Re: GDB on SGI Irix 6.5

[Daniel Berlin <dan@cgsoftware.com>]

David B Anderson <davea@quasar.engr.sgi.com> writes:

>|
>|> From: Elena Zannoni <ezannoni@cygnus.com>
>|> Date: Tue, 12 Jun 2001 16:03:49 -0400
>|> 
>|> Andrew Cagney writes:
>|>  > [I'll take the liberty of adding Elena and Jim.  Might be useful to pose 
>|>  > any follow on questions on gdb@]
>|>  > 
>|>  > > On Thu, 17 May 2001, David B Anderson wrote:
>|>  > > 
>|>  > > 
>|>  > >> The 64bit dwarf2 that is read by read_initial_length is based on
>|>  > >> dwarf 2.1, designed in 2000.  SGI 64bit dwarf2 was designed in
>|>  > >> the early 1990's.  SGI made offsets etc 64bit in elf64
>|>  > >> (and offsets etc 32bits in elf32).    
>|>  > >> (basically we could not bring ourselves to limit dwarf 
>|>  > >> offsets to 32 bits in an elf64 file...)
>|>  > >> 
>|>  > >> Anyway,  to be correct for IRIX6,  read_initial_length
>|>  > >> needs to know it is IRIX elf64 and then
>|>  > >> /* UNTESTED, NOT ALL THAT NEEDS TO BE DONE probably */
>|>  > >> cu_header->initial_length_size = 8;
>|>  > >> cu_header->offset_size = 8;
>|>  > >> at least gives the right sizes.
>|>  > > 
>|>  > > 
>|> 
>|> Are these the only differences? Is anything SGI specific encoded in the
>|> 'version' field of cu_header? Maybe that can be used. Is there somewhere 
>|> in the debug info a field that tells that this is SGI's version?
>|
>|I don't see anything in the documents I got from Dave's site.  Dave,
>|could you please answer these questions?
>|
>|Thanks for the other advice, I will look that up.
> 
> Hopefully already anwered. No, other field in dwarf2.
> 
> However, because IRIX is big-endian, and because no
> compilation unit should have an
> 	initial-length
> field with all zero bits,
> 
> A test for a dwarf2 CU (compilation unit) 
> initial-length of zero followed 4 bytes
> later by a correct version number for dwarf2
> might suffice (in an elf64 big endian object) folowed by setting
> up the initial_length_size and offset_size 
> as above might suffice.

This is correct.  The initial length should never be zero.  Even for
64 bit dwarf 2.1, it's 0xffffffff followed by 8 bytes of the real
initial length.


> 
> Whether this can be done sensibly multi-arch in gdb is not clear to me.
> 
> davea@sgi.com

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