The bug here is very subtle, as is the mitigation.
Quick background on WASM memory, there is an object
called wasmMemory (which might be hoisted into scope for
CanvasKit's pre-js functions), of type WebAssembly.Memory
which is a resizable ArrayBuffer. Emscripten provides the
JS code to initialize this and handle size increases.
Emscripten also provides TypedArray "views" into this buffer.
These are called CanvasKit.HEAPU8, CanvasKit.HEAPF32, etc.
When there is a call to CanvasKit._malloc, wasmMemory may
be resized. If that happens, the previous TypedArray views
become invalid. However, in the same call to _malloc,
emscripten will refresh the views [1]. So, dealing with
CanvasKit.HEAPU8 directly (quick aside, we never expect clients
to mess with these views, only us in our glue JS code
[e.g. interface.js]), should always be safe because if they
were to be invalidated in a call to _malloc, the views would
be refreshed before _malloc continues.
The problem that existed before was when we were passing
CanvasKit.HEAP* as a parameter to a function, in which the
function would call _malloc before using the typed array
parameter:
//... let us suppose wasmMemory is backed by ArrayBuffer D
copy1dArray(arr, HEAPU32);
// The HEAPU32 TypedArray (backed by ArrayBuffer D) is stored
// to a function parameter "dest"
function copy1dArray(arr, dest, ptr) {
// ...
if (!ptr) {
ptr = CanvasKit._malloc(arr.length * dest.BYTES_PER_ELEMENT);
// Suppose _malloc needs to resize wasmMemory and is
// now backed by ArrayBuffer E.
// Note: The field CanvasKit.HEAPU32 is correctly backed
// by ArrayBuffer E, but variable dest still points to a
// TypedArray backed by ArrayBuffer D.
}
// dest.set will fail with a "neutered ArrayBuffer" error
// because ArrayBuffer D is effectively gone (replaced by E).
dest.set(arr, ptr / dest.BYTES_PER_ELEMENT);
The fix here is to pass in the field name indicating the TypedArray
view we want to write our data into instead of using the
view itself as the parameter.
[1] e427159553/src/preamble.js (L344)
Change-Id: I46cfb98f8bdf928b61690a5ced034a5961356398
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/294516
Reviewed-by: Nathaniel Nifong <nifong@google.com>
Uniforms in the general case can be multiple floats, so
we expose a small struct to provide information about all
uniforms (including the built in ones like "dt") as well
as effectUniforms and particleUniforms which return Float32Arrays
bound to the WASM memory containing those unifroms.
Thus, by modifying the Float32Array, one can directly affect
the particle/effect properties.
This allows us to expose sliders on particles.skia.org
(https://skia-review.googlesource.com/c/buildbot/+/272398)
Change-Id: Ie390f3d2dc571ee4ebaab59a7fa1b7b2dc24d871
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/272377
Reviewed-by: Brian Osman <brianosman@google.com>
Currently just for image drawable, but going to use this for
references to other kinds of data in bindings, too.
Change-Id: Ic6673530013337bbaadd2d3f1c040626ec24ffb8
Bug: skia:9513
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/256776
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
