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[lld][WebAssembly] Do not relocate ABSOLUTE symbols #153763

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Merged
merged 4 commits into from
Aug 19, 2025
Merged

[lld][WebAssembly] Do not relocate ABSOLUTE symbols #153763

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3f65a78
[lld][WebAssembly] Do not relocate ABSOLUTE symbols
yamt Aug 15, 2025
7cdff15
add a test
yamt Aug 18, 2025
08fde96
check ABSOLUTE before TLS
yamt Aug 18, 2025
7c137aa
lld/test/wasm/pie.s: simplify a bit
yamt Aug 19, 2025
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27 changes: 24 additions & 3 deletions lld/test/wasm/pie.s
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@
# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-emscripten %S/Inputs/internal_func.s -o %t.internal_func.o
# RUN: wasm-ld --no-gc-sections --experimental-pic -pie --unresolved-symbols=import-dynamic -o %t.wasm %t.o %t.internal_func.o
# RUN: obj2yaml %t.wasm | FileCheck %s
# RUN: llvm-objdump --disassemble-symbols=__wasm_call_ctors,__wasm_apply_data_relocs --no-show-raw-insn --no-leading-addr %t.wasm | FileCheck %s --check-prefixes DISASSEM
# RUN: llvm-objdump --disassemble-symbols=__wasm_call_ctors,__wasm_apply_data_relocs,__wasm_apply_global_relocs --no-show-raw-insn --no-leading-addr %t.wasm | FileCheck %s --check-prefixes DISASSEM

.functype external_func () -> ()
.functype internal_func1 () -> (i32)
Expand Down Expand Up @@ -41,6 +41,9 @@ foo:
drop

global.get __stack_pointer
drop

global.get __wasm_first_page_end@GOT
end_function

get_data_address:
Expand Down Expand Up @@ -145,6 +148,18 @@ _start:
# DISASSEM-LABEL: <__wasm_apply_data_relocs>:
# DISASSEM: end

# global 6 is __wasm_first_page_end, which is ABSOLUTE and
# thus should not be relocated.
#
# DISASSEM-LABEL: <__wasm_apply_global_relocs>:
# DISASSEM: global.set 4
# DISASSEM: global.set 5
# DISASSEM-NOT: global.set 6
# DISASSEM: global.set 7
# DISASSEM: global.set 8
# DISASSEM: global.set 9
# DISASSEM: end

# Run the same test with extended-const support. When this is available
# we don't need __wasm_apply_global_relocs and instead rely on the add
# instruction in the InitExpr. We also, therefore, do not need these globals
Expand Down Expand Up @@ -173,17 +188,23 @@ _start:
# EXTENDED-CONST-NEXT: Type: I32
# EXTENDED-CONST-NEXT: Mutable: false
# EXTENDED-CONST-NEXT: InitExpr:
# EXTENDED-CONST-NEXT: Opcode: I32_CONST
# EXTENDED-CONST-NEXT: Value: 65536
# EXTENDED-CONST-NEXT: - Index: 7
# EXTENDED-CONST-NEXT: Type: I32
# EXTENDED-CONST-NEXT: Mutable: false
# EXTENDED-CONST-NEXT: InitExpr:
# EXTENDED-CONST-NEXT: Extended: true
# This instruction sequence decodes to:
# (global.get[0x23] 0x1 i32.const[0x41] 0x0C i32.add[0x6A] end[0x0b])
# EXTENDED-CONST-NEXT: Body: 2301410C6A0B
# EXTENDED-CONST-NEXT: - Index: 7
# EXTENDED-CONST-NEXT: - Index: 8
# EXTENDED-CONST-NEXT: Type: I32
# EXTENDED-CONST-NEXT: Mutable: false
# EXTENDED-CONST-NEXT: InitExpr:
# EXTENDED-CONST-NEXT: Opcode: GLOBAL_GET
# EXTENDED-CONST-NEXT: Index: 2
# EXTENDED-CONST-NEXT: - Index: 8
# EXTENDED-CONST-NEXT: - Index: 9
# EXTENDED-CONST-NEXT: Type: I32
# EXTENDED-CONST-NEXT: Mutable: false
# EXTENDED-CONST-NEXT: InitExpr:
Expand Down
5 changes: 4 additions & 1 deletion lld/wasm/SyntheticSections.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -440,6 +440,8 @@ void GlobalSection::generateRelocationCode(raw_ostream &os, bool TLS) const {
: WASM_OPCODE_I32_ADD;

for (const Symbol *sym : internalGotSymbols) {
if (sym->flags & WASM_SYMBOL_ABSOLUTE)
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Maybe do this 2 lines up before the TLS check?

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why? just because it can be slightly cheaper?

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done

continue;
if (TLS != sym->isTLS())
continue;

Expand Down Expand Up @@ -503,7 +505,8 @@ void GlobalSection::writeBody() {
bool useExtendedConst = false;
uint32_t globalIdx;
int64_t offset;
if (ctx.arg.extendedConst && ctx.isPic) {
if (ctx.arg.extendedConst && ctx.isPic &&
(sym->flags & WASM_SYMBOL_ABSOLUTE) == 0) {
if (auto *d = dyn_cast<DefinedData>(sym)) {
if (!sym->isTLS()) {
globalIdx = ctx.sym.memoryBase->getGlobalIndex();
Expand Down