Implements profiling support by hooking into the function execution. qjs outputs chrome devtools-compatible profiling data

Makefile

@@ -53,6 +53,9 @@ PREFIX?=/usr/local
 
 # include the code for BigFloat/BigDecimal and math mode
 CONFIG_BIGNUM=y
+# Include code for profiling individual function calls.
+# qjs will produce a file compatible with chrome devtools and other tools.
+# CONFIG_PROFILE_CALLS=y
 
 OBJDIR=.obj
 
@@ -148,6 +151,9 @@ ifeq ($(shell $(CC) -o /dev/null compat/test-closefrom.c 2>/dev/null && echo 1),
 DEFINES+=-DHAVE_CLOSEFROM
 endif
 endif
+ifdef CONFIG_PROFILE_CALLS
+DEFINES+=-DCONFIG_PROFILE_CALLS
+endif
 
 CFLAGS+=$(DEFINES)
 CFLAGS_DEBUG=$(CFLAGS) -O0

qjs.c

@@ -289,6 +289,10 @@ void help(void)
 #endif
            "-T  --trace        trace memory allocation\n"
            "-d  --dump         dump the memory usage stats\n"
+#ifdef CONFIG_PROFILE_CALLS
+           "-p  --profile FILE dump the profiling stats to FILENAME in a format that can be open in chromium devtools\n"
+           "    --profile-sampling n collect function calls every 1/n times. Defaults to 1 (i.e. every call)\n"
+#endif
            "    --memory-limit n       limit the memory usage to 'n' bytes\n"
            "    --stack-size n         limit the stack size to 'n' bytes\n"
            "    --unhandled-rejection  dump unhandled promise rejections\n"
@@ -296,6 +300,39 @@ void help(void)
     exit(1);
 }
 
+#ifdef CONFIG_PROFILE_CALLS
+void profile_function_start(JSContext *ctx, JSAtom func, JSAtom filename, void *opaque) {
+    const char* func_str = JS_AtomToCString(ctx, func);
+    const char *func_str2 = func_str[0] ? func_str : "<anonymous>";
+    FILE *logfile = (FILE *)opaque;
+    // Format documented here:
+    // https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/preview?tab=t.0#heading=h.yr4qxyxotyw
+    fprintf(logfile, "{"
+            "\"name\": \"%s\","
+            "\"cat\": \"js\","
+            "\"ph\": \"B\","
+            "\"ts\": %ld,"
+            "\"pid\": 1,"
+            "\"tid\": 1"
+        "},\n", func_str2, clock());
+    JS_FreeCString(ctx, func_str);
+}
+void profile_function_end(JSContext *ctx, JSAtom func, JSAtom filename, void *opaque) {
+    const char* func_str = JS_AtomToCString(ctx, func);
+    const char *func_str2 = func_str[0] ? func_str : "<anonymous>";
+    FILE *logfile = (FILE *)opaque;
+    fprintf(logfile, "{"
+            "\"name\": \"%s\","
+            "\"cat\": \"js\","
+            "\"ph\": \"E\","
+            "\"ts\": %ld,"
+            "\"pid\": 1,"
+            "\"tid\": 1"
+        "},\n", func_str2, clock());
+    JS_FreeCString(ctx, func_str);
+}
+#endif
+
 int main(int argc, char **argv)
 {
     JSRuntime *rt;
@@ -306,6 +343,10 @@ int main(int argc, char **argv)
     int interactive = 0;
     int dump_memory = 0;
     int trace_memory = 0;
+#ifdef CONFIG_PROFILE_CALLS
+    FILE *profile_file = NULL;
+    uint32_t profile_sampling = 1;
+#endif
     int empty_run = 0;
     int module = -1;
     int load_std = 0;
@@ -399,6 +440,29 @@ int main(int argc, char **argv)
                 trace_memory++;
                 continue;
             }
+#ifdef CONFIG_PROFILE_CALLS
+            if (opt == 'p' || !strcmp(longopt, "profile")) {
+                if (*arg) {
+                    profile_file = fopen(arg, "w");
+                    break;
+                }
+                if (optind < argc) {
+                    profile_file = fopen(argv[optind++], "w");
+                    break;
+                }
+                fprintf(stderr, "qjs: missing filename for -p\n");
+                exit(1);
+                continue;
+            }
+            if (!strcmp(longopt, "profile-sampling")) {
+                if (optind >= argc) {
+                    fprintf(stderr, "expecting profile sampling");
+                    exit(1);
+                }
+                profile_sampling = (uint32_t)strtod(argv[optind++], NULL);
+                continue;
+            }
+#endif
             if (!strcmp(longopt, "std")) {
                 load_std = 1;
                 continue;
@@ -461,6 +525,12 @@ int main(int argc, char **argv)
         fprintf(stderr, "qjs: cannot allocate JS runtime\n");
         exit(2);
     }
+#ifdef CONFIG_PROFILE_CALLS
+    if(profile_file) {
+        JS_EnableProfileCalls(rt, profile_function_start, profile_function_end, profile_sampling, profile_file);
+        fprintf(profile_file, "{\"traceEvents\": [");
+    }
+#endif
     if (memory_limit != 0)
         JS_SetMemoryLimit(rt, memory_limit);
     if (stack_size != 0)
@@ -530,6 +600,13 @@ int main(int argc, char **argv)
     js_std_free_handlers(rt);
     JS_FreeContext(ctx);
     JS_FreeRuntime(rt);
+#ifdef CONFIG_PROFILE_CALLS
+    if(profile_file) {
+        // Inject an instant event at the end just to make sure it's valid JSON.
+        fprintf(profile_file, R"({"name": "end", "ph": "I", "ts": %ld, "pid": 1, "tid": 1, "s": "g"}]})", clock());
+        fclose(profile_file);
+    }
+#endif
 
