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Merged
tru merged 2 commits into from
Dec 17, 2024
Merged

release/19.x: [WebAssembly] Handle symbols in .init_array sections (#119127) #119533

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8069ce6
[WebAssembly] Support multiple `.init_array` fragments when writing W…
georgestagg Dec 4, 2024
8e9465b
[WebAssembly] Handle symbols in `.init_array` sections (#119127)
georgestagg Dec 10, 2024
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111 changes: 67 additions & 44 deletions llvm/lib/MC/WasmObjectWriter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1326,6 +1326,22 @@ static bool isInSymtab(const MCSymbolWasm &Sym) {
return true;
}

static bool isSectionReferenced(MCAssembler &Asm, MCSectionWasm &Section) {
StringRef SectionName = Section.getName();

for (const MCSymbol &S : Asm.symbols()) {
const auto &WS = static_cast<const MCSymbolWasm &>(S);
if (WS.isData() && WS.isInSection()) {
auto &RefSection = static_cast<MCSectionWasm &>(WS.getSection());
if (RefSection.getName() == SectionName) {
return true;
}
}
}

return false;
}

void WasmObjectWriter::prepareImports(
SmallVectorImpl<wasm::WasmImport> &Imports, MCAssembler &Asm) {
// For now, always emit the memory import, since loads and stores are not
Expand Down Expand Up @@ -1482,8 +1498,10 @@ uint64_t WasmObjectWriter::writeOneObject(MCAssembler &Asm,
LLVM_DEBUG(dbgs() << "Processing Section " << SectionName << " group "
<< Section.getGroup() << "\n";);

// .init_array sections are handled specially elsewhere.
if (SectionName.starts_with(".init_array"))
// .init_array sections are handled specially elsewhere, include them in
// data segments if and only if referenced by a symbol.
if (SectionName.starts_with(".init_array") &&
!isSectionReferenced(Asm, Section))
continue;

// Code is handled separately
Expand Down Expand Up @@ -1853,49 +1871,54 @@ uint64_t WasmObjectWriter::writeOneObject(MCAssembler &Asm,
if (EmptyFrag.getKind() != MCFragment::FT_Data)
report_fatal_error(".init_array section should be aligned");

const MCFragment &AlignFrag = *EmptyFrag.getNext();
if (AlignFrag.getKind() != MCFragment::FT_Align)
report_fatal_error(".init_array section should be aligned");
if (cast<MCAlignFragment>(AlignFrag).getAlignment() !=
Align(is64Bit() ? 8 : 4))
report_fatal_error(".init_array section should be aligned for pointers");

const MCFragment &Frag = *AlignFrag.getNext();
if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data)
report_fatal_error("only data supported in .init_array section");

uint16_t Priority = UINT16_MAX;
unsigned PrefixLength = strlen(".init_array");
if (WS.getName().size() > PrefixLength) {
if (WS.getName()[PrefixLength] != '.')
const MCFragment *nextFrag = EmptyFrag.getNext();
while (nextFrag != nullptr) {
const MCFragment &AlignFrag = *nextFrag;
if (AlignFrag.getKind() != MCFragment::FT_Align)
report_fatal_error(".init_array section should be aligned");
if (cast<MCAlignFragment>(AlignFrag).getAlignment() !=
Align(is64Bit() ? 8 : 4))
report_fatal_error(
".init_array section priority should start with '.'");
if (WS.getName().substr(PrefixLength + 1).getAsInteger(10, Priority))
report_fatal_error("invalid .init_array section priority");
}
const auto &DataFrag = cast<MCDataFragment>(Frag);
const SmallVectorImpl<char> &Contents = DataFrag.getContents();
for (const uint8_t *
P = (const uint8_t *)Contents.data(),
*End = (const uint8_t *)Contents.data() + Contents.size();
P != End; ++P) {
if (*P != 0)
report_fatal_error("non-symbolic data in .init_array section");
}
for (const MCFixup &Fixup : DataFrag.getFixups()) {
assert(Fixup.getKind() ==
MCFixup::getKindForSize(is64Bit() ? 8 : 4, false));
const MCExpr *Expr = Fixup.getValue();
auto *SymRef = dyn_cast<MCSymbolRefExpr>(Expr);
if (!SymRef)
report_fatal_error("fixups in .init_array should be symbol references");
const auto &TargetSym = cast<const MCSymbolWasm>(SymRef->getSymbol());
if (TargetSym.getIndex() == InvalidIndex)
report_fatal_error("symbols in .init_array should exist in symtab");
if (!TargetSym.isFunction())
report_fatal_error("symbols in .init_array should be for functions");
InitFuncs.push_back(
std::make_pair(Priority, TargetSym.getIndex()));
".init_array section should be aligned for pointers");

