Stream: git-wasmtime

Topic: wasmtime / Issue #1435 #[repr(align(...))] structures cau...

view this post on Zulip Wasmtime GitHub notifications bot (Mar 30 2020 at 18:26):

marmistrz labeled Issue #1435:

I'm not sure if I should report this issue here or in rust-lang/rust or even somewhere else.

Consider the following code:

#[repr(align(64))]
#[derive(Copy, Clone, Default, Debug)]
pub struct CacheBucket([CacheEntry; 3]);

#[repr(C)]
#[derive(Copy, Clone, Default, Debug)]
pub struct CacheEntry {
    pub alpha: bool
}

fn main() {
    let buckets = 4194304;
    let xd = vec![CacheBucket::default(); buckets];
    println!("{:?}", xd);
}

compiled to wasm using rustup run stable cargo build --target=wasm32-wasi with rustc 1.42.0 (b8cedc004 2020-03-09)

Then run the wasm binary using wasmtime:

$ cargo run --release -- run oob.wasm
    Finished release [optimized] target(s) in 0.09s
     Running `target/release/wasmtime run ../chess/oob/target/wasm32-wasi/debug/oob.wasm`
Error: failed to run main module `../chess/oob/target/wasm32-wasi/debug/oob.wasm`

Caused by:
    0: failed to invoke `_start`
    1: wasm trap: out of bounds memory access, source location: @56bf
       wasm backtrace:
         0: <unknown>!core::ptr::write::h5550856a4b897d6d
         1: <unknown>!alloc::vec::Vec<T>::extend_with::h42807d753bccf81d
         2: <unknown>!<T as alloc::vec::SpecFromElem>::from_elem::h3a932571fd38db0f
         3: <unknown>!alloc::vec::from_elem::ha55e830b1b839b10
         4: <unknown>!oob::main::h5b4df0d7d93a566d
         5: <unknown>!std::rt::lang_start::{{closure}}::h4b37f8cbafc64616
         6: <unknown>!std::sys_common::backtrace::__rust_begin_short_backtrace::h09ce0967d7b1e05d
         7: <unknown>!std::panicking::try::do_call::h9f56360d08e2b60c
         8: <unknown>!__rust_maybe_catch_panic
         9: <unknown>!std::rt::lang_start_internal::h1c0f367ef14e29b3
         10: <unknown>!std::rt::lang_start::h81110b05d9ba24fa
         11: <unknown>!__original_main
         12: <unknown>!_start

The code runs correctly if buckets is small (e.g. 4) or if #[repr(align(64))] is removed.
wasmtime master, 78772cf5e1d019d060d2a5427aa7058604f924e5

view this post on Zulip Wasmtime GitHub notifications bot (Mar 30 2020 at 18:26):

marmistrz opened Issue #1435:

I'm not sure if I should report this issue here or in rust-lang/rust or even somewhere else.

Consider the following code:

#[repr(align(64))]
#[derive(Copy, Clone, Default, Debug)]
pub struct CacheBucket([CacheEntry; 3]);

#[repr(C)]
#[derive(Copy, Clone, Default, Debug)]
pub struct CacheEntry {
    pub alpha: bool
}

fn main() {
    let buckets = 4194304;
    let xd = vec![CacheBucket::default(); buckets];
    println!("{:?}", xd);
}

compiled to wasm using rustup run stable cargo build --target=wasm32-wasi with rustc 1.42.0 (b8cedc004 2020-03-09)

Then run the wasm binary using wasmtime:

$ cargo run --release -- run oob.wasm
    Finished release [optimized] target(s) in 0.09s
     Running `target/release/wasmtime run ../chess/oob/target/wasm32-wasi/debug/oob.wasm`
Error: failed to run main module `../chess/oob/target/wasm32-wasi/debug/oob.wasm`

Caused by:
    0: failed to invoke `_start`
    1: wasm trap: out of bounds memory access, source location: @56bf
       wasm backtrace:
         0: <unknown>!core::ptr::write::h5550856a4b897d6d
         1: <unknown>!alloc::vec::Vec<T>::extend_with::h42807d753bccf81d
         2: <unknown>!<T as alloc::vec::SpecFromElem>::from_elem::h3a932571fd38db0f
         3: <unknown>!alloc::vec::from_elem::ha55e830b1b839b10
         4: <unknown>!oob::main::h5b4df0d7d93a566d
         5: <unknown>!std::rt::lang_start::{{closure}}::h4b37f8cbafc64616
         6: <unknown>!std::sys_common::backtrace::__rust_begin_short_backtrace::h09ce0967d7b1e05d
         7: <unknown>!std::panicking::try::do_call::h9f56360d08e2b60c
         8: <unknown>!__rust_maybe_catch_panic
         9: <unknown>!std::rt::lang_start_internal::h1c0f367ef14e29b3
         10: <unknown>!std::rt::lang_start::h81110b05d9ba24fa
         11: <unknown>!__original_main
         12: <unknown>!_start

The code runs correctly if buckets is small (e.g. 4) or if #[repr(align(64))] is removed.
wasmtime master, 78772cf5e1d019d060d2a5427aa7058604f924e5

view this post on Zulip Wasmtime GitHub notifications bot (Mar 30 2020 at 19:12):

bjorn3 commented on Issue #1435:

How much memory is the wasm module allowed to use? The version with #[repr(align(64))] would need 256MiB for buckets alone, while the version without would need just 16MiB.

view this post on Zulip Wasmtime GitHub notifications bot (Mar 30 2020 at 19:17):

marmistrz commented on Issue #1435:

