Allow unwind support to work without a frame pointer #2838
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The patch extends the unwinder to support targets that do not need to use a dedicated frame pointer register. Specifically, the changes include: - Change the "fp" routine in the RegisterMapper to return an *optional* frame pointer regsiter via Option<Register>. - On targets that choose to not define a FP register via the above routine, the UnwindInst::DefineNewFrame operation no longer switches the CFA to be defined in terms of the FP. (The operation still can be used to define the location of the clobber area.) - In addition, on targets that choose not to define a FP register, the UnwindInst::PushFrameRegs operation is not supported. - There is a new operation UnwindInst::StackAlloc that needs to be called on targets without FP whenever the stack pointer is updated. This caused the CFA offset to be adjusted accordingly. (On targets with FP this operation is a no-op.)
cfallin
approved these changes
Apr 14, 2021
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The patch extends the unwinder to support targets that do not need
to use a dedicated frame pointer register. Specifically, the
changes include:
Change the "fp" routine in the RegisterMapper to return an
optional frame pointer regsiter via Option.
On targets that choose to not define a FP register via the above
routine, the UnwindInst::DefineNewFrame operation no longer switches
the CFA to be defined in terms of the FP. (The operation still can
be used to define the location of the clobber area.)
In addition, on targets that choose not to define a FP register, the
UnwindInst::PushFrameRegs operation is not supported.
There is a new operation UnwindInst::StackAlloc that needs to be
called on targets without FP whenever the stack pointer is updated.
This caused the CFA offset to be adjusted accordingly. (On
targets with FP this operation is a no-op.)