[SH][PATCH] Disable ABI frame sniffer
Daniel Jacobowitz
drow@false.org
Fri Nov 11 10:35:00 GMT 2005
On Thu, Nov 10, 2005 at 02:33:01PM +0000, Andrew STUBBS wrote:
> Hmm, confusing. Well, I can change the name easily enough. It is the
> unwinder based on the ABI though. How come the unwind function is called
> sniffer?
It's not. That doesn't _do_ the unwinding, it _selects_ which unwinder
to use. Sniffs around for the right one, I suppose.
> >Quite on the contrary, my experience is that in most programs you'll
> >need it at least a couple of times, e.g. to get out of bits of libc or
> >linker-generated code.
>
> Bare-machine (or OS21) sh-elf doesn't use glibc with all its
> complications. We use newlib and we always compile it with debug info
> and CFI so there is it should never need to fall back.
There are assembly routines in newlib too, you know. I didn't say
anything about glibc. You may encounter linker generated branch
trampolines in some cases, too.
> >>It may be possible to improve the unwinder. However, it is dependent on
> >>the values in registers and in memory. It would be impossible to prevent
> >>it getting occasionally confused.
> >
> >
> >Just like the rest of GDB on both counts.
In case you missed my sarcasm here, I was responding to "dependent on
the values in registers and memory". Of course it is!
> The problem only occurs in threads (unless 'set backtrace pastmain' is
> set, in which case it happens in any program) when the backtrace falls
> off the end of the program. There are no more frames because there's no
> more stack, but there's no way to know that unless you assume the CFI
> and program run out at the same time.
See Mark's reply for more on this. Had you said what your problem
really was, we could have saved a couple of back-and-forth exchanges;
I'm extremely familiar with the problem of finding clean ways to
terminate the backtrace.
> BTW, were you (and others) waiting for them to do something about the SH
> specific patches I have been sending? I ask because I have had no
> response on a few.
I review patches as fast as I am able. I am more likely to review
patches to code I know something about, which does not include the SH
backend.
--
Daniel Jacobowitz
CodeSourcery, LLC
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