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https://github.com/fluencelabs/wasm-bindgen
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b256b98e38
Previously the `link_mem_intrinsics` hack actually had a runtime overhead by storing a value into a global location, but it turns out we can actually use a non-inlined function call as part of the *descriptor* which requires this to be in the final binary, but we'll end up snip'ing the value at the end. All in all this should mean that it's not a zero-overhead solution for linking these intrinsics! The `#[wasm_bindgen]` attribute already has other problems if the descriptors don't show up, so that's the least of our issues!
67 lines
1.7 KiB
Markdown
67 lines
1.7 KiB
Markdown
# Small wasm files
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[View full source code][code] or [view the compiled example online][online]
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[online]: https://rustwasm.github.io/wasm-bindgen/exbuild/add/
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[code]: https://github.com/rustwasm/wasm-bindgen/tree/master/examples/add
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One of `wasm-bindgen`'s core goals is a pay-only-for-what-you-use philosophy, so
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if we don't use much then we shouldn't be paying much! As a result
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`#[wasm_bindgen]` can generate super-small executables
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Currently this code...
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```rust
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{{#include ../../../examples/add/src/lib.rs}}
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```
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generates a 710 byte wasm binary:
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```
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$ ls -l add_bg.wasm
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-rw-rw-r-- 1 alex alex 710 Sep 19 17:32 add_bg.wasm
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```
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If you run [wasm-opt], a C++ tool for optimize WebAssembly, you can make it
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even smaller too!
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```
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$ wasm-opt -Os add_bg.wasm -o add.wasm
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$ ls -l add.wasm
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-rw-rw-r-- 1 alex alex 172 Sep 19 17:33 add.wasm
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```
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And sure enough, using the [wasm2wat] tool it's quite small!
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```
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$ wasm2wat add.wasm
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(module
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(type (;0;) (func (param i32 i32) (result i32)))
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(func (;0;) (type 0) (param i32 i32) (result i32)
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get_local 1
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get_local 0
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i32.add)
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(table (;0;) 1 1 anyfunc)
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(memory (;0;) 17)
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(global (;0;) i32 (i32.const 1049118))
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(global (;1;) i32 (i32.const 1049118))
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(export "memory" (memory 0))
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(export "__indirect_function_table" (table 0))
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(export "__heap_base" (global 0))
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(export "__data_end" (global 1))
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(export "add" (func 0))
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(data (i32.const 1049096) "invalid malloc request"))
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```
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Also don't forget to compile in release mode for the smallest binaries! For
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larger applications you'll likely also want to turn on LTO to generate the
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smallest binaries:
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```toml
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[profile.release]
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lto = true
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```
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[wasm2wat]: https://github.com/webassembly/wabt
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[wasm-opt]: https://github.com/webassembly/binaryen
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