const MCFragment &Frag = *AlignFrag.getNext();
nextFrag = Frag.getNext();
if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data)
report_fatal_error("only data supported in .init_array section");

uint16_t Priority = UINT16_MAX;
unsigned PrefixLength = strlen(".init_array");
if (WS.getName().size() > PrefixLength) {
if (WS.getName()[PrefixLength] != '.')
report_fatal_error(
".init_array section priority should start with '.'");
if (WS.getName().substr(PrefixLength + 1).getAsInteger(10, Priority))
report_fatal_error("invalid .init_array section priority");
}
const auto &DataFrag = cast<MCDataFragment>(Frag);
const SmallVectorImpl<char> &Contents = DataFrag.getContents();
for (const uint8_t *
P = (const uint8_t *)Contents.data(),
*End = (const uint8_t *)Contents.data() + Contents.size();
P != End; ++P) {
if (*P != 0)
report_fatal_error("non-symbolic data in .init_array section");
}
for (const MCFixup &Fixup : DataFrag.getFixups()) {
assert(Fixup.getKind() ==
MCFixup::getKindForSize(is64Bit() ? 8 : 4, false));
const MCExpr *Expr = Fixup.getValue();
auto *SymRef = dyn_cast<MCSymbolRefExpr>(Expr);
if (!SymRef)
report_fatal_error(
"fixups in .init_array should be symbol references");
const auto &TargetSym = cast<const MCSymbolWasm>(SymRef->getSymbol());
if (TargetSym.getIndex() == InvalidIndex)
report_fatal_error("symbols in .init_array should exist in symtab");
if (!TargetSym.isFunction())
report_fatal_error("symbols in .init_array should be for functions");
InitFuncs.push_back(std::make_pair(Priority, TargetSym.getIndex()));
}
}
}

Expand Down
91 changes: 91 additions & 0 deletions llvm/test/MC/WebAssembly/init-array-label.s
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Original file line number Diff line number Diff line change
@@ -0,0 +1,91 @@
# RUN: llvm-mc -triple=wasm32-unknown-unknown -filetype=obj < %s | obj2yaml | FileCheck %s

init1:
.functype init1 () -> ()
end_function

init2:
.functype init2 () -> ()
end_function

.section .init_array.42,"",@
.p2align 2, 0x0
.int32 init1

.section .init_array,"",@
.globl p_init1
.p2align 2, 0x0
p_init1:
.int32 init1
.size p_init1, 4

.section .init_array,"",@
.globl p_init2
.p2align 2, 0x0
p_init2:
.int32 init1
.int32 init2
.size p_init2, 8

