zenith ferry
I want to embed a file into a custom section in a WASM module. The following line does not work:
export var manifest linksection("+tag doc:manifest") = @embedFile("manifest.json").*;
Variations I have tried include export const, var, removing the .*. That is the section name I need, but I have also checked that it does not work with a more 'conventional' name like .foo.
silk meadow
I'm not 100% on what "does not work" means, but try the @export builtin:
const foo = @embedFile("foo.txt");
comptime {
@export(&foo, .{ .name = "bar", .section = ".baz" });
}
then compile:
zig build-exe whatevs.zig -target wasm32-freestanding -fno-entry --export=bar
you should get .wasm that has the file exported in the named section; note that the exported symbol is named bar in this example , because it's more confusing like that
zenith ferry
By 'does not work' I mean that wasm-objdump -h shows no such section in the final artifact. And the same goes for that @export invocation.
neon harness
it seems to export the section as a symbol if you look at llvm-nm
it looks like zig needs to emit some weird wasm specific thing, https://github.com/llvm/llvm-project/commit/cfd44a2e69fa0897d944bc66ca517a7d079c135d
doesnt even work in clang
zenith ferry
Yeah, I know it's different because there shouldn't actually be a symbol per se when it works
but that's how you do it in Rust:
#[link_section = "+tag doc:manifest"]
static MANIFEST: [u8; 153] = *include_bytes!("manifest.json");
ebon palm
This is currently not supported yet. Eventually there will be a builtin for this such as @WasmCustonSection(name, value)
Linksection will put it in the data section
sleek roost
Wasm's spec isn't that complicated. Custom sections can be between any other sections in the Wasm file. Provided that the software using the custom section doesn't require a specific location (it probably doesn't), you could literally just concatenate the section to the end of the file. See the spec for what the bytes need to look like: https://webassembly.github.io/spec/core/binary/modules.html