From: Andrew Cagney <ac131313@redhat.com>
To: Doug Evans <dje@transmeta.com>
Cc: gdb@sources.redhat.com
Subject: Re: Inferior function call command set
Date: Thu, 01 May 2003 22:48:00 -0000 [thread overview]
Message-ID: <3EB1A43B.1040704@redhat.com> (raw)
In-Reply-To: <16049.38488.94378.161876@casey.transmeta.com>
> Andrew Cagney writes:
> > > Out of curiousity, is there any need to have a runtime choice?
> >
> > Entry point in ROM, non 1:1 code/stack, ...
>
> Apologies, still confused.
> [having spent the last few days buried in the guts of
> hand-called-function support such things are very much on my
> mind these days]
>
> How does having an entry point in ROM affect things?
> It appears to me that all AT_ENTRY_POINT does is use the entry point
> address as a magic number that will "never appear" in user code.
> [thus if the callee is returning to it you know you're back in the "stub"]
GDB tries to insert a breakpoint at that address (that doesn't work when
it is in a ROM :-) Looking at the MIPS, it turned out to also not work
very well when the entry point couldn't be found.
> In my port I added the ability for the user to override
> CALL_DUMMY_ADDRESS since the entry point is ambiguous/unspecified.
> [THAT would be a very welcome addition to the mainline code. :-)]
> Pproviding both AT_ENTRY_POINT and ON_STACK is _far_ more effort than
> providing the ability to override what gdb uses for CALL_DUMMY_ADDRESS.
> Perhaps what I should have done is just hardwire it to 42. 1/2 :-).
That isn't true.
For an up-to-date architecture, assuming the stack is executable(1),
there should be zero change. In fact, given problems with finding the
entry point address, on-stack is technically a better choice (although a
quick reality-check will stop that change dead). The d10v's tweak and
the retention of entry_point_address, stem from it being a true harvard
architecture.
A survey of architectures explicitly setting call_dummy_address reveals:
alpha: does something slightly weird (that may now be redundant)
avr: wrapped entry_point_address
m68hc11: wrapped entry_point_address
mips: wrapped entry_point_address, but with a hack for ROMs made
redundant by ``set call breakpoint-location on-stack''
sparc: depending on a compile time option, uses either
entry_point_address or the stack
so CALL_DUMMY_ADDRESS can/should probably be wired to entry_point_address.
> No claim is made that there isn't a need for the runtime
> stack/entry-point choice. But I still don't understand the need for it.
> [Not that anyone has to spend time clearing up my understanding of course;
> but if it's not that much effort, or if other people are also curious ...]
>
> > An addition to the testsuite is implicit.
Andrew
(1) Someone needs to get this working when the stack isn't executable.
The inferior would stop with a sigseg instead of sigtrap.
next prev parent reply other threads:[~2003-05-01 22:48 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-05-01 20:55 Andrew Cagney
2003-05-01 21:12 ` Doug Evans
2003-05-01 21:28 ` Andrew Cagney
2003-05-01 21:49 ` Doug Evans
2003-05-01 22:48 ` Andrew Cagney [this message]
2003-05-01 23:00 ` Doug Evans
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