Bugzilla

Short description of approach:
1. The wasmCollapseFrame is introduced at masm level: the operation will remove caller/middle frame by moving parameters, instance slots. RA and FP will be used to transfer control to the callee via direct jump.
2. The return call caller will prepare parameters on the stack, which will still include its own private frame + its parameters, and then proceed with wasmCollapseFrame. This will also guarantee no data will be written before current SP.
3. Every wasm callsite with slow path will be mark with special carefully selected instruction. During collapse frame, when heap registers and realm is changing, this mark is checked.
4. In case when the caller of the caller (C0) has a fast path (no heap registers and realm will be recovered), new small frame will be inserted before transferring control to the C0 for the short trampoline that will restore heap registers and realm.
5. The stack depth will be changing, so for Ion calls it will be required to restore SP based on its FP.
6. Some consideration has to be taken for the entry stubs (from interpreter or JIT) as well, the SP can be changed, so the entry stub shall anticipate that.

Short description of the current approach:
1. The wasmCollapseFrame is introduced at masm level: the operation will remove caller/middle frame by moving parameters, instance slots. RA and FP will be used to transfer control to the callee via direct jump.
2. The return call caller will prepare parameters on the stack, which will still include its own private frame + its parameters, and then proceed with wasmCollapseFrame. This will also guarantee no data will be written before current SP.
3. Every wasm callsite with slow path will be mark with special carefully selected instruction. During collapse frame, when heap registers and realm is changing, this mark is checked.
4. In case when the caller of the caller (C0) has a fast path (no heap registers and realm will be recovered), new small frame will be inserted before transferring control to the C0 for the short trampoline that will restore heap registers and realm.
5. The stack depth will be changing, so for Ion calls it will be required to restore SP based on its FP.
6. Some consideration has to be taken for the entry stubs (from interpreter or JIT) as well, the SP can be changed, so the entry stub shall anticipate that.