Support new dylink.0 custom section format (emscripten-core#15019)

See also:
llvm change: https://reviews.llvm.org/D109595
wabt change: WebAssembly/wabt#1707
binaryen change: WebAssembly/binaryen#4141

Author: sbc100

src/library_dylink.js

@@ -256,60 +256,104 @@ var LibraryDylink = {
   // returns the side module metadata as an object
   // { memorySize, memoryAlign, tableSize, tableAlign, neededDynlibs}
   $getDylinkMetadata: function(binary) {
-    var next = 0;
+    var offset = 0;
+    var end = 0;
+
+    function getU8() {
+      return binary[offset++];
+    }
+
     function getLEB() {
       var ret = 0;
       var mul = 1;
       while (1) {
-        var byte = binary[next++];
+        var byte = binary[offset++];
         ret += ((byte & 0x7f) * mul);
         mul *= 0x80;
         if (!(byte & 0x80)) break;
       }
       return ret;
     }
 
+    function getString() {
+      var len = getLEB();
+      offset += len;
+      return UTF8ArrayToString(binary, offset - len, len);
+    }
+
+    var name = 'dylink.0';
     if (binary instanceof WebAssembly.Module) {
-      var dylinkSection = WebAssembly.Module.customSections(binary, "dylink");
+      var dylinkSection = WebAssembly.Module.customSections(binary, name);
+      if (dylinkSection.length === 0) {
+        name = 'dylink'
+        dylinkSection = WebAssembly.Module.customSections(binary, name);
+      }
       assert(dylinkSection.length != 0, 'need dylink section');
       binary = new Uint8Array(dylinkSection[0]);
+      end = binary.length
     } else {
       var int32View = new Uint32Array(new Uint8Array(binary.subarray(0, 24)).buffer);
       assert(int32View[0] == 0x6d736100, 'need to see wasm magic number'); // \0asm
-      // we should see the dylink section right after the magic number and wasm version
+      // we should see the dylink custom section right after the magic number and wasm version
       assert(binary[8] === 0, 'need the dylink section to be first')
-      next = 9;
-      getLEB(); //section size
-      assert(binary[next] === 6);                 next++; // size of "dylink" string
-      assert(binary[next] === 'd'.charCodeAt(0)); next++;
-      assert(binary[next] === 'y'.charCodeAt(0)); next++;
-      assert(binary[next] === 'l'.charCodeAt(0)); next++;
-      assert(binary[next] === 'i'.charCodeAt(0)); next++;
-      assert(binary[next] === 'n'.charCodeAt(0)); next++;
-      assert(binary[next] === 'k'.charCodeAt(0)); next++;
-    }
-
-    var customSection = {};
-    customSection.memorySize = getLEB();
-    customSection.memoryAlign = getLEB();
-    customSection.tableSize = getLEB();
-    customSection.tableAlign = getLEB();
+      offset = 9;
+      var section_size = getLEB(); //section size
+      end = offset + section_size;
+      name = getString();
+    }
+
+    var customSection = { neededDynlibs: [] };
+    if (name == 'dylink') {
+      customSection.memorySize = getLEB();
+      customSection.memoryAlign = getLEB();
+      customSection.tableSize = getLEB();
+      customSection.tableAlign = getLEB();
+      // shared libraries this module needs. We need to load them first, so that
+      // current module could resolve its imports. (see tools/shared.py
+      // WebAssembly.make_shared_library() for "dylink" section extension format)
+      var neededDynlibsCount = getLEB();
+      for (var i = 0; i < neededDynlibsCount; ++i) {
+        var name = getString();
+        customSection.neededDynlibs.push(name);
+      }
+    } else {
+      assert(name === 'dylink.0');
+      var WASM_DYLINK_MEM_INFO = 0x1;
+      var WASM_DYLINK_NEEDED = 0x2;
+      while (offset < end) {
+        var subsectionType = getU8();
+        var subsectionSize = getLEB();
+        if (subsectionType === WASM_DYLINK_MEM_INFO) {
+          customSection.memorySize = getLEB();
+          customSection.memoryAlign = getLEB();
+          customSection.tableSize = getLEB();
+          customSection.tableAlign = getLEB();
+        } else if (subsectionType === WASM_DYLINK_NEEDED) {
+          var neededDynlibsCount = getLEB();
+          for (var i = 0; i < neededDynlibsCount; ++i) {
+            var name = getString();
+            customSection.neededDynlibs.push(name);
+          }
+        } else {
+#if ASSERTIONS
+          err('unknown dylink.0 subsection: ' + subsectionType)
+#endif
+          // unknown subsection
+          offset += subsectionSize;
+        }
+      }
+    }
+
 #if ASSERTIONS
     var tableAlign = Math.pow(2, customSection.tableAlign);
     assert(tableAlign === 1, 'invalid tableAlign ' + tableAlign);
 #endif
-    // shared libraries this module needs. We need to load them first, so that
-    // current module could resolve its imports. (see tools/shared.py
-    // WebAssembly.make_shared_library() for "dylink" section extension format)
-    var neededDynlibsCount = getLEB();
-    customSection.neededDynlibs = [];
-    for (var i = 0; i < neededDynlibsCount; ++i) {
-      var nameLen = getLEB();
-      var nameUTF8 = binary.subarray(next, next + nameLen);
-      next += nameLen;
-      var name = UTF8ArrayToString(nameUTF8, 0);
-      customSection.neededDynlibs.push(name);
-    }
+
+#if DYLINK_DEBUG
+    err('dylink needed:' + customSection.neededDynlibs);
+#endif
+
+    assert(offset == end);
     return customSection;
   },
 

