[40.0] Backport Cranelift: x64: fix incorrect load-sinking in copysign operator.
#12437
+109
−30
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The implementation of the `fcopysign` operator uses vector bitwise AND instructions on the floating-point/vector registers containing the inputs to the operator. This is a reasonable implementation as the instruction set does not have scalar (single-lane) bitwise operators. However, when load-sinking automatically kicks in for an operand to an `andps`, it can turn a 64-bit load (`f64.load`) into a 128-bit load incorrectly. This load-widening can cause out-of-bounds accesses where they were not expected. When dynamic bounds checks are enabled, we compile assuming the correct load-operator width is codegen'd; a too-wide load could read beyond the checked bound, either into unmapped memory (crashing the process) or, worse, valid data outside the sandbox. In the case of `fcopysign` the result of that read is not directly available, because it will go into the high (unused) lane, but the out-of-bounds read itself is a problem. Thanks to louismerlin for reporting!
fitzgen
approved these changes
Jan 26, 2026
cfallin
merged commit 728fa07
into
bytecodealliance:release-40.0.0
565 of 688 checks passed
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