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rustc: Place wasm linker args first instead of last #57337

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Jan 13, 2019
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rustc: Place wasm linker args first instead of last #57337

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122 changes: 62 additions & 60 deletions src/librustc_codegen_ssa/back/linker.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -81,11 +81,7 @@ impl LinkerInfo {
}

LinkerFlavor::Lld(LldFlavor::Wasm) => {
Box::new(WasmLd {
cmd,
sess,
info: self
}) as Box<dyn Linker>
Box::new(WasmLd::new(cmd, sess, self)) as Box<dyn Linker>
}
}
}
Expand Down Expand Up @@ -876,6 +872,67 @@ pub struct WasmLd<'a> {
info: &'a LinkerInfo,
}

impl<'a> WasmLd<'a> {
fn new(mut cmd: Command, sess: &'a Session, info: &'a LinkerInfo) -> WasmLd<'a> {
// There have been reports in the wild (rustwasm/wasm-bindgen#119) of
// using threads causing weird hangs and bugs. Disable it entirely as
// this isn't yet the bottleneck of compilation at all anyway.
cmd.arg("--no-threads");

// By default LLD only gives us one page of stack (64k) which is a
// little small. Default to a larger stack closer to other PC platforms
// (1MB) and users can always inject their own link-args to override this.
cmd.arg("-z").arg("stack-size=1048576");

// By default LLD's memory layout is:
//
// 1. First, a blank page
// 2. Next, all static data
// 3. Finally, the main stack (which grows down)
//
// This has the unfortunate consequence that on stack overflows you
// corrupt static data and can cause some exceedingly weird bugs. To
// help detect this a little sooner we instead request that the stack is
// placed before static data.
//
// This means that we'll generate slightly larger binaries as references
// to static data will take more bytes in the ULEB128 encoding, but
// stack overflow will be guaranteed to trap as it underflows instead of
// corrupting static data.
cmd.arg("--stack-first");

// FIXME we probably shouldn't pass this but instead pass an explicit
// whitelist of symbols we'll allow to be undefined. Unfortunately
// though we can't handle symbols like `log10` that LLVM injects at a
// super late date without actually parsing object files. For now let's
// stick to this and hopefully fix it before stabilization happens.
cmd.arg("--allow-undefined");

// For now we just never have an entry symbol
cmd.arg("--no-entry");

// Make the default table accessible
cmd.arg("--export-table");

// Rust code should never have warnings, and warnings are often
// indicative of bugs, let's prevent them.
cmd.arg("--fatal-warnings");

// The symbol visibility story is a bit in flux right now with LLD.
// It's... not entirely clear to me what's going on, but this looks to
// make everything work when `export_symbols` isn't otherwise called for
// things like executables.
cmd.arg("--export-dynamic");

// LLD only implements C++-like demangling, which doesn't match our own
// mangling scheme. Tell LLD to not demangle anything and leave it up to
// us to demangle these symbols later.
cmd.arg("--no-demangle");

WasmLd { cmd, sess, info }
}
}

impl<'a> Linker for WasmLd<'a> {
fn link_dylib(&mut self, lib: &str) {
self.cmd.arg("-l").arg(lib);
Expand Down Expand Up @@ -982,61 +1039,6 @@ impl<'a> Linker for WasmLd<'a> {
}

fn finalize(&mut self) -> Command {
// There have been reports in the wild (rustwasm/wasm-bindgen#119) of
// using threads causing weird hangs and bugs. Disable it entirely as
// this isn't yet the bottleneck of compilation at all anyway.
self.cmd.arg("--no-threads");

// By default LLD only gives us one page of stack (64k) which is a
// little small. Default to a larger stack closer to other PC platforms
// (1MB) and users can always inject their own link-args to override this.
self.cmd.arg("-z").arg("stack-size=1048576");

// By default LLD's memory layout is:
//
// 1. First, a blank page
// 2. Next, all static data
// 3. Finally, the main stack (which grows down)
//
// This has the unfortunate consequence that on stack overflows you
// corrupt static data and can cause some exceedingly weird bugs. To
// help detect this a little sooner we instead request that the stack is
// placed before static data.
//
// This means that we'll generate slightly larger binaries as references
// to static data will take more bytes in the ULEB128 encoding, but
// stack overflow will be guaranteed to trap as it underflows instead of
// corrupting static data.
self.cmd.arg("--stack-first");

// FIXME we probably shouldn't pass this but instead pass an explicit
// whitelist of symbols we'll allow to be undefined. Unfortunately
// though we can't handle symbols like `log10` that LLVM injects at a
// super late date without actually parsing object files. For now let's
// stick to this and hopefully fix it before stabilization happens.
self.cmd.arg("--allow-undefined");

// For now we just never have an entry symbol
self.cmd.arg("--no-entry");

// Make the default table accessible
self.cmd.arg("--export-table");

// Rust code should never have warnings, and warnings are often
// indicative of bugs, let's prevent them.
self.cmd.arg("--fatal-warnings");

// The symbol visibility story is a bit in flux right now with LLD.
// It's... not entirely clear to me what's going on, but this looks to
// make everything work when `export_symbols` isn't otherwise called for
// things like executables.
self.cmd.arg("--export-dynamic");

// LLD only implements C++-like demangling, which doesn't match our own
// mangling scheme. Tell LLD to not demangle anything and leave it up to
// us to demangle these symbols later.
self.cmd.arg("--no-demangle");

::std::mem::replace(&mut self.cmd, Command::new(""))
}

Expand Down