wasmtime / Issue #2498 fuzzing: Use `wasm-encoder` rather... · git-wasmtime

Stream: git-wasmtime

Topic: wasmtime / Issue #2498 fuzzing: Use `wasm-encoder` rather...

Wasmtime GitHub notifications bot (Dec 11 2020 at 17:53):

In https://github.com/bytecodealliance/wasmtime/pull/2497#discussion_r541118846 we added support for generating nested modules, and we generate these modules by concatenating strings of WAT and then passing it to Module::new which internally checks for WAT strings and assembles them into Wasm bytes if necessary.

We can make this more efficient, improving the number of test cases we fuzz in a given amount of time, by generating Wasm bytes directly via the wasm-encoder crate, rather than generating a WAT string. The wasm-encoder crate has builder methods that should make it pretty straightforward to translate the WatGenerator into a WasmGenerator.

If you want to work on this issue, leave a comment, and let me know whatever questions you have!

Info for getting up and running with contributing: https://docs.wasmtime.dev/contributing.html

Wasmtime GitHub notifications bot (Dec 11 2020 at 17:53):

fitzgen labeled Issue #2498:

In https://github.com/bytecodealliance/wasmtime/pull/2497#discussion_r541118846 we added support for generating nested modules, and we generate these modules by concatenating strings of WAT and then passing it to Module::new which internally checks for WAT strings and assembles them into Wasm bytes if necessary.

We can make this more efficient, improving the number of test cases we fuzz in a given amount of time, by generating Wasm bytes directly via the wasm-encoder crate, rather than generating a WAT string. The wasm-encoder crate has builder methods that should make it pretty straightforward to translate the WatGenerator into a WasmGenerator.

If you want to work on this issue, leave a comment, and let me know whatever questions you have!

Info for getting up and running with contributing: https://docs.wasmtime.dev/contributing.html

Wasmtime GitHub notifications bot (Dec 11 2020 at 17:53):

fitzgen labeled Issue #2498:

In https://github.com/bytecodealliance/wasmtime/pull/2497#discussion_r541118846 we added support for generating nested modules, and we generate these modules by concatenating strings of WAT and then passing it to Module::new which internally checks for WAT strings and assembles them into Wasm bytes if necessary.

We can make this more efficient, improving the number of test cases we fuzz in a given amount of time, by generating Wasm bytes directly via the wasm-encoder crate, rather than generating a WAT string. The wasm-encoder crate has builder methods that should make it pretty straightforward to translate the WatGenerator into a WasmGenerator.

If you want to work on this issue, leave a comment, and let me know whatever questions you have!

Info for getting up and running with contributing: https://docs.wasmtime.dev/contributing.html

Wasmtime GitHub notifications bot (Dec 11 2020 at 17:53):

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Wasmtime GitHub notifications bot (Dec 12 2020 at 03:05):

stevenbarragan commented on Issue #2498:

Hi @fitzgen I'd love to start contributing to wasmtime. Let me dive in and try to figure it out. I'll follow in here with questions.

Wasmtime GitHub notifications bot (Dec 14 2020 at 18:08):

fitzgen commented on Issue #2498:

@stevenbarragan great! One thing to be aware of, that I forgot to mention when filing this issue, is that the WAT text format is a tiny bit higher level than Wasm is at the byte level. For example, WAT allows you to define a function and its signature type at the same time, while wasm bytes require you to pre-declare a function signature type and then reference that type via its index from the function.

That is, this WAT snippet:
(func (param i32 i32) (result i32) ...)
desugars to basically this wasm-encoder usage:
// Define a function signature in the `Type` section.
let mut types = wasm_encoder::TypeSection::new();
types.function(
    vec![wasm_encoder::ValType::I32, wasm_encoder::ValType::I32],
    vec![wasm_encoder::ValType::I32],
);

// Declare the function's type in the `Function` section.
let mut funcs = wasm_encoder::FunctionSection::new();
funcs.func(0); // first type in type section

let locals = vec![...];
let mut func = Function::new(locals);
// call `func.instruction(...)` to define instructions in this function body...

// Add the function body to the `Code` section.
let mut code = wasm_encoder::CodeSection::new();
code.function(&body);
Let me know if you aren't sure about how to translate any given snippet of WAT into wasm-encoder API calls and I can help you out.

Wasmtime GitHub notifications bot (Dec 30 2020 at 08:24):

misapprehand commented on Issue #2498:

Hi @fitzgen, I commit PR 2535 about this issue.
But I still have some questions

I cannot find the functions "dummy_instance" and "dummy_module" is called. So I just run fuzz_target compile and instantiate. But I not sure whether it is the right to check the two functions which use wat generator
Cannot find how to convert from wasm::ValType::V128 to wasm_encoder::ValType and wasm_encoder::Instruction
See file wencoder_generator.rs , commented by //TODO

In wencoder_generator.rs
fn value_to_instruction(ty: &ValType) -> Instruction {
    match ty {
       ....
        ValType::V128 => Instruction::F64Const(0.0), // TODO Do not know the right Instrunction type
        ...
    }
}
fn value_to_value(from: &ValType) -> wasm_encoder::ValType {
    match from {
        ...
        ValType::V128 => wasm_encoder::ValType::FuncRef, // TODO Do not know the right value
       ...
    }
}

3 . The u32 value 0 in Export Type is right ?
eg. Export::Function(0) ,Export::Global(0) .