     if (empty_run && dump_memory) {
         clock_t t[5];

quickjs.c

@@ -302,6 +302,13 @@ struct JSRuntime {
     JSNumericOperations bigfloat_ops;
     JSNumericOperations bigdecimal_ops;
     uint32_t operator_count;
+#endif
+#ifdef CONFIG_PROFILE_CALLS
+    ProfileEventHandler *profile_function_start;
+    ProfileEventHandler *profile_function_end;
+    void *profile_opaque;
+    uint32_t profile_sampling;
+    uint32_t profile_sample_count;
 #endif
     void *user_opaque;
 };
@@ -621,6 +628,10 @@ typedef struct JSFunctionBytecode {
         int pc2line_len;
         uint8_t *pc2line_buf;
         char *source;
+#ifdef CONFIG_PROFILE_CALLS
+        /* Class.function or Object.function or just function */
+        JSAtom full_func_name_cache;
+#endif
     } debug;
 } JSFunctionBytecode;
 
@@ -5546,8 +5557,17 @@ void __JS_FreeValueRT(JSRuntime *rt, JSValue v)
             }
         }
         break;
-    case JS_TAG_OBJECT:
     case JS_TAG_FUNCTION_BYTECODE:
+#ifdef CONFIG_PROFILE_CALLS
+    {
+        JSFunctionBytecode *b = JS_VALUE_GET_PTR(v);
+        // In STRICT js_mode, there is no "debug".
+        if (!(b->js_mode & JS_MODE_STRICT) && b->debug.full_func_name_cache != JS_ATOM_NULL) {
+            JS_FreeAtomRT(rt, b->debug.full_func_name_cache);
+        }
+    }
+#endif
+    case JS_TAG_OBJECT:
         {
             JSGCObjectHeader *p = JS_VALUE_GET_PTR(v);
             if (rt->gc_phase != JS_GC_PHASE_REMOVE_CYCLES) {
@@ -5881,6 +5901,20 @@ BOOL JS_IsLiveObject(JSRuntime *rt, JSValueConst obj)
     return !p->free_mark;
 }
 
