[lld] 8fe1284 - [lld][WebAssembly] Create optional internal symbols only after LTO object as been added

[Sam Clegg via llvm-commits]

Author: Sam Clegg
Date: 2021-10-05T13:31:09-07:00
New Revision: 8fe128476eb85ba582c477f61bc8ed003dd04f03

URL: https://github.com/llvm/llvm-project/commit/8fe128476eb85ba582c477f61bc8ed003dd04f03
DIFF: https://github.com/llvm/llvm-project/commit/8fe128476eb85ba582c477f61bc8ed003dd04f03.diff

LOG: [lld][WebAssembly] Create optional internal symbols only after LTO object as been added

This is important for the cases where new symbols can be introduced
during LTO.   Specifically this happens for during TLS-lowering where
references to `__tls_base` can be introduced.

Fixes: https://github.com/emscripten-core/emscripten/issues/12489

Differential Revision: https://reviews.llvm.org/D111171

Added: 
    lld/test/wasm/lto/tls.ll

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

Removed: 
    


################################################################################
diff  --git a/lld/test/wasm/lto/tls.ll b/lld/test/wasm/lto/tls.ll
new file mode 100644
index 0000000000000..8d6185e727404
--- /dev/null
+++ b/lld/test/wasm/lto/tls.ll
@@ -0,0 +1,45 @@
+; Test that LTO objects build with TLS and threading support can be linked into
+; a single threaded binary.  Specifically the references to `__tls_base` that
+; can be generated at LTO-time need to trigger the creation of the internal/fake
+; `__tls_base` symbol in the linker.
+
+; RUN: llvm-as %s -o %t1.o
+; RUN: wasm-ld --export=tls_int --export=get_tls %t1.o -o %t
+; RUN: obj2yaml %t | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-i64:64-f128:64-n32:64-S128-ni:1:10:20"
+target triple = "wasm32-unknown-emscripten"
+
+ at tls_int = dso_local thread_local global i32 99
+
+define i32 @get_tls() #0 {
+  %val = load i32, i32* @tls_int
+  ret i32 %val
+}
+
+define void @_start() #0 {
+  ret void
+}
+
+attributes #0 = { noinline nounwind optnone "target-features"="+atomics,+bulk-memory,+mutable-globals,+sign-ext" }
+
+;      CHECK:   - Type:            GLOBAL
+; CHECK-NEXT:     Globals:
+; CHECK-NEXT:       - Index:           0
+; CHECK-NEXT:         Type:            I32
+; CHECK-NEXT:         Mutable:         true
+; CHECK-NEXT:         InitExpr:
+; CHECK-NEXT:           Opcode:          I32_CONST
+; CHECK-NEXT:           Value:           66576
+; CHECK-NEXT:       - Index:           1
+; CHECK-NEXT:         Type:            I32
+; CHECK-NEXT:         Mutable:         false
+; CHECK-NEXT:         InitExpr:
+; CHECK-NEXT:           Opcode:          I32_CONST
+; CHECK-NEXT:           Value:           1024
+
+;      CHECK:     GlobalNames:
+; CHECK-NEXT:       - Index:           0
+; CHECK-NEXT:         Name:            __stack_pointer
+; CHECK-NEXT:       - Index:           1
+; CHECK-NEXT:         Name:            __tls_base

diff  --git a/lld/wasm/Driver.cpp b/lld/wasm/Driver.cpp
index 9285baab96420..4f7423c06e832 100644
--- a/lld/wasm/Driver.cpp
+++ b/lld/wasm/Driver.cpp
@@ -947,8 +947,6 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
     }
   }
 
-  createOptionalSymbols();
-
   if (errorCount())
     return;
 
@@ -976,6 +974,8 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
   if (errorCount())
     return;
 
+  createOptionalSymbols();
+
   // Resolve any variant symbols that were created due to signature
   // mismatchs.
   symtab->handleSymbolVariants();

diff  --git a/lld/wasm/SymbolTable.cpp b/lld/wasm/SymbolTable.cpp
index 89fb481d72ceb..a0e59e2eb8e60 100644
--- a/lld/wasm/SymbolTable.cpp
+++ b/lld/wasm/SymbolTable.cpp
@@ -258,11 +258,11 @@ DefinedGlobal *SymbolTable::addSyntheticGlobal(StringRef name, uint32_t flags,
 
 DefinedGlobal *SymbolTable::addOptionalGlobalSymbol(StringRef name,
                                                     InputGlobal *global) {
-  LLVM_DEBUG(dbgs() << "addOptionalGlobalSymbol: " << name << " -> " << global
-                    << "\n");
   Symbol *s = find(name);
   if (!s || s->isDefined())
     return nullptr;
+  LLVM_DEBUG(dbgs() << "addOptionalGlobalSymbol: " << name << " -> " << global
+                    << "\n");
   syntheticGlobals.emplace_back(global);
   return replaceSymbol<DefinedGlobal>(s, name, WASM_SYMBOL_VISIBILITY_HIDDEN,
                                       nullptr, global);