Re: [rfa/mips] Stop backtraces when we've lost the PC

[Andrew Cagney <cagney@gnu.org>]

> On Thu, Mar 11, 2004 at 03:51:11PM -0500, Andrew Cagney wrote:
> 
>>>> >I hypothesize that if two consecutive frames, regardless of their type,
>>>> >claim to save the PC register at the same location, then unwinding is
>>>> >hosed.
>>
>>> 
>>> It would need to do a deep analysis of the location (think about a 
>>> register window architecture), hence I don't know that there's that much 
>>> cost benefit.

 >>> Something simpler such as a list of functions known to
>>> terminate the stack might be more useful.
> 
> 
> Er, no.  frame_unwind_register tells us where, relative to the current
> machine state, the register is saved.  If it returns lval_register and
> real_regnum == O7_REGNUM, then that means it leaves in
> read_register(O7_REGNUM) at this moment, not that it did at some point
> in the past.  Isn't that the point of the recursive unwinder?

"Er, no". to which part?  I'll assume the first half of the first half.

I suspect you're violently agreeing with me here - you're describing 
what I ment by a deep analysis of the location - tracking things all the 
way back to where in the inferior the value is.   The architecture 
vector will need to be changed, the existing function deprecated, and 
new methods implemented.  The introduction of "struct location" (or 
whatever) would then see it changed again. Given it is all for a 
marginal edge case (and to cover up breakage in glibc), I don't see any 
cost benefit in doing this.

I think a more useful mechanism is for there to be a table of "start" 
functions that the user could manipulate (but would default to values 
specified by the OSABI).

Andrew