From: Matthew Fortune <Matthew.Fortune@imgtec.com>
To: Andreas Arnez <arnez@linux.vnet.ibm.com>,
"gcc@gcc.gnu.org" <gcc@gcc.gnu.org>,
"gdb@sourceware.org" <gdb@sourceware.org>
Cc: Ulrich Weigand <uweigand@de.ibm.com>,
Maciej Rozycki <Maciej.Rozycki@imgtec.com>
Subject: RE: [RFC] DW_OP_piece vs. DW_OP_bit_piece on a Register
Date: Mon, 25 Jan 2016 22:01:00 -0000 [thread overview]
Message-ID: <6D39441BF12EF246A7ABCE6654B023536A70637C@LEMAIL01.le.imgtec.org> (raw)
In-Reply-To: <m3vb6wm86q.fsf@oc1027705133.ibm.com>
Andreas Arnez <arnez@linux.vnet.ibm.com> writes:
> 6 Summary of Open Questions
> ===========================
>
> 1. Out of the standard interpretations discussed under "options"
> (section 4) above, which do we want to settle on? Or is the
> "preferred" interpretation missing from that list?
> 2. Should pieces fully or partially outside their underlying objects
> be considered valid or invalid? If valid, how should they be
> aligned and padded? In any case, what is the suggested treatment
> by a DWARF consumer?
My dwarf knowledge is not brilliant but I have had to recently consider
it for MIPS floating point ABI changes aka FPXX and friends. I don't know
exactly where this fits in to your whole description but in case it has
a bearing on this we now have the following uses of DW_OP_piece:
1) double precision data split over two 32-bit FPRs
Uses a pair of 32-bit DW_OP_piece (ordered depending on endianness).
2) double precision data in one 64-bit FPR
No need for DW_OP_piece.
3) double precision data that may be in two 32-bit FPRs or may be in
one 64-bit FPR depending on hardware mode
Uses a single 64-bit DW_OP_piece on the even numbered register.
I'm guilty of not actually finishing this off and doing the GDB side but
the theory seemed OK when I did it! From your description this behaviour
best matches DW_OP_piece having ABI dependent behaviour which would make
it acceptable. These three variations can potentially exist in the same
program albeit that (1) and (3) can't appear in a single shared library
or executable. It's all a little strange but the whole floating point
MIPS o32 ABI is pretty complex now.
Matthew
next prev parent reply other threads:[~2016-01-25 22:01 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-14 16:34 Andreas Arnez
2016-01-16 13:27 ` Joel Brobecker
2016-01-18 16:00 ` Andreas Arnez
2016-01-25 22:01 ` Matthew Fortune [this message]
2016-01-26 11:57 ` Andreas Arnez
2016-02-11 12:18 ` Matthew Fortune
2016-02-11 17:04 ` Andreas Arnez
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