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Re: Architectures and Machine Names
- From: Doug Evans <dje at sebabeach dot org>
- To: jeremy dot bennett at embecosm dot com
- Cc: cgen at sourceware dot org
- Date: Mon, 24 Aug 2009 17:21:06 -0700
- Subject: Re: Architectures and Machine Names
- References: <1250877079.10529.224.camel@thomas>
Jeremy Bennett wrote:
I'm updating the OpenRISC 1000 binutils port and CGEN specification and
need some advice on defining architecture and machine.
Over the years there has been some confusion over naming with the
OpenRISC project. The OpenRISC 1000 is an architecture permitting
various implementations (32-bit, 64-bit, big-endian, little-endian).
Within this architecture there is a core instruction set (either 32 or
64-bit), and supplementary instruction sets for floating point and
vector operations.
Currently there is one 32-bit big-endian implementation, the OpenRISC
1200 supporting the core 32-bit instruction set
So it seems natural to define the CGEN architecture as or1k, with a
machine named or32 (supporting the core ISA) and a model named or1200.
All in a file named or1k.cpu.
Seems straightforward enough to me.
Users build their binutils using --target=or32-opencores-elf. I have a
BFD architecture bfd_arch_or1k and a BFD machine bfd_mach_or32.
Having --target=or32-foo is ok of course, but OOC did you want to have
one set of tools support all variants instead? E.g. have
--target=or1k-foo instead? You could have both, and only support
or1k-foo later of course. Just wondering.
However I am struggling to get binutils to accept the idea that the
machine name and architecture are different. CGEN will generate my
opcodes files using the architecture (or1k-) as prefix. However GAS will
set the prefix from the CPU (or32), not the CPU Type (or1k), so looks
for opcodes files with a or32- prefix.
This may just be a consequence of never having a port that did it this
way before, and we just need to spiff up things a bit. I.e. see above.
Looking through src/opcodes/Makefile.am, I see all cgen ports passing
the same text for arch= and prefix= to run-cgen.
OTOH, let's make sure you *want* to do it this way (i.e. have
--target=or32-foo instead of --target=or1k-foo). [Assuming I'm
understanding the issue correctly, that's not a given. :-)]
[And for my own education, does this mean the openrisc target is going away?
e.g. grep for openrisc in src/*/configure.in]
I have tried overriding this in configure.in for gas by setting the
prefix to match the CPU type (or1k), and binutils will build. However
the ELF images created by the assembler use the machine name (or32) as
the architecture, but the disassembler checks that the file matches the
architecture (or1k). Thus objdump -d will not recognize files created by
the assembler.
I'm not clear on what "use the machine name (or32) as the architecture"
means. Can you give details? E.g. example output from objdump -f or
some such? [objdump -f output mightn't be sufficient, all the details
you can provide will help]
The setting of architecture and machine name in the ELF files is mostly
a gas/bfd thing (IIRC). I'm not sure how cgen comes into play here.
Unfortunately I cannot find an example to follow within binutils of an
architecture like this. The SuperH processors are specified with CGEN
(sh.cpu), but not built with CGEN. All the CGEN targets in configure.in
with using_cgen=yes have the same name for both architecture and
machine.
I'd appreciate advice on how to resolve this. Most of the OpenRISC 1000
is common to all implementations, so it makes sense to have a single
"or1k" set of tools. However the user also needs to specify which CPU
within the "or1k" set, to allow variations to happen.
Many thanks,
Jeremy
Typically (for some definition of "typically" :-)) users have one set of
tools that handles all machine variants and they specify either in the
assembler file, or in parameters passed to gas, which machine variant
they are assembling for. No claim is made that this definition of
"typically" is, umm, typical. :-)
btw, if one were go with --target=or32-foo, and I'm not saying it's a
bad route to go, I'd pass the machine name to the -m option to cgen so
that only that machine's description is kept (and all others are
discarded). I see src/opcodes/cgen.sh currently passes "all" for -m,
we'd want to make that a parameter. Since it's always been "all",
getting this to work may involve a bit of hacking. Getting the
architecture/machine data right in the ELF file should be straightforward.
Can you send me a patch or tarball or some such for me to play with?