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Why do we have two ways of finding sniffers?
- From: Jim Blandy <jimb at redhat dot com>
- To: gdb at sourceware dot org
- Date: Wed, 19 Oct 2005 17:16:46 -0700
- Subject: Why do we have two ways of finding sniffers?
Looking at frame-unwind.c and frame-unwind.h, it seems like there are
two mostly equivalent ways to register frame unwinding methods. Why
do we have two ways, instead of just one? The comments in
frame-unwind.h don't really explain why it's helpful.
The only function that scans the list of unwinders is
frame_unwind_by_frame: it takes a NEXT frame, and returns a 'struct
frame_unwind *' if it can find one.
It works by walking the NEXT frame's gdbarch's list of frame
unwinders. Each entry in the list is one of two possible kinds:
- If the entry points to a frame_unwind_sniffer_ftype function, that
takes the next frame's frame_info; if it likes it, then it returns a
'struct frame_unwind *' to use for this frame.
- If the entry points to a 'struct frame_unwind' object, that contains
its own sniffer, which takes a pointer to the 'struct frame_unwind',
the next frame's frame_info, and a prologue cache, and just returns
a boolean indicating whether this is an appropriate frame_unwind for
it.
I don't understand why we need both alternatives. Shouldn't it be
sufficient to simply have each entry in the list point to a function
that expects the next frame's frame_info and a prologue cache, and
returns a 'struct frame_unwind *' or zero?