Fix `$stacktrace` to decode through internal-c++filt (#6985).

docs/guide/languages.rst

@@ -528,6 +528,12 @@ $readmemb, $readmemh
    specification do not include support for readmem to multi-dimensional
    arrays.
 
+$stacktrace
+   The `$stacktrace` system call will show the C++ stack, not the Verilog
+   call stack, though the function names typically correlate. To get
+   symbolic names, the model must have debug symbols, e.g. compile with
+   `-CFLAGS -ggdb -LDFLAGS -ggdb -LDFLAGS -rdynamic`.
+
 $test$plusargs, $value$plusargs
    Supported, but the instantiating C++/SystemC wrapper must call
 

docs/spelling.txt

@@ -1102,6 +1102,7 @@ src
 srcdir
 srcfile
 sscanf
+stacktrace
 stderr
 stdin
 stdout

include/verilated.cpp

@@ -69,6 +69,7 @@
 # include <direct.h>  // mkdir
 #endif
 #ifdef __GLIBC__
+# include <cxxabi.h>
 # include <execinfo.h>
 # define _VL_HAVE_STACKTRACE
 #endif
@@ -1918,6 +1919,40 @@ IData VL_FREAD_I(int width, int array_lsb, int array_size, void* memp, IData fpi
     return read_count;
 }
 
+#ifdef _VL_HAVE_STACKTRACE
+static std::string _vl_stacktrace_demangle(const std::string& input) {
+    std::string result;
+    result.reserve(input.size());
+
+    std::string word;
+    for (const char c : input) {
+        if (std::isalpha(c) || c == '_') {
+            word += c;
+        } else if (!word.empty() && std::isdigit(c)) {
+            word += c;
+        } else {
+            if (!word.empty()) {
+                // abi::__cxa_demangle mallocs demangled_name
+                int status = 0;
+                char* const demangled_name
+                    = abi::__cxa_demangle(word.c_str(), NULL, NULL, &status);
+                if (status == 0) {
+                    result += std::string{demangled_name};
+                    std::free(demangled_name);  // Free the allocated memory
+                } else {
+                    result += word;
+                }
+                word.clear();
+            }
+            result += c;
+        }
+    }
+    // input requires final newline, so last word can't be symbol
+    result += word;
+    return result;
+}
+#endif
+
 std::string VL_STACKTRACE_N() VL_MT_SAFE {
     static VerilatedMutex s_stackTraceMutex;
     const VerilatedLockGuard lock{s_stackTraceMutex};
@@ -1935,8 +1970,12 @@ std::string VL_STACKTRACE_N() VL_MT_SAFE {
     // cppcheck-suppress knownConditionTrueFalse
     if (!strings) return "Unable to backtrace\n";
 
+#ifdef _VL_HAVE_STACKTRACE
     std::string result = "Backtrace:\n";
-    for (int j = 0; j < nptrs; ++j) result += std::string{strings[j]} + "\n"s;
+    for (int j = 0; j < nptrs; ++j)
+        result += _vl_stacktrace_demangle(std::string{strings[j]} + "\n"s);
+#endif
+
     free(strings);
     return result;
 }

test_regress/t/t_stacktrace.py

@@ -11,7 +11,7 @@ import vltest_bootstrap
 
 test.scenarios('simulator')
 
-test.compile()
+test.compile(verilator_flags2=['-CFLAGS -ggdb -LDFLAGS -ggdb -LDFLAGS -rdynamic'])
 
 test.execute()
 

test_regress/t/t_stacktrace.v

@@ -6,22 +6,22 @@
 
 module t;
 
-   task automatic t;
-      // verilator no_inline_task
-      string trace;
+  task automatic t;
+    // verilator no_inline_task
+    string trace;
 
-      $display("== Trace Func");
-      trace = $stacktrace();
-      if (trace == "") $stop;
-      $display("%s", trace);
+    $display("== Trace Func");
+    trace = $stacktrace();
+    if (trace == "") $stop;
+    $display("%s", trace);
 
-      $display("== Trace Task");
-      $stacktrace;
+    $display("== Trace Task");
+    $stacktrace;
 
-      $write("*-* All Finished *-*\n");
-      $finish;
-   endtask
+    $write("*-* All Finished *-*\n");
+    $finish;
+  endtask
 
-   initial t();
+  initial t();
 
 endmodule