# CHECK: - Type: FUNCTION
# CHECK-NEXT: FunctionTypes: [ 0, 0 ]
# CHECK-NEXT: - Type: DATACOUNT
# CHECK-NEXT: Count: 1
# CHECK-NEXT: - Type: CODE
# CHECK-NEXT: Functions:
# CHECK-NEXT: - Index: 0
# CHECK-NEXT: Locals: []
# CHECK-NEXT: Body: 0B
# CHECK-NEXT: - Index: 1
# CHECK-NEXT: Locals: []
# CHECK-NEXT: Body: 0B
# CHECK-NEXT: - Type: DATA
# CHECK-NEXT: Segments:
# CHECK-NEXT: - SectionOffset: 6
# CHECK-NEXT: InitFlags: 0
# CHECK-NEXT: Offset:
# CHECK-NEXT: Opcode: I32_CONST
# CHECK-NEXT: Value: 0
# CHECK-NEXT: Content: '000000000000000000000000'
# CHECK-NEXT: - Type: CUSTOM
# CHECK-NEXT: Name: linking
# CHECK-NEXT: Version: 2
# CHECK-NEXT: SymbolTable:
# CHECK-NEXT: - Index: 0
# CHECK-NEXT: Kind: FUNCTION
# CHECK-NEXT: Name: init1
# CHECK-NEXT: Flags: [ BINDING_LOCAL ]
# CHECK-NEXT: Function: 0
# CHECK-NEXT: - Index: 1
# CHECK-NEXT: Kind: FUNCTION
# CHECK-NEXT: Name: init2
# CHECK-NEXT: Flags: [ BINDING_LOCAL ]
# CHECK-NEXT: Function: 1
# CHECK-NEXT: - Index: 2
# CHECK-NEXT: Kind: DATA
# CHECK-NEXT: Name: p_init1
# CHECK-NEXT: Flags: [ ]
# CHECK-NEXT: Segment: 0
# CHECK-NEXT: Size: 4
# CHECK-NEXT: - Index: 3
# CHECK-NEXT: Kind: DATA
# CHECK-NEXT: Name: p_init2
# CHECK-NEXT: Flags: [ ]
# CHECK-NEXT: Segment: 0
# CHECK-NEXT: Offset: 4
# CHECK-NEXT: Size: 8
# CHECK-NEXT: SegmentInfo:
# CHECK-NEXT: - Index: 0
# CHECK-NEXT: Name: .init_array
# CHECK-NEXT: Alignment: 2
# CHECK-NEXT: Flags: [ ]
# CHECK-NEXT: InitFunctions:
# CHECK-NEXT: - Priority: 42
# CHECK-NEXT: Symbol: 0
# CHECK-NEXT: - Priority: 65535
# CHECK-NEXT: Symbol: 0
# CHECK-NEXT: - Priority: 65535
# CHECK-NEXT: Symbol: 0
# CHECK-NEXT: - Priority: 65535
# CHECK-NEXT: Symbol: 1
# CHECK-NEXT: ...
49 changes: 49 additions & 0 deletions llvm/test/MC/WebAssembly/init-array.s
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Original file line number Diff line number Diff line change
@@ -0,0 +1,49 @@
# RUN: llvm-mc -triple=wasm32-unknown-unknown -filetype=obj < %s | obj2yaml | FileCheck %s

init1:
.functype init1 () -> ()
end_function

init2:
.functype init2 () -> ()
end_function

.section .init_array,"",@
.p2align 2, 0
.int32 init1

.section .init_array,"",@
.p2align 2
.int32 init2

# CHECK: - Type: FUNCTION
# CHECK-NEXT: FunctionTypes: [ 0, 0 ]
# CHECK-NEXT: - Type: CODE
# CHECK-NEXT: Functions:
# CHECK-NEXT: - Index: 0
# CHECK-NEXT: Locals: []
# CHECK-NEXT: Body: 0B
# CHECK-NEXT: - Index: 1
# CHECK-NEXT: Locals: []
# CHECK-NEXT: Body: 0B
# CHECK-NEXT: - Type: CUSTOM
# CHECK-NEXT: Name: linking
# CHECK-NEXT: Version: 2
# CHECK-NEXT: SymbolTable:
# CHECK-NEXT: - Index: 0
# CHECK-NEXT: Kind: FUNCTION
# CHECK-NEXT: Name: init1
# CHECK-NEXT: Flags: [ BINDING_LOCAL ]
# CHECK-NEXT: Function: 0
# CHECK-NEXT: - Index: 1
# CHECK-NEXT: Kind: FUNCTION
# CHECK-NEXT: Name: init2
# CHECK-NEXT: Flags: [ BINDING_LOCAL ]
# CHECK-NEXT: Function: 1
# CHECK-NEXT: InitFunctions:
# CHECK-NEXT: - Priority: 65535
# CHECK-NEXT: Symbol: 0
# CHECK-NEXT: - Priority: 65535
# CHECK-NEXT: Symbol: 1
# CHECK-NEXT: ...
#
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