Re: DWARF-2 and address sizes

[Andrew Cagney <ac131313@redhat.com>]

> On Fri, Jan 31, 2003 at 04:59:56PM -0500, Andrew Cagney wrote:
> 
>> >[Kevin, I noticed you doing some work in this area re S/390, maybe you've
>> >got a comment?  Anyone else?  I'm grasping at straws.]
>> >
>> >I'm trying to figure out how to handle addresses in the DWARF expression
>> >evaluator.  First consider DW_OP_deref: the following data is "the size of
>> >an address on the target machine", which I would personally take to mean
>> >cu_header->addr_size.  Is this ever different from TARGET_ADDRESS_BIT /
>> >TARGET_CHAR_BIT, which is what Daniel was originally using?
> 
>> 
>> I can imagine architectures wack-o enough for cu_header->addr_size != 
>> TARGET_ADDRESS_BIT / TARGET_CHAR_BIT.  Someone doing a 16 bit port using 
>> 32 bit elf.
> 
> 
> I wonder if MIPS64 Linux kernels do this, since they're technically
> ELF32?  Hmm, probably not.

Well, for ages elf32 was being used in MIPS64 with a 64 bit pointer.

>> >If the consensus is "no, that's too stupid to be allowed to live", then 
>> >this
>> >gets much easier.
>> >
>> >(Then consider DW_OP_deref_size; this is a fun one, since it has to be
>> >zero-extended to the size of an address on the target machine according to
>> >the spec, and then in GDB it may have to be zero or sign extended to the
>> >size of a CORE_ADDR for storage.  I haven't tested any of this on MIPS yet
>> >and I don't want to, damn it.  I don't know of any MIPS ABI with multiple
>> >pointer sizes, and you can't link different ABIs, so encountering
>> >DW_OP_deref_size is probably impossible.  I hope.)
> 
>> 
>> Have a look at dwarf2read.c:read_address() the existing code already 
>> handles one case of this.
> 
> 
> Yes.  I don't know if it sign extends properly in all cases - I guess
> it does if signed_address_p always matches whether a CORE_ADDR is a
> signed type, but that's dubious.

It sign extends sufficiently properly/often for it to at least appear to 
work.  Vis MIPS with 64 bit CORE_ADDR and registers but elf32.

Andrew