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[lld][WebAssembly] Add new __rodata_start/__rodata_end symbols #172102

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[lld][WebAssembly] Add new __rodata_start/__rodata_end symbols #172102

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20 changes: 13 additions & 7 deletions lld/test/wasm/export-all.s
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Original file line number Diff line number Diff line change
Expand Up @@ -34,24 +34,30 @@ foo:
# CHECK-NEXT: - Name: __data_end
# CHECK-NEXT: Kind: GLOBAL
# CHECK-NEXT: Index: 2
# CHECK-NEXT: - Name: __stack_low
# CHECK-NEXT: - Name: __rodata_start
# CHECK-NEXT: Kind: GLOBAL
# CHECK-NEXT: Index: 3
# CHECK-NEXT: - Name: __stack_high
# CHECK-NEXT: - Name: __rodata_end
# CHECK-NEXT: Kind: GLOBAL
# CHECK-NEXT: Index: 4
# CHECK-NEXT: - Name: __global_base
# CHECK-NEXT: - Name: __stack_low
# CHECK-NEXT: Kind: GLOBAL
# CHECK-NEXT: Index: 5
# CHECK-NEXT: - Name: __heap_base
# CHECK-NEXT: - Name: __stack_high
# CHECK-NEXT: Kind: GLOBAL
# CHECK-NEXT: Index: 6
# CHECK-NEXT: - Name: __heap_end
# CHECK-NEXT: - Name: __global_base
# CHECK-NEXT: Kind: GLOBAL
# CHECK-NEXT: Index: 7
# CHECK-NEXT: - Name: __memory_base
# CHECK-NEXT: - Name: __heap_base
# CHECK-NEXT: Kind: GLOBAL
# CHECK-NEXT: Index: 8
# CHECK-NEXT: - Name: __table_base
# CHECK-NEXT: - Name: __heap_end
# CHECK-NEXT: Kind: GLOBAL
# CHECK-NEXT: Index: 9
# CHECK-NEXT: - Name: __memory_base
# CHECK-NEXT: Kind: GLOBAL
# CHECK-NEXT: Index: 10
# CHECK-NEXT: - Name: __table_base
# CHECK-NEXT: Kind: GLOBAL
# CHECK-NEXT: Index: 11
22 changes: 14 additions & 8 deletions lld/test/wasm/mutable-global-exports.s
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Original file line number Diff line number Diff line change
Expand Up @@ -91,30 +91,36 @@ _start:
# CHECK-ALL-NEXT: - Name: __data_end
# CHECK-ALL-NEXT: Kind: GLOBAL
# CHECK-ALL-NEXT: Index: 4
# CHECK-ALL-NEXT: - Name: __stack_low
# CHECK-ALL-NEXT: - Name: __rodata_start
# CHECK-ALL-NEXT: Kind: GLOBAL
# CHECK-ALL-NEXT: Index: 5
# CHECK-ALL-NEXT: - Name: __stack_high
# CHECK-ALL-NEXT: - Name: __rodata_end
# CHECK-ALL-NEXT: Kind: GLOBAL
# CHECK-ALL-NEXT: Index: 6
# CHECK-ALL-NEXT: - Name: __global_base
# CHECK-ALL-NEXT: - Name: __stack_low
# CHECK-ALL-NEXT: Kind: GLOBAL
# CHECK-ALL-NEXT: Index: 7
# CHECK-ALL-NEXT: - Name: __heap_base
# CHECK-ALL-NEXT: - Name: __stack_high
# CHECK-ALL-NEXT: Kind: GLOBAL
# CHECK-ALL-NEXT: Index: 8
# CHECK-ALL-NEXT: - Name: __heap_end
# CHECK-ALL-NEXT: - Name: __global_base
# CHECK-ALL-NEXT: Kind: GLOBAL
# CHECK-ALL-NEXT: Index: 9
# CHECK-ALL-NEXT: - Name: __memory_base
# CHECK-ALL-NEXT: - Name: __heap_base
# CHECK-ALL-NEXT: Kind: GLOBAL
# CHECK-ALL-NEXT: Index: 10
# CHECK-ALL-NEXT: - Name: __table_base
# CHECK-ALL-NEXT: - Name: __heap_end
# CHECK-ALL-NEXT: Kind: GLOBAL
# CHECK-ALL-NEXT: Index: 11
# CHECK-ALL-NEXT: - Name: __wasm_first_page_end
# CHECK-ALL-NEXT: - Name: __memory_base
# CHECK-ALL-NEXT: Kind: GLOBAL
# CHECK-ALL-NEXT: Index: 12
# CHECK-ALL-NEXT: - Name: __table_base
# CHECK-ALL-NEXT: Kind: GLOBAL
# CHECK-ALL-NEXT: Index: 13
# CHECK-ALL-NEXT: - Name: __wasm_first_page_end
# CHECK-ALL-NEXT: Kind: GLOBAL
# CHECK-ALL-NEXT: Index: 14
# CHECK-ALL-NEXT: - Type: CODE

# CHECK-ALL: Name: target_features
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5 changes: 5 additions & 0 deletions lld/wasm/Config.h
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Original file line number Diff line number Diff line change
Expand Up @@ -173,6 +173,11 @@ struct Ctx {
// Symbol whose value is the alignment of the TLS block.
GlobalSymbol *tlsAlign;

// __rodata_start/__rodata_end
// Symbols marking the start/end of readonly data
DefinedData *rodataStart;
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@dschuff dschuff Dec 12, 2025

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Kind of unfortunate that we have __stack_low, __heap_base, and __rodata_start. But I guess it's too late to fix the inconsistency.

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@sbc100 sbc100 Dec 13, 2025

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Hmm.. that is kind of sad/absurd I agree :)

DefinedData *rodataEnd;

// __data_end
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@dschuff dschuff Dec 12, 2025

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Any particular reason why __data_start doesn't exist?

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@sbc100 sbc100 Dec 13, 2025

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Just historical need I believe.

// Symbol marking the end of the data and bss.
DefinedData *dataEnd;
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5 changes: 4 additions & 1 deletion lld/wasm/Driver.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -988,8 +988,11 @@ static void createOptionalSymbols() {

ctx.sym.dsoHandle = symtab->addOptionalDataSymbol("__dso_handle");

if (!ctx.arg.shared)
if (!ctx.arg.shared) {
ctx.sym.dataEnd = symtab->addOptionalDataSymbol("__data_end");
ctx.sym.rodataStart = symtab->addOptionalDataSymbol("__rodata_start");
ctx.sym.rodataEnd = symtab->addOptionalDataSymbol("__rodata_end");
}

if (!ctx.isPic) {
ctx.sym.stackLow = symtab->addOptionalDataSymbol("__stack_low");
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8 changes: 8 additions & 0 deletions lld/wasm/Writer.cpp
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Expand Up @@ -401,7 +401,15 @@ void Writer::layoutMemory() {
}
}

if (ctx.sym.rodataStart && seg->name.starts_with(".rodata") &&
!ctx.sym.rodataStart->getVA())
ctx.sym.rodataStart->setVA(memoryPtr);

memoryPtr += seg->size;

// Might get set more than once if segment merging is not enabled.
if (ctx.sym.rodataEnd && seg->name.starts_with(".rodata"))
ctx.sym.rodataEnd->setVA(memoryPtr);
}

// Make space for the memory initialization flag
Expand Down