+void JS_EnableProfileCalls(JSRuntime *rt, ProfileEventHandler *on_start, ProfileEventHandler *on_end, uint32_t sampling, void *opaque_data)
+{
+#ifdef CONFIG_PROFILE_CALLS
+    rt->profile_function_start = on_start;
+    rt->profile_function_end = on_end;
+    rt->profile_opaque = opaque_data;
+    // If sampling == 0, it's interpreted as "no sampling" which means we log 1/1 calls.
+    rt->profile_sampling = sampling > 0 ? sampling : 1;
+    rt->profile_sample_count = 0;
+#else
+    fprintf(stderr, "QuickJS was not compiled with -DCONFIG_PROFILE_CALLS. Profiling is disabled.");
+#endif
+}
+
 /* Compute memory used by various object types */
 /* XXX: poor man's approach to handling multiply referenced objects */
 typedef struct JSMemoryUsage_helper {
@@ -6529,6 +6563,64 @@ static const char *get_func_name(JSContext *ctx, JSValueConst func)
     return JS_ToCString(ctx, val);
 }
 
+/* Computes the full name of the function including the constructor of the
+   object it's being executed on, if any. For example, this may output
+   "MyClass.my_function" or if there is no "this", just "my_function". */
+static JSAtom get_full_func_name(JSContext *ctx, JSValueConst func, JSValueConst this_obj)
+{
+    JSAtom result_atom;
+    const char *func_str = get_func_name(ctx, func);
+    if (!func_str || func_str[0] == '\0') {
+        JS_FreeCString(ctx, func_str);
+        return JS_ATOM_NULL;
+    }
+    // If "this" isn't an object, return just the name.
+    if (JS_VALUE_GET_TAG(this_obj) != JS_TAG_OBJECT) {
+        result_atom = JS_NewAtom(ctx, func_str);
+        JS_FreeCString(ctx, func_str);
+        return result_atom;
+    }
+
+    JSValue ctor = JS_GetProperty(ctx, this_obj, JS_ATOM_constructor);
+    const char *ctor_str = get_func_name(ctx, ctor);
+    size_t func_len = strlen(func_str);
+    JSValue result_val;
+
+    if (ctor_str == NULL || ctor_str[0] == '\0') {
+        // Invalid constructor, use <unknown>
+        StringBuffer sb;
+        char prefix[] = "<unknown>.";
+        if (string_buffer_init2(ctx, &sb, sizeof(prefix) + func_len, 0)) {
+            JS_FreeCString(ctx, func_str);
+            JS_FreeCString(ctx, ctor_str);
+            JS_FreeValue(ctx, ctor);
+            return JS_ATOM_NULL;
+        }
+        string_buffer_write8(&sb, (const uint8_t *)prefix, sizeof(prefix));
+        string_buffer_write8(&sb, (const uint8_t *)func_str, func_len);
+        result_val = string_buffer_end(&sb);
+    } else {
+        StringBuffer sb;
+        size_t ctor_len = strlen(ctor_str);
+        if (string_buffer_init2(ctx, &sb, ctor_len + 1 + func_len, 0)) {
+            JS_FreeCString(ctx, func_str);
+            JS_FreeCString(ctx, ctor_str);
+            JS_FreeValue(ctx, ctor);
+            return JS_ATOM_NULL;
+        }
+        string_buffer_write8(&sb, (const uint8_t *)ctor_str, ctor_len);
+        string_buffer_write8(&sb, (const uint8_t *)".", 1);
+        string_buffer_write8(&sb, (const uint8_t *)func_str, func_len);
+        result_val = string_buffer_end(&sb);
+    }
+    result_atom = JS_ValueToAtom(ctx, result_val);
+    JS_FreeValue(ctx, result_val);
+    JS_FreeCString(ctx, func_str);
+    JS_FreeCString(ctx, ctor_str);
+    JS_FreeValue(ctx, ctor);
+    return result_atom;
+}
+
 #define JS_BACKTRACE_FLAG_SKIP_FIRST_LEVEL (1 << 0)
 /* only taken into account if filename is provided */
 #define JS_BACKTRACE_FLAG_SINGLE_LEVEL     (1 << 1)
@@ -16169,6 +16261,10 @@ static JSValue JS_CallInternal(JSContext *caller_ctx, JSValueConst func_obj,
     JSValue *local_buf, *stack_buf, *var_buf, *arg_buf, *sp, ret_val, *pval;
     JSVarRef **var_refs;
     size_t alloca_size;
+#ifdef CONFIG_PROFILE_CALLS
+    JSAtom full_func_name = JS_ATOM_NULL;
+    const int must_sample = rt->profile_sampling && rt->profile_sample_count == 0;
+#endif
 
