question on gdbarch_skip_prologue()

[David Mosberger <davidm at napali dot hpl dot hp dot com>]

Hello,

I'm exploring the idea of changing the ia64 backend of gdb to use
unwind information instead of code-reading.  While looking into this,
I started to wonder how gdbarch_skip_prologue() should be implemented.
Some backends simply return the PC that was passed into the routine,
i.e., they always assume a zero-size prologue.  I'm tempted to do the
same because I worry that with optimized code, the very notion of a
prologue becomes quite fuzzy.  For example, a prologue might contain a
branch and, if so, there may not even be a single PC that corresponds
to the end of the prologue.

Are there any downsides to gdbarch_skip_prologue() always returning
the original PC?  Since the unwind info is accurate no matter what the
PC is, there are no problems with tracking the contents of preserved
(callee-saved) registers, but I'm wondering whether I'm missing
anything else.

Thanks,

	--david