commits

Differential Revision: https://reviews.llvm.org/D27912

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@290861 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 29 insertions, 6 deletions

diff --git a/lib/xray/xray_inmemory_log.cc b/lib/xray/xray_inmemory_log.cc
index 7ec56f486..adcb21671 100644
--- a/lib/xray/xray_inmemory_log.cc
+++ b/lib/xray/xray_inmemory_log.cc
@@ -112,14 +112,23 @@ static int __xray_OpenLogFile() XRAY_NEVER_INSTRUMENT {
   // Open a temporary file once for the log.
   static char TmpFilename[256] = {};
   static char TmpWildcardPattern[] = "XXXXXX";
-  auto E = internal_strncat(TmpFilename, flags()->xray_logfile_base,
-                            sizeof(TmpFilename) - 10);
-  if (static_cast<size_t>((E + 6) - TmpFilename) > (sizeof(TmpFilename) - 1)) {
-    Report("XRay log file base too long: %s\n", flags()->xray_logfile_base);
+  auto Argv = GetArgv();
+  const char *Progname = Argv[0] == nullptr ? "(unknown)" : Argv[0];
+  const char *LastSlash = internal_strrchr(Progname, '/');
+
+  if (LastSlash != nullptr)
+    Progname = LastSlash + 1;
+
+  const int HalfLength = sizeof(TmpFilename) / 2 - sizeof(TmpWildcardPattern);
+  int NeededLength = internal_snprintf(TmpFilename, sizeof(TmpFilename),
+                                       "%.*s%.*s.%s",
+                                       HalfLength, flags()->xray_logfile_base,
+                                       HalfLength, Progname,
+                                       TmpWildcardPattern);
+  if (NeededLength > int(sizeof(TmpFilename))) {
+    Report("XRay log file name too long (%d): %s\n", NeededLength, TmpFilename);
     return -1;
   }
-  internal_strncat(TmpFilename, TmpWildcardPattern,
-                   sizeof(TmpWildcardPattern) - 1);
   int Fd = mkstemp(TmpFilename);
   if (Fd == -1) {
     Report("XRay: Failed opening temporary file '%s'; not logging events.\n",
diff --git a/test/xray/TestCases/Linux/argv0-log-file-name.cc b/test/xray/TestCases/Linux/argv0-log-file-name.cc
new file mode 100644
index 000000000..1765ce9b5
--- /dev/null
+++ b/test/xray/TestCases/Linux/argv0-log-file-name.cc
@@ -0,0 +1,14 @@
+// Check to make sure argv[0] is contained within the (randomised) XRay log file
+// name.
+
+// RUN: %clangxx_xray -std=c++11 %s -o %t
+// RUN: %run %t > xray.log.file.name 2>&1
+// RUN: ls | FileCheck xray.log.file.name
+// RUN: rm xray-log.* xray.log.file.name
+
+#include <cstdio>
+#include <libgen.h>
+
+[[clang::xray_always_instrument]] int main(int argc, char *argv[]) {
+  printf("// CHECK: xray-log.%s.{{.*}}\n", basename(argv[0]));
+}