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Re: [RFA] Rewrite mips_get_saved_register()
- From: Kevin Buettner <kevinb at redhat dot com>
- To: Andrew Cagney <ac131313 at ges dot redhat dot com>, Kevin Buettner <kevinb at redhat dot com>
- Cc: gdb-patches at sources dot redhat dot com
- Date: Fri, 9 Aug 2002 13:59:26 -0700
- Subject: Re: [RFA] Rewrite mips_get_saved_register()
- References: <1020809003710.ZM26327@localhost.localdomain> <3D53EA0A.2030405@ges.redhat.com>
On Aug 9, 12:12pm, Andrew Cagney wrote:
> > This patch depends on the following (as of yet) unapproved patches:
> >
> > http://sources.redhat.com/ml/gdb-patches/2002-08/msg00189.html
> > http://sources.redhat.com/ml/gdb-patches/2002-08/msg00195.html
> > http://sources.redhat.com/ml/gdb-patches/2002-08/msg00196.html
> >
> > Okay to commit?
> >
> > * mips-tdep.c (mips_get_saved_register): Rewrite to use
> > frame_register_unwind() instead of find_saved_register().
>
> Sorry, not like this. Can you please, for the moment, just in-line the
> call to find_saved_register().
>
> (The two other bugs you fixed were definitly needed and thanks for
> finding them. How the code got away with not setting the SP I don't know.)
>
> - if (raw_buffer != NULL)
> -
> {
> -
> LONGEST val;
> -
> if (regnum < 32)
> -
> /* Only MIPS_SAVED_REGSIZE bytes of GP registers are
> - saved. */
> -
> val = read_memory_integer (addr, MIPS_SAVED_REGSIZE);
> -
> else
> -
> val = read_memory_integer (addr, REGISTER_RAW_SIZE (regnum));
> -
> store_address (raw_buffer, REGISTER_RAW_SIZE (regnum), val);
> -
> }
>
> In theory (and emphasis on the theory) things need to be changed so that:
>
> - 32 32 bit nameless pseudo-registers are added to the cooked register space
> - the 32 64 bit gprs get given a 64 bit virtual type so that they have
> identical raw and virtual sizes
> - The debug info, for a 32 bit ABI, maps the gpr register numbers onto
> the 32 bit pseudo register range
> - The gdbarch pseudo register read/write function maps the 32 bit
> pseudo-registers onto the 64 bit gprs.
> - For init saved regs, dependant on the size of the register saved,
> either the the address of the 64 bit GPR or the address of the 32 bit
> pseudo-register is set
> - a custom mips register unwind function maps the requested register (64
> bit gpr or 32 bit pseudo) onto: the 32 bit pseudo, the 64 bit gpr, or a
> further recursive unwind call. If it has to do a 32/64 mapping then it
> sets not-an-lval.
> - you find you have to yank all sorts of register converible code
>
> But like I said, it is theory, the mips suffers from one hack (like the
> above) piled on top of another (the register convertable stuff, the
> register raw/virtual size being different, ...). I don't know if now is
> the time to be experimenting with theories :-)
Yes, fixing all of the above is quite a lot more work than I have time
for at the moment.
But, assuming that my rewrite is functionally equivalent to the
original, what is the reason for preferring to inline
find_saved_register() over using the new interface?
I should think that using frame_register_unwind() would:
- allow it to be better tested. E.g, I wouldn't have found
the bugs that I did recently had I not gone through this
exercise.
- shorten the time needed to reexamine mips_get_saved_register()
when it finally does come time to reimplement or eliminate it.
Kevin