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Re: extract_unsigned_integer API (Re: [PATCH] Remove MAX_REGISTER_SIZE from frame.c)
- From: Pedro Alves <palves at redhat dot com>
- To: Yao Qi <qiyaoltc at gmail dot com>
- Cc: Alan Hayward <Alan dot Hayward at arm dot com>, "gdb-patches at sourceware dot org" <gdb-patches at sourceware dot org>, nd <nd at arm dot com>
- Date: Tue, 28 Mar 2017 23:23:24 +0100
- Subject: Re: extract_unsigned_integer API (Re: [PATCH] Remove MAX_REGISTER_SIZE from frame.c)
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On 03/28/2017 05:57 PM, Pedro Alves wrote:
> Yes, and that can sorted by e.g., passing the size to the buffer()
> method, as I mentioned in the comment. Like:
>
> extractor extr;
> frame_unwind_register (frame, regnum, ext.buffer (size));
> return extr.extract (size, byte_order);
>
> extractor::buffer(size_t) would throw error on overflow.
>
> Or pass it to the ctor (which would likewise throw error on overflow):
>
> extractor extr (size);
> frame_unwind_register (frame, regnum, ext.buffer ());
> return extr.extract (size, byte_order);
>
> Could even store the size and byte order inside the extractor
> object, and avoid writing the size more than once:
>
> extractor extr (size, byte_order);
> frame_unwind_register (frame, regnum, ext.buffer ());
> return extr.extract ();
>
> Or make "extrator::buffer" remember the last size, so extractors
> can be reused. Or even support both, ctor with and without size,
> buffer() with and without size. extractror::extract would always
> used the last remembered size.
>
> So I still don't see any advantage in a callback-based interface.
Thinking about this a bit more, if we went this direction, I think the
simplest would be to add an extract::size() method that returned the
size of the buffer, and use that for bounds when filling in the
data, like:
extractor extr;
frame_unwind_register (frame, regnum, ext.buffer (), ext.size ());
return extr.extract (type_len, byte_order);
If type_len is larger than the buffer size, then we'll still get an
error either inside extractor::extract, and maybe earlier
inside frame_unwind_register (if it had that size parameter).
Though for the particular case of frame_unwind_register, since the
frame machinery works with struct value's, inside frame_unwind_register
there's going to be a value created already, and that has a contents
buffer we could access directly. So e.g.,
inside frame_unwind_register_signed, we should be able to use
frame_unwind_register_value directly thus avoid the need for the local
buffer and copying data.
Thanks,
Pedro Alves