[lld] 34d033c - [lld][WebAssembly] Allow --export of optional start/stop symbols

[Sam Clegg via llvm-commits]

Author: Sam Clegg
Date: 2021-02-09T13:14:52-08:00
New Revision: 34d033ca129fdb1507427d45f518fdb523847732

URL: https://github.com/llvm/llvm-project/commit/34d033ca129fdb1507427d45f518fdb523847732
DIFF: https://github.com/llvm/llvm-project/commit/34d033ca129fdb1507427d45f518fdb523847732.diff

LOG: [lld][WebAssembly] Allow --export of optional start/stop symbols

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

Differential Revision: https://reviews.llvm.org/D96318

Added: 
    lld/test/wasm/export-optional.s

Modified: 
    lld/wasm/Driver.cpp
    lld/wasm/Writer.cpp

Removed: 
    


################################################################################
diff  --git a/lld/test/wasm/export-optional.s b/lld/test/wasm/export-optional.s
new file mode 100644
index 000000000000..7e6f4debc0a9
--- /dev/null
+++ b/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

diff  --git a/lld/wasm/Driver.cpp b/lld/wasm/Driver.cpp
index 5927d1b53e7d..4cd529686e4d 100644
--- a/lld/wasm/Driver.cpp
+++ b/lld/wasm/Driver.cpp
@@ -1015,11 +1015,6 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
     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) {

diff  --git a/lld/wasm/Writer.cpp b/lld/wasm/Writer.cpp
index 1587e97b5b2d..aeafc330e103 100644
--- a/lld/wasm/Writer.cpp
+++ b/lld/wasm/Writer.cpp
@@ -1350,6 +1350,19 @@ void Writer::run() {
       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");