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Chris Tate
d5ac31f812
scr_unwind_raise walks the stack with plans cached per return address. The first raise through a return address finds the function's FDE through the .eh_frame_hdr of the object that contains it, runs the CFI up to the call, and finds the call site's landing pad in the LSDA; the plan records the frame's CFA rule, where its callee-saved registers are saved, and the landing pad. Later raises look the plans up, restore the registers, and jump to the first landing pad. Plans are inserted under a lock and read without one. Landing pads continue the unwind with scr_unwind_resume instead of `resume`, so the walk goes on from their frame. A frame whose CFI, pointer encodings or personality the plans do not express, or a return address without an FDE, leaves the unwind to libgcc's forced unwind from the frame the walk started at, as before. Other Linux targets keep libgcc's unwinder; their scr_unwind_resume calls _Unwind_Resume. bench:runtime gains layered-errors, a workload whose errors are thrown below small functions that hold references and caught per entry in a loop, and the corpus gains unwind-landing-pad-chains, which pins landing pads that continue the unwind, including in frames LLVM inlines into a caller whose handler takes the exception.