tools/building.py

@@ -1266,7 +1266,7 @@ def is_wasm_dylib(filename):
   section = next(module.sections())
   if section.type == webassembly.SecType.CUSTOM:
     module.seek(section.offset)
-    if module.readString() == 'dylink':
+    if module.readString() in ('dylink', 'dylink.0'):
       return True
   return False
 

tools/webassembly.py

@@ -135,6 +135,11 @@ class ExternType(IntEnum):
   EVENT = 4
 
 
+class DylinkType(IntEnum):
+  MEM_INFO = 1
+  NEEDED = 2
+
+
 Section = namedtuple('Section', ['type', 'size', 'offset'])
 Limits = namedtuple('Limits', ['flags', 'initial', 'maximum'])
 Import = namedtuple('Import', ['kind', 'module', 'field'])
@@ -178,7 +183,13 @@ def readLimits(self):
     return Limits(flags, initial, maximum)
 
   def seek(self, offset):
-    self.buf.seek(offset)
+    return self.buf.seek(offset)
+
+  def tell(self):
+    return self.buf.tell()
+
+  def skip(self, count):
+    self.buf.seek(count, os.SEEK_CUR)
 
   def sections(self):
     """Generator that lazily returns sections from the wasm file."""
@@ -200,18 +211,43 @@ def parse_dylink_section(wasm_file):
   module.seek(dylink_section.offset)
   # section name
   section_name = module.readString()
-  assert section_name == 'dylink'
-  mem_size = module.readULEB()
-  mem_align = module.readULEB()
-  table_size = module.readULEB()
-  table_align = module.readULEB()
-
   needed = []
-  needed_count = module.readULEB()
-  while needed_count:
-    libname = module.readString()
-    needed.append(libname)
-    needed_count -= 1
+
+  if section_name == 'dylink':
+    mem_size = module.readULEB()
+    mem_align = module.readULEB()
+    table_size = module.readULEB()
+    table_align = module.readULEB()
+
+    needed_count = module.readULEB()
+    while needed_count:
+      libname = module.readString()
+      needed.append(libname)
+      needed_count -= 1
+  elif section_name == 'dylink.0':
+    section_end = dylink_section.offset + dylink_section.size
+    while module.tell() < section_end:
+      subsection_type = module.readULEB()
+      subsection_size = module.readULEB()
+      end = module.tell() + subsection_size
+      if subsection_type == DylinkType.MEM_INFO:
+        mem_size = module.readULEB()
+        mem_align = module.readULEB()
+        table_size = module.readULEB()
+        table_align = module.readULEB()
+      elif subsection_type == DylinkType.NEEDED:
+        needed_count = module.readULEB()
+        while needed_count:
+          libname = module.readString()
+          needed.append(libname)
+          needed_count -= 1
+      else:
+        print(f'unknown subsection: {subsection_type}')
+        # ignore unknown subsections
+        module.skip(subsection_size)
+      assert(module.tell() == end)
+  else:
+    utils.exit_with_error('error parsing shared library')
 
   return Dylink(mem_size, mem_align, table_size, table_align, needed)