Re: [just for the record]: new prologue analyzer for S/390

[Andrew Cagney <ac131313 at redhat dot com>]

> I think this patch shouldn't be committed; I'm just posting it for
> reference.
>
> This patch implements a new prologue analyzer for the S/390.  It's
> meant to be general enough to handle the complex prologues GCC emits
> on the S/390, and robust enough to tolerate compiler changes.  In my
> experience, it does pretty well, even on optimized code.
>
> However, the S/390 GDB folks at IBM and I agree that GDB on the S/390
> should move towards using Dwarf 2 CFI and location lists whenever
> possible, and do only minimal prologue analysis to handle those few
> common cases where Dwarf 2 CFI is not available.  And it looks to me
> as if the work needed in GDB's core code to make it possible for any
> target to use Dwarf 2 CFI is almost complete.  In that light, it
> doesn't make sense to dump a new, large, complex prologue analyzer
> into the code base that will soon be eclipsed by a better solution.

It is important to ensure that all technical decisions related to GDB 
are discussed here, in this forum.  Issues, specific to this change, 
that come to mind, include:

- the unpredictability of the CFI timetable (a bird in the hand vs ...)

- the unpredictability of the legal processes sometimes required before 
accepting changes (must assume that the change doesn't exist)

- the need to get the existing s390's frame code updated so that it 
implements frame-unwind (this is in addition, and largely orthogonal to 
the missing generic CFI unwinder).  Ignoring s390_get_signal_frame_info, 
which should be separated out, the attached appears to only affect the 
prologe analyzer so is relatively independant?

- the need to have gdb behave reasonably well when there is no, or 
minimal, debug info

- the need to fix the s390 problem of having a wrong frame ID . 
stack_addr (does this change address that problem?)

- what tests it actually fixes (data?)

> This patch assumes that IBM's s390x ABI patch has been applied.  That
> patch is currently working its way through the IBM/FSF IP process.
> http://sources.redhat.com/ml/gdb-patches/2003-02/msg00097.html

To be honest, I don't understand the dependency.  This patch modifies 
the prologue analysier while the other change appears to be fixing the 
push_arguments function.  While they might interact in positive ways, I 
don't think that they are dependant.

I'd also strongly recommend putting your the file / changes through 
gdb_indent.sh - GNU indent will likely have a field day on the 
formatting of the comments :-(

Andrew