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[WebAssembly] Implement the .reloc directive for WASM #146952

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[WebAssembly] Implement the .reloc directive for WASM #146952

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f44dcf6
Add a test
SingleAccretion Jul 3, 2025
1e75b9b
Implement the .reloc directive for WASM
SingleAccretion Jul 3, 2025
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8 changes: 6 additions & 2 deletions llvm/lib/MC/WasmObjectWriter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -530,8 +530,12 @@ void WasmObjectWriter::recordRelocation(const MCFragment &F,
// be negative and don't wrap.
FixedValue = 0;

unsigned Type =
TargetObjectWriter->getRelocType(Target, Fixup, FixupSection, IsLocRel);
unsigned Type;
if (mc::isRelocRelocation(Fixup.getKind()))
Type = Fixup.getKind() - FirstLiteralRelocationKind;
else
Type =
TargetObjectWriter->getRelocType(Target, Fixup, FixupSection, IsLocRel);

// Absolute offset within a section or a function.
// Currently only supported for metadata sections.
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19 changes: 19 additions & 0 deletions llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyAsmBackend.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@

#include "MCTargetDesc/WebAssemblyFixupKinds.h"
#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCExpr.h"
Expand All @@ -36,6 +37,7 @@ class WebAssemblyAsmBackend final : public MCAsmBackend {
: MCAsmBackend(llvm::endianness::little), Is64Bit(Is64Bit),
IsEmscripten(IsEmscripten) {}

std::optional<MCFixupKind> getFixupKind(StringRef Name) const override;
MCFixupKindInfo getFixupKindInfo(MCFixupKind Kind) const override;

void applyFixup(const MCFragment &, const MCFixup &, const MCValue &Target,
Expand All @@ -48,6 +50,18 @@ class WebAssemblyAsmBackend final : public MCAsmBackend {
const MCSubtargetInfo *STI) const override;
};

std::optional<MCFixupKind>
WebAssemblyAsmBackend::getFixupKind(StringRef Name) const {
unsigned Type = llvm::StringSwitch<unsigned>(Name)
#define WASM_RELOC(NAME, ID) .Case(#NAME, ID)
#include "llvm/BinaryFormat/WasmRelocs.def"
#undef WASM_RELOC
.Default(-1u);
if (Type != -1u)
return static_cast<MCFixupKind>(FirstLiteralRelocationKind + Type);
return std::nullopt;
}

MCFixupKindInfo
WebAssemblyAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
const static MCFixupKindInfo Infos[WebAssembly::NumTargetFixupKinds] = {
Expand All @@ -61,6 +75,11 @@ WebAssemblyAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
{"fixup_uleb128_i64", 0, 10 * 8, 0},
};

// Fixup kinds from raw relocation types and .reloc directives force
// relocations and do not use these fields.
if (mc::isRelocation(Kind))
return MCAsmBackend::getFixupKindInfo(FK_NONE);

if (Kind < FirstTargetFixupKind)
return MCAsmBackend::getFixupKindInfo(Kind);

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29 changes: 29 additions & 0 deletions llvm/test/MC/WebAssembly/reloc-directive.s
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@@ -0,0 +1,29 @@
# RUN: llvm-mc -triple=wasm32 %s | FileCheck --check-prefix=PRINT %s
# RUN: llvm-mc -filetype=obj -triple=wasm32 %s | llvm-readobj -r - | FileCheck %s

load_function_index_func:
.functype load_function_index_func () -> (i32)
i32.const 0
nop
nop
nop
nop
i32.load 0
end_function

# PRINT: .reloc load_function_index_func+2, R_WASM_MEMORY_ADDR_SLEB, function_index_data+1
# CHECK: Section ({{.*}}) CODE {
# CHECK-NEXT: 0x4 R_WASM_MEMORY_ADDR_SLEB function_index_data 1
# CHECK-NEXT: }
.reloc load_function_index_func + 2, R_WASM_MEMORY_ADDR_SLEB, function_index_data + 1

.section .data,"",@
function_index_data:
.int32 0
.size function_index_data, 4

# PRINT: .reloc function_index_data, R_WASM_FUNCTION_INDEX_I32, load_function_index_func
# CHECK: Section ({{.*}}) DATA {
# CHECK-NEXT: 0x6 R_WASM_FUNCTION_INDEX_I32 load_function_index_func
# CHECK-NEXT: }
.reloc function_index_data, R_WASM_FUNCTION_INDEX_I32, load_function_index_func
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