Uses SNPRINT macro where possible. Otherwise uses #define for format.

runtime/vm/os_android.cc

Index: runtime/vm/os_android.cc
diff --git a/runtime/vm/os_android.cc b/runtime/vm/os_android.cc
index 676e2780a7058f5fa7b1559a1c7b11ba1dc02ec4..e100011058087e481325b5728c2b48be45549c88 100644
--- a/runtime/vm/os_android.cc
+++ b/runtime/vm/os_android.cc
@@ -44,12 +44,10 @@ class PerfCodeObserver : public CodeObserver {
     if (file_open == NULL) {
       return;
     }
-    const char* format = "/tmp/perf-%ld.map";
     intptr_t pid = getpid();
-    intptr_t len = OS::SNPrint(NULL, 0, format, pid);
-    char* filename = new char[len + 1];
-    OS::SNPrint(filename, len + 1, format, pid);
+    char* filename = OS::SNCreate(NULL, "/tmp/perf-%" Pd ".map", pid);
     out_file_ = (*file_open)(filename, true);
+    free(filename);
   }
 
   ~PerfCodeObserver() {
@@ -73,12 +71,10 @@ class PerfCodeObserver : public CodeObserver {
     if ((file_write == NULL) || (out_file_ == NULL)) {
       return;
     }
-    const char* format = "%" Px " %" Px " %s%s\n";
     const char* marker = optimized ? "*" : "";
-    intptr_t len = OS::SNPrint(NULL, 0, format, base, size, marker, name);
-    char* buffer = Thread::Current()->zone()->Alloc<char>(len + 1);
-    OS::SNPrint(buffer, len + 1, format, base, size, marker, name);
-    (*file_write)(buffer, len, out_file_);
+    char* buffer = OS::SNCreate(Thread::Current()->zone(),
+        "%" Px " %" Px " %s%s\n", base, size, marker, name);
+    (*file_write)(buffer, strlen(buffer), out_file_);
   }
 
  private:
@@ -107,10 +103,8 @@ class GdbCodeObserver : public CodeObserver {
       // the prologue sequence is not the first instruction:
       // <name>_entry is used for code preceding the prologue sequence.
       // <name> for rest of the code (first instruction is prologue sequence).
-      const char* kFormat = "%s_%s";
-      intptr_t len = OS::SNPrint(NULL, 0, kFormat, name, "entry");
-      char* pname = Thread::Current()->zone()->Alloc<char>(len + 1);
-      OS::SNPrint(pname, (len + 1), kFormat, name, "entry");
+      char* pname = OS::SNCreate(Thread::Current()->zone(),
+          "%s_%s", name, "entry");
       DebugInfo::RegisterSection(pname, base, size);
       DebugInfo::RegisterSection(name,
                                  (base + prologue_offset),
@@ -345,6 +339,34 @@ int OS::SNPrint(char* str, size_t size, const char* format, ...) {
 }
 
 
+char* OS::SNCreate(Zone* zone, const char* format, ...) {

[Ivan Posva, 2015/09/10 18:08:11]

P.S. Please drop the N as we are not passing a length here. I missed that in the
original review, sorry.

[zra, 2015/09/10 21:58:38]

Done.

+  va_list args;
+  va_start(args, format);
+
+  // Measure.
+  va_list measure_args;
+  va_copy(measure_args, args);
+  intptr_t len = VSNPrint(NULL, 0, format, measure_args);
+  va_end(measure_args);
+
+  char* buffer;
+  if (zone) {
+    buffer = zone->Alloc<char>(len + 1);

[Cutch, 2015/09/10 18:01:04]

Note that Zone already has the following utility functions:

char* PrintToString(const char* format, ...) PRINTF_ATTRIBUTE(2, 3);
char* VPrint(const char* format, va_list args);

[Ivan Posva, 2015/09/10 18:08:11]

Thanks for pointing that out. I find that API a bit confusing since it does not
print the Zone, but allocates from the Zone. We should probably consolidate
these uses with this API here.

[zra, 2015/09/10 21:58:38]

Changed as discussed this morning.

+  } else {
+    buffer = reinterpret_cast<char*>(malloc(len + 1));
+  }
+  ASSERT(buffer != NULL);
+
+  // Print.
+  va_list print_args;
+  va_copy(print_args, args);
+  VSNPrint(buffer, len + 1, format, print_args);
+  va_end(print_args);
+  va_end(args);
+  return buffer;
+}
+
+
 int OS::VSNPrint(char* str, size_t size, const char* format, va_list args) {
   int retval = vsnprintf(str, size, format, args);
   if (retval < 0) {