Reland "Support names field in source maps" (#25928)

This relands #25870. #25870 was reverted in #25923 due to CI errors
(https://app.circleci.com/pipelines/github/emscripten-core/emscripten/47832/workflows/ea0292aa-124d-4a3f-b988-0a96823e9bcd/jobs/1089017/tests),
which were fixed by
WebAssembly/binaryen#8113.

Author: aheejin

ChangeLog.md

@@ -20,6 +20,10 @@ See docs/process.md for more on how version tagging works.
 
 4.0.22 (in development)
 -----------------------
+- Source maps now support 'names' field with function name information.
+  emsymbolizer will show function names when used with a source map. The size
+  of source maps may increase 2-3x and the link time can increase slightly due
+  to more processing on source map creation. (#25298)
 - Emscripten will now cache the JS code that it generates and re-use when
   linking with the same settings at a later date.  This should improve link
   times generally but should especially noticeable when linking lots of small

test/core/test_dwarf.cpp

@@ -0,0 +1,26 @@
+#include <emscripten.h>
+
+EM_JS(int, out_to_js, (int x), {})
+
+class MyClass {
+public:
+  void foo();
+  void bar();
+};
+
+void __attribute__((noinline)) MyClass::foo() {
+  out_to_js(0); // line 12
+  out_to_js(1);
+  out_to_js(2);
+}
+
+void __attribute__((always_inline)) MyClass::bar() {
+  out_to_js(3);
+  __builtin_trap(); // line 19
+}
+
+int main() {
+  MyClass mc;
+  mc.foo();
+  mc.bar();
+}

test/test_other.py

@@ -9629,12 +9629,49 @@ def check_dwarf_loc_info(address, funcs, locs):
       for loc in locs:
         self.assertIn(loc, out)
 
-    def check_source_map_loc_info(address, loc):
+    def check_source_map_loc_info(address, func, loc):
       out = self.run_process(
           [emsymbolizer, '-s', 'sourcemap', 'test_dwarf.wasm', address],
           stdout=PIPE).stdout
+      self.assertIn(func, out)
       self.assertIn(loc, out)
 
+    def do_tests(src):
+      # 1. Test DWARF + source map together
+      # For DWARF, we check for the full inlined info for both function names and
+      # source locations. Source maps does not provide inlined info. So we only
+      # check for the info of the outermost function.
+      self.run_process([EMCC, test_file(src), '-g', '-gsource-map', '-O1', '-o',
+                        'test_dwarf.js'])
+      check_dwarf_loc_info(out_to_js_call_addr, out_to_js_call_func,
+                           out_to_js_call_loc)
+      check_source_map_loc_info(out_to_js_call_addr, out_to_js_call_func[0],
+                                out_to_js_call_loc[0])
+      check_dwarf_loc_info(unreachable_addr, unreachable_func, unreachable_loc)
+      # Source map shows the original (inlined) source location with the original
+      # function name
+      check_source_map_loc_info(unreachable_addr, unreachable_func[0],
+                                unreachable_loc[0])
+
+      # 2. Test source map only
+      # The addresses, function names, and source locations are the same across
+      # the builds because they are relative offsets from the code section, so we
+      # don't need to recompute them
+      self.run_process([EMCC, test_file(src), '-gsource-map', '-O1', '-o',
+                        'test_dwarf.js'])
+      check_source_map_loc_info(out_to_js_call_addr, out_to_js_call_func[0],
+                                out_to_js_call_loc[0])
+      check_source_map_loc_info(unreachable_addr, unreachable_func[0],
+                                unreachable_loc[0])
+
+      # 3. Test DWARF only
+      self.run_process([EMCC, test_file(src), '-g', '-O1', '-o',
+                        'test_dwarf.js'])
+      check_dwarf_loc_info(out_to_js_call_addr, out_to_js_call_func,
+                           out_to_js_call_loc)
+      check_dwarf_loc_info(unreachable_addr, unreachable_func, unreachable_loc)
+
+    # -- C program test --
     # We test two locations within test_dwarf.c:
     # out_to_js(0);     // line 6
     # __builtin_trap(); // line 13
@@ -9657,31 +9694,32 @@ def check_source_map_loc_info(address, loc):
     # The first one corresponds to the innermost inlined location.
     unreachable_loc = ['test_dwarf.c:13:3', 'test_dwarf.c:18:3']
 
