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Re: [rfc/patch] extract/store typed floating ()
- To: Mark Kettenis <kettenis at science dot uva dot nl>
- Subject: Re: [rfc/patch] extract/store typed floating ()
- From: Andrew Cagney <ac131313 at cygnus dot com>
- Date: Sun, 23 Sep 2001 16:06:35 -0400
- Cc: gdb-patches at sources dot redhat dot com
- References: <3BAA6F4A.1000508@cygnus.com> <s3i7kuqc9u5.fsf@soliton.wins.uva.nl>
>
> I'm not sure whether zeroing out the buffer in store_typed_floating()
> is desirable. I've (almost) convinced myself that it isn't. Here's a
> part of a comment that I added to the doublest.c in my current tree:
>
> /* ...
>
> It is debatable whether we should zero out any remaining
> bytes in the target buffer, when converting from a type that
> has a smaller length than the target type. Right now we
> don't do that. A typical case where this situation arises is
> when we convert a i387 floating-point register to a `long
> double' in memory. On the target, that operation only stores
> the first 10 bytes, and leaves alone the remaining 2 bytes.
> It makes sense to mimick this behaviour here. */
>
> This comment comes from a function convert_floating() that I intend to
> add to doublest.c. I'll submit a patch after you've checked yours in.
Don't forget that the routines are expecting to manipulate a GDB
internal buffer freshly allocated from the heap and not target memory.
Failing to initialize it would leave it containing complete garbage
(perhaphs I should set it to 0xdeadbeef). That garbage would then be
written back to the target since (well from memory) GDB writes all
length bytes from a value buffer.
To ``do the write thing'', I suspect ``struct value'' and the value <->
memory transfer routines would all need to be modified so that they only
write a sub-section of the buffer. Other ideas also come to mind:
edit_typed_floating() that edits an floating point buffer in place; add
an ``old buffer'' parameter that can be used to optionally initialize
unused bytes; or use the raw floatformat routines(1) where needed.
The case that would worry me is with i387 registers. For that, I think
the target should just specify the 10 byte FP type so that GDB won't
touch any padding bytes.
Andrew
(1) Would need to fix the problem of TYPE_FLOATFORMAT not always being
initialized.