fn extern_to_export(val: &wasmtime::ExternType) -> wasm_encoder::Export {
    match val {
        wasmtime::ExternType::Func(_) => wasm_encoder::Export::Function(0),   <--- 0 is right ?
        wasmtime::ExternType::Global(_) => wasm_encoder::Export::Global(0),
        wasmtime::ExternType::Table(_) => wasm_encoder::Export::Table(0),
        wasmtime::ExternType::Memory(_) => wasm_encoder::Export::Memory(0),
        wasmtime::ExternType::Instance(_) => wasm_encoder::Export::Instance(0),
        wasmtime::ExternType::Module(_) => wasm_encoder::Export::Module(0),
    }
}

Wasmtime GitHub notifications bot (Dec 30 2020 at 12:08):

misapprehand edited a comment on Issue #2498:

Hi @fitzgen, I commit PR 2535 about this issue.
But I still have some questions

Cannot find how to convert from wasm::ValType::V128 to wasm_encoder::ValType and wasm_encoder::Instruction
See file wencoder_generator.rs , commented by //TODO

In wencoder_generator.rs
fn value_to_instruction(ty: &ValType) -> Instruction {
    match ty {
       ....
        ValType::V128 => Instruction::F64Const(0.0), // TODO Do not know the right Instrunction type
        ...
    }
}
fn value_to_value(from: &ValType) -> wasm_encoder::ValType {
    match from {
        ...
        ValType::V128 => wasm_encoder::ValType::FuncRef, // TODO Do not know the right value
       ...
    }
}

2 . The u32 value 0 in Export Type is right ?
eg. Export::Function(0) ,Export::Global(0) .

fn extern_to_export(val: &wasmtime::ExternType) -> wasm_encoder::Export {
    match val {
        wasmtime::ExternType::Func(_) => wasm_encoder::Export::Function(0),   <--- 0 is right ?
        wasmtime::ExternType::Global(_) => wasm_encoder::Export::Global(0),
        wasmtime::ExternType::Table(_) => wasm_encoder::Export::Table(0),
        wasmtime::ExternType::Memory(_) => wasm_encoder::Export::Memory(0),
        wasmtime::ExternType::Instance(_) => wasm_encoder::Export::Instance(0),
        wasmtime::ExternType::Module(_) => wasm_encoder::Export::Module(0),
    }
}

Wasmtime GitHub notifications bot (Jan 05 2021 at 18:41):

fitzgen commented on Issue #2498:

Re (1) we just haven't implemented v128 support in wasm-encoder. I've opened https://github.com/bytecodealliance/wasm-tools/pull/187 to add enough support to unblock you here.

Wasmtime GitHub notifications bot (Jan 05 2021 at 18:53):

fitzgen commented on Issue #2498:

Re (2) I think we want a num_funcs member and num_globals member of the Wencoder builder struct and then export should define the given item, let its index be the current self.num_whatever value, and then increment self.num_whatever. This index is then the thing that should be used instead of 0 in wasm_encoder::Export::Whatever.

Does that make sense?

Wasmtime GitHub notifications bot (Jan 08 2021 at 10:15):

misapprehand commented on Issue #2498:

self.num_whatever just list self.tmp in WatGenerator ?

pub struct WatGenerator {
    tmp: usize,    <---   is it num_funcs?
    dst: String,
}

Wasmtime GitHub notifications bot (Jan 08 2021 at 19:13):

fitzgen commented on Issue #2498:

There needs to be a separate counter for each index space: one for globals, one for tables, one for functions, one for memories.

The tmp member was a hack for generating unique names in WAT. Unlike WAT, raw Wasm doesn't have names, so we have to refer to things by the actual index.

Wasmtime GitHub notifications bot (Jan 12 2021 at 02:14):

misapprehand commented on Issue #2498:

Make sense. I will update PR after wasm_encoder has updated. :)

Wasmtime GitHub notifications bot (Jan 12 2021 at 18:14):

fitzgen commented on Issue #2498:

after wasm_encoder has updated

Already published :)

Wasmtime GitHub notifications bot (Jan 16 2021 at 07:15):

misapprehand commented on Issue #2498:

@fitzgen, I have updated PR 2535

Wasmtime GitHub notifications bot (Feb 03 2021 at 10:33):

misapprehand commented on Issue #2498:

@fitzgen, I have updated PR 2535. There are two questions.

In function mudle_init, I am not sure the nth of type in embedded module. I use enumerate index. I think it may not correct.
Current test case only import/export simple module. Can you add more complex modules to test case?

    fn module_init<'a>(&mut self, module: &'a mut Module, item_type: &ModuleType) -> &'a Module {
        let mut import_section = ImportSection::new();

        for (i, imp) in item_type.imports().into_iter().enumerate() {
            import_section.import(
                imp.module(),
                imp.name(),
                extern_to_entity(&imp.ty(), i as u32),    <-- I use i as nth of type
            );
        }
        module.section(&import_section);

        let mut export_section = ExportSection::new();
        for (i, exp) in item_type.exports().into_iter().enumerate() {
            export_section.export(&exp.name(), extern_to_export(&exp.ty(), i as u32));     <-- I use i as nth of type
        }
        module.section(&export_section);
        module
    }

I do not find the way to instantiate which module. My current solution is instantiate one by one from Vec _self.modules_for_instantiate_ which stores all the export module index.

    fn item_import(&mut self, ty: &ExternType) {
         .....

            ExternType::Instance(v) => {
               ...
               // No sure following code is right
                if !self.modules_for_instantiate.is_empty() {
                    self.instance_section.instantiate(
                        self.modules_for_instantiate.remove(0),
                        v.exports()
                            .into_iter()
                            .enumerate()
                            .map(|(i, it)| (it.name(), extern_to_export(&it.ty(), i as u32))),
                    );
                    self.num_instances += 1;
                }
                self.num_instances - 1
            }

Last updated: Dec 23 2024 at 12:05 UTC