How should I check it? For reference, the original structure looks like this:

pub struct CacheEntry {
    pub alpha: bool,
    pub beta: bool,
    pub pv_node: bool,
    pub depth: i8,
    pub plies_played: u16,
    pub score: i16,
    pub upper_hash: u32,
    pub lower_hash: u32,
    pub mv: u16,
    pub static_evaluation: i16,
}

Switching to this defintion of CacheEntry doesn't change anything.

view this post on Zulip Wasmtime GitHub notifications bot (Mar 30 2020 at 19:20):

pchickey commented on Issue #1435:

FWIW: Lucet gets a HeapOutOfBounds fault running this module (as I compiled it locally with 1.40, we're still stuck on snapshot 0).

view this post on Zulip Wasmtime GitHub notifications bot (Mar 30 2020 at 19:34):

alexcrichton commented on Issue #1435:

Looks like this was a bug in the Rust standard library, fixed here.

As a local workaround while we wait for that to propagate you can depend directly on dlmalloc and use that as a global allocator:

# in Cargo.toml
[dependencies]
dlmalloc = { version ="0.1", features = ['global'] }

#[global_allocator]
static A: dlmalloc::GlobalDlmalloc = dlmalloc::GlobalDlmalloc;

#[repr(align(64))]
#[derive(Copy, Clone, Default, Debug)]
pub struct CacheBucket([CacheEntry; 3]);

#[repr(C)]
#[derive(Copy, Clone, Default, Debug)]
pub struct CacheEntry {
    pub alpha: bool,
}

fn main() {
    let buckets = 4194304;
    let xd = vec![CacheBucket::default(); buckets];
    let string = format!("{:?}", xd);
    println!("{}", string.len());
}

view this post on Zulip Wasmtime GitHub notifications bot (Mar 30 2020 at 19:35):

alexcrichton edited a comment on Issue #1435:

Looks like this was a bug in the Rust standard library, fixed here.

As a local workaround while we wait for that to propagate you can depend directly on dlmalloc and use that as a global allocator:

# in Cargo.toml
[dependencies]
dlmalloc = { version = "0.1", features = ['global'] }

#[global_allocator]
static A: dlmalloc::GlobalDlmalloc = dlmalloc::GlobalDlmalloc;

#[repr(align(64))]
#[derive(Copy, Clone, Default, Debug)]
pub struct CacheBucket([CacheEntry; 3]);

#[repr(C)]
#[derive(Copy, Clone, Default, Debug)]
pub struct CacheEntry {
    pub alpha: bool,
}

fn main() {
    let buckets = 4194304;
    let xd = vec![CacheBucket::default(); buckets];
    let string = format!("{:?}", xd);
    println!("{}", string.len());
}

view this post on Zulip Wasmtime GitHub notifications bot (Apr 27 2020 at 11:03):

marmistrz commented on Issue #1435:

This works for me on nightly, so I guess we can close it.

view this post on Zulip Wasmtime GitHub notifications bot (Apr 27 2020 at 14:52):

alexcrichton closed Issue #1435:

I'm not sure if I should report this issue here or in rust-lang/rust or even somewhere else.

Consider the following code:

#[repr(align(64))]
#[derive(Copy, Clone, Default, Debug)]
pub struct CacheBucket([CacheEntry; 3]);

#[repr(C)]
#[derive(Copy, Clone, Default, Debug)]
pub struct CacheEntry {
    pub alpha: bool
}

fn main() {
    let buckets = 4194304;
    let xd = vec![CacheBucket::default(); buckets];
    println!("{:?}", xd);
}

compiled to wasm using rustup run stable cargo build --target=wasm32-wasi with rustc 1.42.0 (b8cedc004 2020-03-09)

Then run the wasm binary using wasmtime:

$ cargo run --release -- run oob.wasm
    Finished release [optimized] target(s) in 0.09s
     Running `target/release/wasmtime run ../chess/oob/target/wasm32-wasi/debug/oob.wasm`
Error: failed to run main module `../chess/oob/target/wasm32-wasi/debug/oob.wasm`

Caused by:
    0: failed to invoke `_start`
    1: wasm trap: out of bounds memory access, source location: @56bf
       wasm backtrace:
         0: <unknown>!core::ptr::write::h5550856a4b897d6d
         1: <unknown>!alloc::vec::Vec<T>::extend_with::h42807d753bccf81d
         2: <unknown>!<T as alloc::vec::SpecFromElem>::from_elem::h3a932571fd38db0f
         3: <unknown>!alloc::vec::from_elem::ha55e830b1b839b10
         4: <unknown>!oob::main::h5b4df0d7d93a566d
         5: <unknown>!std::rt::lang_start::{{closure}}::h4b37f8cbafc64616
         6: <unknown>!std::sys_common::backtrace::__rust_begin_short_backtrace::h09ce0967d7b1e05d
         7: <unknown>!std::panicking::try::do_call::h9f56360d08e2b60c
         8: <unknown>!__rust_maybe_catch_panic
         9: <unknown>!std::rt::lang_start_internal::h1c0f367ef14e29b3
         10: <unknown>!std::rt::lang_start::h81110b05d9ba24fa
         11: <unknown>!__original_main
         12: <unknown>!_start

The code runs correctly if buckets is small (e.g. 4) or if #[repr(align(64))] is removed.
wasmtime master, 78772cf5e1d019d060d2a5427aa7058604f924e5

Last updated: Dec 23 2024 at 12:05 UTC