Fix null terminator in Demangle function.

If the demangled name is longer than out_size, the null terminator is
missing from the output. This will cause a crash in the DemangleInplace()
function (symbolize.cc) when calling strlen on the buffer.

src/demangle.cc

@@ -1350,7 +1350,13 @@ bool Demangle(const char* mangled, char* out, size_t out_size) {
     return false;
   }
 
-  std::copy_n(unmangled.get(), std::min(n, out_size), out);
+  if (out_size > 0) {
+    // n is the size of the allocated buffer, not the length of the string.
+    // Therefore, it includes the terminating zero (and possibly additional space).
+    std::size_t copy_size = std::min(n-1, out_size - 1);
+    std::copy_n(unmangled.get(), copy_size, out);
+    out[copy_size] = '\0'; // Ensure terminating null if n > out_size
+  }
   return status == 0;
 #else
   State state;

src/symbolize_unittest.cc

@@ -34,7 +34,11 @@
 #include "symbolize.h"
 
 #include <csignal>
+#include <cstring>
 #include <iostream>
+#include <map>
+#include <string>
+
 
 #include "config.h"
 #include "glog/logging.h"
@@ -133,6 +137,18 @@ TEST(Symbolize, Symbolize) {
 
 struct Foo {
   static void func(int x);
+  static size_t longParamFunc(
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p0,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p1,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p2,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p3,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p4,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p5,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p6,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p7,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p8,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p9
+		);
 };
 
 void ATTRIBUTE_NOINLINE Foo::func(int x) {
@@ -142,6 +158,21 @@ void ATTRIBUTE_NOINLINE Foo::func(int x) {
   a = a + 1;
 }
 
+size_t ATTRIBUTE_NOINLINE Foo::longParamFunc(
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p0,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p1,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p2,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p3,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p4,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p5,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p6,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p7,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p8,
+		std::map<std::map<std::string, std::string>,std::map<std::string, std::string> > p9
+		) {
+  return p0.size() + p1.size() + p2.size() + p3.size() + p4.size() + p5.size() + p6.size() + p7.size() + p8.size() + p9.size();
+}
+
 // With a modern GCC, Symbolize() should return demangled symbol
 // names.  Function parameters should be omitted.
 #    ifdef TEST_WITH_MODERN_GCC
@@ -150,6 +181,10 @@ TEST(Symbolize, SymbolizeWithDemangling) {
 #      if !defined(_MSC_VER) || !defined(NDEBUG)
 #        if defined(HAVE___CXA_DEMANGLE)
   EXPECT_STREQ("Foo::func(int)", TrySymbolize((void*)(&Foo::func)));
+  // Very long functions can be truncated, but we should not crash or return null.
+  // Also the result should start properly.
+  const char* symbol = TrySymbolize((void*)(&Foo::longParamFunc));
+  EXPECT_TRUE(symbol == std::strstr(symbol, "Foo::longParamFunc("));
 #        else
   EXPECT_STREQ("Foo::func()", TrySymbolize((void*)(&Foo::func)));
 #        endif