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

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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
This commit is contained in:
Sam Clegg 2021-09-28 11:43:47 -07:00
parent 0be9940ef2
commit 8fe128476e
3 changed files with 49 additions and 4 deletions
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45
lld/test/wasm/lto/tls.ll Normal file
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@ -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"
@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

4
lld/wasm/Driver.cpp
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@ -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();

4
lld/wasm/SymbolTable.cpp
View File

@ -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);