 #if !DIRECT_DISPATCH
 #define SWITCH(pc)      switch (opcode = *pc++)
@@ -16232,7 +16328,22 @@ static JSValue JS_CallInternal(JSContext *caller_ctx, JSValueConst func_obj,
                          (JSValueConst *)argv, flags);
     }
     b = p->u.func.function_bytecode;
-
+#ifdef CONFIG_PROFILE_CALLS
+    if (unlikely(must_sample)) {
+        if (!(b->js_mode & JS_MODE_STRICT)) {
+            if (!b->debug.full_func_name_cache) {
+                b->debug.full_func_name_cache = get_full_func_name(caller_ctx, func_obj, this_obj);
+            }
+            full_func_name = b->debug.full_func_name_cache;
+        } else {
+            // Even if we can't cache it, we need to compute it to report the function execution.
+            full_func_name = get_full_func_name(caller_ctx, func_obj, this_obj);
+        }
+        if (likely(rt->profile_function_start)) {
+            rt->profile_function_start(caller_ctx, full_func_name, b->debug.filename, rt->profile_opaque);
+        }
+    }
+#endif
     if (unlikely(argc < b->arg_count || (flags & JS_CALL_FLAG_COPY_ARGV))) {
         arg_allocated_size = b->arg_count;
     } else {
@@ -18701,6 +18812,20 @@ static JSValue JS_CallInternal(JSContext *caller_ctx, JSValueConst func_obj,
         }
     }
     rt->current_stack_frame = sf->prev_frame;
+#ifdef CONFIG_PROFILE_CALLS
+    if (unlikely(must_sample)) {
+        if (likely(rt->profile_function_end)) {
+            rt->profile_function_end(caller_ctx, full_func_name, b->debug.filename, rt->profile_opaque);
+        }
+        if (b->js_mode & JS_MODE_STRICT) {
+            // If we weren't able to cache it, we have to free it right away (and sadly recreate it later).
+            JS_FreeAtom(caller_ctx, full_func_name);
+        }
+    }
+    if (unlikely(rt->profile_sampling)) {
+        rt->profile_sample_count = (rt->profile_sample_count + 1) % rt->profile_sampling;
+    }
+#endif
     return ret_val;
 }
 

quickjs.h

@@ -350,6 +350,31 @@ void JS_MarkValue(JSRuntime *rt, JSValueConst val, JS_MarkFunc *mark_func);
 void JS_RunGC(JSRuntime *rt);
 JS_BOOL JS_IsLiveObject(JSRuntime *rt, JSValueConst obj);
 
+/**
+ * Callback function type for handling JavaScript profiling events.
+ *
+ * @param func        Function name as a JSAtom. May be in the format "Constructor.name"
+ *                    when the function is executed in a constructor's context (i.e.,
+ *                    with 'this' binding)
+ * @param filename    Name of the source file containing the function, as a JSAtom
+ * @param opaque_data User data that was originally passed to JS_EnableProfileCalls.
+ *                    Same value is provided to both start and end handlers
+ */
+typedef void ProfileEventHandler(JSContext *ctx, JSAtom func, JSAtom filename, void *opaque_data);
+/**
+ * Enables function call profiling for the JavaScript runtime.
+ *
+ * NOTE: This function only works if QuickJS was compiled with -DCONFIG_PROFILE_CALLS flag.
+ *
+ * @param on_start    Callback called when a function starts.
+ * @param on_end      Callback called when a function ends.
+ * @param sampling    Controls profiling frequency: only 1/sampling function calls are
+ *                    instrumented. Must be ≥ 1. Example: if sampling=4, only 25% of
+ *                    function calls will trigger the handlers.
+ * @param opaque_data Optional user data passed to both handlers. Can be NULL.
+ */
+void JS_EnableProfileCalls(JSRuntime *rt, ProfileEventHandler *on_start, ProfileEventHandler *on_end, uint32_t sampling, void *opaque_data);
+
 JSContext *JS_NewContext(JSRuntime *rt);
 void JS_FreeContext(JSContext *s);
 JSContext *JS_DupContext(JSContext *ctx);