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[6.2][Legacy Driver][wasm] Pass --table-base to reserve low function addresses #84286

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Merged
merged 2 commits into from
Sep 16, 2025
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[6.2][Legacy Driver][wasm] Pass --table-base to reserve low function addresses #84286

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908b7b5
[NFC][wasm] Fix incorrect comment about reserved low addresses
kateinoigakukun Sep 15, 2025
d8ae012
[Legacy Driver][wasm] Pass `--table-base` to reserve low function add…
kateinoigakukun Sep 15, 2025
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8 changes: 6 additions & 2 deletions lib/Driver/WebAssemblyToolChains.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -188,12 +188,16 @@ toolchains::WebAssembly::constructInvocation(const DynamicLinkJobAction &job,

// WebAssembly doesn't reserve low addresses But without "extra inhabitants"
// of the pointer representation, runtime performance and memory footprint are
// worse. So assume that compiler driver uses wasm-ld and --global-base=1024
// to reserve low 1KB.
// worse. So assume that compiler driver uses wasm-ld and --global-base=4096
// to reserve low 4KB.
Arguments.push_back("-Xlinker");
Arguments.push_back(context.Args.MakeArgString(
Twine("--global-base=") +
std::to_string(SWIFT_ABI_WASM32_LEAST_VALID_POINTER)));
Arguments.push_back("-Xlinker");
Arguments.push_back(context.Args.MakeArgString(
Twine("--table-base=") +
std::to_string(SWIFT_ABI_WASM32_LEAST_VALID_POINTER)));

// These custom arguments should be right before the object file at the end.
context.Args.AddAllArgs(Arguments, options::OPT_linker_option_Group);
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4 changes: 2 additions & 2 deletions stdlib/public/SwiftShims/swift/shims/System.h
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Expand Up @@ -220,8 +220,8 @@

// WebAssembly doesn't reserve low addresses. But without "extra inhabitants" of
// the pointer representation, runtime performance and memory footprint are
// worse. So assume that compiler driver uses wasm-ld and --global-base=1024 to
// reserve low 1KB.
// worse. So assume that compiler driver uses wasm-ld and --global-base=4096 to
// reserve low 4KB.
#define SWIFT_ABI_WASM32_LEAST_VALID_POINTER 4096

#endif // SWIFT_STDLIB_SHIMS_ABI_SYSTEM_H