Bug 248481

Summary: Alignment assumed by RegisterAtOffsetList does not accurately describe SIMD registers
Product: WebKit Reporter: David Degazio <d_degazio>
Component: WebAssemblyAssignee: David Degazio <d_degazio>
Status: RESOLVED FIXED    
Severity: Normal CC: webkit-bug-importer
Priority: P2 Keywords: InRadar
Version: WebKit Nightly Build   
Hardware: Unspecified   
OS: Unspecified   

Description David Degazio 2022-11-29 11:08:46 PST 
rdar://102515450

The current RegisterAtOffsetList implementation assumes that the alignment of a register's value is the same as the width of that register. However, 128-bit SIMD registers are currently only aligned to eight-byte intervals. This mismatch between RegisterAtOffsetList's size calculation and other locations (such as in RegisterSetBuilder) can cause assertion failure. For example:

    (module
      (type (;0;) (func (result i32 v128)))
      (func (;0;) (type 0) (result i32 v128)
        (local v128)
        i32.const 0
        v128.const i32x4 0x00000000 0x00000000 0x00000000 0x00000000
      )
      (export "foo" (func 0))
    )

...results in:

    ASSERTION FAILED: static_cast<size_t>(offset - startOffset) == sizeOfAreaInBytes
Comment 1 David Degazio 2022-11-29 11:32:01 PST 
Pull request: https://github.com/WebKit/WebKit/pull/6929
Comment 2 EWS 2022-11-30 12:53:26 PST 
Committed 257192@main (f958a5f2b00b): <https://commits.webkit.org/257192@main>

Reviewed commits have been landed. Closing PR #6929 and removing active labels.