wasm-snip
wasm-snip replaces a Wasm function's body with an unreachable instruction.
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wasm-snip replaces a WebAssembly function's body with an unreachable.
Maybe you know that some function will never be called at runtime, but the compiler can't prove that at compile time? Snip it! All the functions it transitively called — which weren't called by anything else and therefore could also never be called at runtime — will get removed too.
Very helpful when shrinking the size of WebAssembly binaries!
This functionality relies on the "name" section being present in the .wasm file, so build with debug symbols:
[profile.release]
debug = true
Executable
To install the wasm-snip executable, run
$ cargo install wasm-snip
You can use wasm-snip to remove the annoying_space_waster function from input.wasm and put the new binary in output.wasm like this:
$ wasm-snip input.wasm -o output.wasm annoying_space_waster
For information on using the wasm-snip executable, run
$ wasm-snip --help
And you'll get the most up-to-date help text, like:
Replace a wasm function with an `unreachable`.
USAGE:
wasm-snip [FLAGS] [OPTIONS] <input> [--] [function]...
FLAGS:
-h, --help Prints help information
--snip-rust-fmt-code Snip Rust's `std::fmt` and `core::fmt` code.
--snip-rust-panicking-code Snip Rust's `std::panicking` and `core::panicking` code.
-V, --version Prints version information
OPTIONS:
-o, --output <output> The path to write the output wasm file to. Defaults to stdout.
-p, --pattern <pattern>... Snip any function that matches the given regular expression.
ARGS:
<input> The input wasm file containing the function(s) to snip.
<function>... The specific function(s) to snip. These must match exactly. Use the -p flag for fuzzy matching.
Library
To use wasm-snip as a library, add this to your Cargo.toml:
[dependencies.wasm-snip]
# Do not build the executable.
default-features = false
See docs.rs/wasm-snip for API documentation.
License
Licensed under either of
at your option.
Contributing
See CONTRIBUTING.md for hacking.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.
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