Stream: git-wasmtime

Topic: wasmtime / PR #5471 wiggle: copy guest slices back to sha...

Wasmtime GitHub notifications bot (Dec 19 2022 at 19:47):

abrown opened PR #5471 from wiggle-copied-reads to main:

This change upgrades UnsafeGuestSlice in Wiggle to expose more functionality to be able to use std::ptr::copy for writing bytes into Wasm shared memory. Additionally, it adds a new GuestCow type for delineating between Wasm memory regions that can be borrowed (non-shared memory) or must be copied (shared memory) in order to maintain Rust guarantees.

With these in place, it is now possible to implement the preview1 "read" functions for shared memory. Previously, these would panic if attempting to copy to a shared memory. This change removes the panic and introduces some (rather complex) logic for handling both the shared and non-shared cases:

• if reading into a Wasm non-shared memory, Wiggle guarantees that no other guest pointers will touch the memory region and, in the absence of concurrency, preview1 can write directly to this memory
• if reading into a Wasm shared memory, the memory region can be concurrently modified. At @alexcrichton's request re: Rust safety, this change copies all of the bytes into an intermediate buffer before using std::ptr::copy to move them into Wasm memory.

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Wasmtime GitHub notifications bot (Dec 19 2022 at 22:03):

abrown has marked PR #5471 as ready for review.

Wasmtime GitHub notifications bot (Dec 19 2022 at 22:32):

abrown requested alexcrichton for a review on PR #5471.

Wasmtime GitHub notifications bot (Dec 19 2022 at 23:36):

abrown updated PR #5471 from wiggle-copied-reads to main.

Wasmtime GitHub notifications bot (Dec 20 2022 at 20:00):

abrown updated PR #5471 from wiggle-copied-reads to main.

Wasmtime GitHub notifications bot (Dec 20 2022 at 20:01):

abrown edited PR #5471 from wiggle-copied-reads to main:

This change upgrades UnsafeGuestSlice in Wiggle to expose more
functionality to be able to use std::ptr::copy for writing bytes into
Wasm shared memory. Additionally, it adds a new GuestCow type for
delineating between Wasm memory regions that can be borrowed (non-shared
memory) or must be copied (shared memory) in order to maintain Rust
guarantees.

With these in place, it is now possible to implement the preview1
"read" functions for shared memory. Previously, these would panic if
attempting to copy to a shared memory. This change removes the panic and
introduces some (rather complex) logic for handling both the shared and
non-shared cases:

• if reading into a Wasm non-shared memory, Wiggle guarantees that no
  other guest pointers will touch the memory region and, in the absence
  of concurrency, a WASI function can write directly to this memory

• if reading into a Wasm shared memory, the memory region can be
  concurrently modified. At @alexcrichton's request re: Rust safety,
  this change copies all of the bytes into an intermediate buffer before
  using std::ptr::copy to move them into Wasm memory.

This change only applies to the preview0 and preview1
implementations of wasi-common. Fixing up other WASI implementations
(esp. wasi-crypto) is left for later.

Wasmtime GitHub notifications bot (Jan 03 2023 at 16:09):

alexcrichton created PR review comment:

Since random_get fills the entire buffer I think this will need to loop or otherwise this will return an error since tmp may be shorter than buf

Wasmtime GitHub notifications bot (Jan 03 2023 at 16:09):

alexcrichton submitted PR review.

Wasmtime GitHub notifications bot (Jan 03 2023 at 16:09):

alexcrichton created PR review comment:

Could you leave some comments that this is for the UnsafeCell inside?

Wasmtime GitHub notifications bot (Jan 03 2023 at 16:09):

alexcrichton submitted PR review.

Wasmtime GitHub notifications bot (Jan 03 2023 at 16:09):

alexcrichton created PR review comment:

This vec! I think can get removed (just use a [..] on the stack)

Wasmtime GitHub notifications bot (Jan 03 2023 at 18:33):

abrown updated PR #5471 from wiggle-copied-reads to main.

Wasmtime GitHub notifications bot (Jan 03 2023 at 18:33):

abrown submitted PR review.

Wasmtime GitHub notifications bot (Jan 03 2023 at 18:33):

abrown created PR review comment:

You might want to take a look at 652988f since I changed the GuestPtr API slightly.

Wasmtime GitHub notifications bot (Jan 03 2023 at 18:40):

alexcrichton submitted PR review.

Wasmtime GitHub notifications bot (Jan 03 2023 at 18:51):

abrown has enabled auto merge for PR #5471.

Wasmtime GitHub notifications bot (Jan 03 2023 at 19:51):

abrown merged PR #5471.

Last updated: Nov 22 2024 at 16:03 UTC