[PATCH] D96318: [lld][WebAssembly] Allow export for optional symbols

[Sam Clegg via Phabricator via llvm-commits]

sbc100 created this revision.
Herald added subscribers: wingo, ecnelises, sunfish, jgravelle-google, dschuff.
sbc100 requested review of this revision.
Herald added subscribers: llvm-commits, aheejin.
Herald added a project: LLVM.

This moves the error checking until after all optional
symbols (including the section start/end symbols) have
been created.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D96318

Files:
  lld/test/wasm/export-optional.s
  lld/wasm/Driver.cpp
  lld/wasm/SymbolTable.cpp
  lld/wasm/Writer.cpp


Index: lld/wasm/Writer.cpp
===================================================================
--- lld/wasm/Writer.cpp
+++ lld/wasm/Writer.cpp
@@ -1350,6 +1350,19 @@
       addStartStopSymbols(seg);
   }
 
+  // Delay reporting error about explict exports until after addStartStopSymbols
+  // which can create optional symbols.
+  for (auto &entry : config->exportedSymbols) {
+    StringRef name = entry.first();
+    Symbol *sym = symtab->find(name);
+    if (sym && sym->isDefined())
+      sym->forceExport = true;
+    else if (config->unresolvedSymbols == UnresolvedPolicy::ReportError)
+      error(Twine("symbol exported via --export not found: ") + name);
+    else if (config->unresolvedSymbols == UnresolvedPolicy::Warn)
+      warn(Twine("symbol exported via --export not found: ") + name);
+  }
+
   log("-- scanRelocations");
   scanRelocations();
   log("-- finalizeIndirectFunctionTable");
Index: lld/wasm/SymbolTable.cpp
===================================================================
--- lld/wasm/SymbolTable.cpp
+++ lld/wasm/SymbolTable.cpp
@@ -236,6 +236,8 @@
     return nullptr;
   LLVM_DEBUG(dbgs() << "addOptionalDataSymbol: " << name << "\n");
   auto *rtn = replaceSymbol<DefinedData>(s, name, WASM_SYMBOL_VISIBILITY_HIDDEN);
+  if (config->exportedSymbols.count(name))
+    rtn->forceExport = true;
   rtn->setVirtualAddress(value);
   rtn->referenced = true;
   return rtn;
Index: lld/wasm/Driver.cpp
===================================================================
--- lld/wasm/Driver.cpp
+++ lld/wasm/Driver.cpp
@@ -1015,11 +1015,6 @@
     Symbol *sym = symtab->find(arg->getValue());
     if (sym && sym->isDefined())
       sym->forceExport = true;
-    else if (config->unresolvedSymbols == UnresolvedPolicy::ReportError)
-      error(Twine("symbol exported via --export not found: ") +
-            arg->getValue());
-    else if (config->unresolvedSymbols == UnresolvedPolicy::Warn)
-      warn(Twine("symbol exported via --export not found: ") + arg->getValue());
   }
 
   if (!config->relocatable && !config->isPic) {
Index: lld/test/wasm/export-optional.s
===================================================================
--- /dev/null
+++ lld/test/wasm/export-optional.s
@@ -0,0 +1,31 @@
+# Test the --export of optional linker-synthetic symbols works.
+# Specifically the __start_xxx and __end_xx symbols.
+
+# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown %s -o %t.o
+# RUN: wasm-ld --export=__start_foo %t.o -o %t.wasm
+# RUN: obj2yaml %t.wasm | FileCheck %s
+
+  .globl  _start
+_start:
+  .functype _start () -> ()
+  i32.load foo
+  drop
+  end_function
+
+  .globl  foo
+  .section    foo,"",@
+foo:
+  .int32 42
+  .size foo, 4
+
+#      CHECK:  - Type:            EXPORT
+# CHECK-NEXT:    Exports:
+# CHECK-NEXT:      - Name:            memory
+# CHECK-NEXT:        Kind:            MEMORY
+# CHECK-NEXT:        Index:           0
+# CHECK-NEXT:      - Name:            _start
+# CHECK-NEXT:        Kind:            FUNCTION
+# CHECK-NEXT:        Index:           0
+# CHECK-NEXT:      - Name:            __start_foo
+# CHECK-NEXT:        Kind:            GLOBAL
+# CHECK-NEXT:        Index:           1


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