[WebAssembly] Add support for init functions linking metadata

Summary:
This change lays the groundwork lowering of @llvm.global_ctors
and @llvm.global_dtors for the wasm object format.  Some parts
of this patch are subset of: https://reviews.llvm.org/D40759

See https://github.com/WebAssembly/tool-conventions/issues/25

Subscribers: jfb, dschuff, jgravelle-google, aheejin, sunfish

Differential Revision: https://reviews.llvm.org/D41208

llvm-svn: 320742

2 files changed, 17 insertions, 2 deletions

diff --git a/llvm/tools/obj2yaml/wasm2yaml.cpp b/llvm/tools/obj2yaml/wasm2yaml.cpp
index 27398e5b00b..1bf8149493c 100644
--- a/llvm/tools/obj2yaml/wasm2yaml.cpp
+++ b/llvm/tools/obj2yaml/wasm2yaml.cpp
@@ -80,11 +80,15 @@ std::unique_ptr<WasmYAML::CustomSection> WasmDumper::dumpCustomSection(const Was
     for (const object::SymbolRef& Sym: Obj.symbols()) {
       const object::WasmSymbol Symbol = Obj.getWasmSymbol(Sym);
       if (Symbol.Flags != 0) {
-        WasmYAML::SymbolInfo Info = { Symbol.Name, Symbol.Flags };
-        LinkingSec->SymbolInfos.push_back(Info);
+        WasmYAML::SymbolInfo Info{Symbol.Name, Symbol.Flags};
+        LinkingSec->SymbolInfos.emplace_back(Info);
       }
     }
     LinkingSec->DataSize = Obj.linkingData().DataSize;
+    for (const wasm::WasmInitFunc &Func : Obj.linkingData().InitFunctions) {
+      WasmYAML::InitFunction F{Func.Priority, Func.FunctionIndex};
+      LinkingSec->InitFunctions.emplace_back(F);
+    }
     CustomSec = std::move(LinkingSec);
   } else {
     CustomSec = make_unique<WasmYAML::CustomSection>(WasmSec.Name);
diff --git a/llvm/tools/yaml2obj/yaml2wasm.cpp b/llvm/tools/yaml2obj/yaml2wasm.cpp
index 3eae8727b60..792f7c108bc 100644
--- a/llvm/tools/yaml2obj/yaml2wasm.cpp
+++ b/llvm/tools/yaml2obj/yaml2wasm.cpp
@@ -162,6 +162,17 @@ int WasmWriter::writeSectionContent(raw_ostream &OS, WasmYAML::LinkingSection &S
     }
     SubSection.Done();
   }
+
+  // INIT_FUNCS subsection
+  if (Section.InitFunctions.size()) {
+    encodeULEB128(wasm::WASM_INIT_FUNCS, OS);
+    encodeULEB128(Section.InitFunctions.size(), SubSection.GetStream());
+    for (const WasmYAML::InitFunction &Func : Section.InitFunctions) {
+      encodeULEB128(Func.Priority, SubSection.GetStream());
+      encodeULEB128(Func.FunctionIndex, SubSection.GetStream());
+    }
+    SubSection.Done();
+  }
   return 0;
 }