-    # 1. Test DWARF + source map together
-    # For DWARF, we check for the full inlined info for both function names and
-    # source locations. Source maps provide neither function names nor inlined
-    # info. So we only check for the source location of the outermost function.
-    check_dwarf_loc_info(out_to_js_call_addr, out_to_js_call_func,
-                         out_to_js_call_loc)
-    check_source_map_loc_info(out_to_js_call_addr, out_to_js_call_loc[0])
-    check_dwarf_loc_info(unreachable_addr, unreachable_func, unreachable_loc)
-    check_source_map_loc_info(unreachable_addr, unreachable_loc[0])
-
-    # 2. Test source map only
-    # The addresses, function names, and source locations are the same across
-    # the builds because they are relative offsets from the code section, so we
-    # don't need to recompute them
-    self.run_process([EMCC, test_file('core/test_dwarf.c'),
-                      '-gsource-map', '-O1', '-o', 'test_dwarf.js'])
-    check_source_map_loc_info(out_to_js_call_addr, out_to_js_call_loc[0])
-    check_source_map_loc_info(unreachable_addr, unreachable_loc[0])
+    do_tests('core/test_dwarf.c')
 
-    # 3. Test DWARF only
-    self.run_process([EMCC, test_file('core/test_dwarf.c'),
-                      '-g', '-O1', '-o', 'test_dwarf.js'])
-    check_dwarf_loc_info(out_to_js_call_addr, out_to_js_call_func,
-                         out_to_js_call_loc)
-    check_dwarf_loc_info(unreachable_addr, unreachable_func, unreachable_loc)
+    # -- C++ program test --
+    # We test two locations within test_dwarf.cpp:
+    # out_to_js(0);     // line 12
+    # __builtin_trap(); // line 19
+    self.run_process([EMCC, test_file('core/test_dwarf.cpp'),
+                      '-g', '-gsource-map', '-O1', '-o', 'test_dwarf.js'])
+    # Address of out_to_js(0) within MyClass::foo(), uninlined
+    out_to_js_call_addr = self.get_instr_addr('call\t0', 'test_dwarf.wasm')
+    # Address of __builtin_trap() within MyClass::bar(), inlined into main()
+    unreachable_addr = self.get_instr_addr('unreachable', 'test_dwarf.wasm')
+
+    # Function name of out_to_js(0) within MyClass::foo(), uninlined
+    out_to_js_call_func = ['MyClass::foo()']
+    # Function names of __builtin_trap() within MyClass::bar(), inlined into
+    # main(). The first one corresponds to the innermost inlined function.
+    unreachable_func = ['MyClass::bar()', 'main']
+
+    # Source location of out_to_js(0) within MyClass::foo(), uninlined
+    out_to_js_call_loc = ['test_dwarf.cpp:12:3']
+    # Source locations of __builtin_trap() within MyClass::bar(), inlined into
+    # main(). The first one corresponds to the innermost inlined location.
+    unreachable_loc = ['test_dwarf.cpp:19:3', 'test_dwarf.cpp:25:6']
+
+    do_tests('core/test_dwarf.cpp')
 
   def test_emsymbolizer_functions(self):
     'Test emsymbolizer use cases that only provide function-granularity info'

tools/emsymbolizer.py

@@ -117,6 +117,7 @@ class Location:
   def __init__(self):
     self.version = None
     self.sources = []
+    self.funcs = []
     self.mappings = {}
     self.offsets = []
 
@@ -128,6 +129,7 @@ def parse(self, filename):
 
     self.version = source_map_json['version']
     self.sources = source_map_json['sources']
+    self.funcs = source_map_json['names']
 
     chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/='
     vlq_map = {c: i for i, c in enumerate(chars)}
@@ -155,6 +157,7 @@ def decodeVLQ(string):
     src = 0
     line = 1
     col = 1
+    func = 0
     for segment in source_map_json['mappings'].split(','):
       data = decodeVLQ(segment)
       info = []
@@ -169,7 +172,9 @@ def decodeVLQ(string):
       if len(data) >= 4:
         col += data[3]
         info.append(col)
-      # TODO: see if we need the name, which is the next field (data[4])
+      if len(data) == 5:
+        func += data[4]
+        info.append(func)
 
       self.mappings[offset] = WasmSourceMap.Location(*info)
       self.offsets.append(offset)
@@ -207,6 +212,7 @@ def lookup(self, offset, lower_bound=None):
         self.sources[info.source] if info.source is not None else None,
         info.line,
         info.column,
+        self.funcs[info.func] if info.func is not None else None,
       )