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Re: [patch/rfc,rfa:ppc64] Add osabi wildcard support
- From: Daniel Jacobowitz <drow at mvista dot com>
- To: gdb-patches at sources dot redhat dot com
- Date: Thu, 23 Oct 2003 19:41:50 -0400
- Subject: Re: [patch/rfc,rfa:ppc64] Add osabi wildcard support
- References: <3F986371.9060708@redhat.com>
On Thu, Oct 23, 2003 at 07:25:37PM -0400, Andrew Cagney wrote:
> Hello,
>
> The attached patch adds the ability to specify a wildcard machine when
> registering an OSABI / arch / machine. It then updates PPC64 GNU/Linux
> to specify that wild card (-1) instead of zero as the default machine.
>
> Looking at the PPC64 GNU/Linux code:
>
> gdbarch_register_osabi (bfd_arch_powerpc, 0, GDB_OSABI_LINUX,
> ppc_linux_init_abi);
>
> I believe that the call is attempting to register ppc_linux_init_abi as
> the OSABI handler for all arch/machine conbinations. The problem is
> that machine "0" gets turned into bfd_mach_ppc or bfd_mach_ppc64
> dependant on how GDB is built, and they are both incompatible with each
> other and incompatible . And that in turn restricts the support to just
> one half of the ISA family making it impossible for GDB to debug both 32
> and 64 bit :-(
>
> I know of two ways to fix this. First is the attached patch which
> modifies osabi.[hc] so that a wildcard machine (-1) can be specified vis:
>
> gdbarch_register_osabi (bfd_arch_powerpc, -1, GDB_OSABI_LINUX,
> ppc_linux_init_abi);
>
> and the second is to explicitly register both of these architecture
> variants vis:
>
> gdbarch_register_osabi (bfd_arch_powerpc, bfd_mach_ppc, ...
> gdbarch_register_osabi (bfd_arch_powerpc, bfd_mach_ppc64, ...
>
> (possibly also splitting ppc_linux_init_abi into ppc_linux_init_abi_32
> and ppc_linux_init_abi_32).
>
> There are pros and cons to both.
>
> The former will always match, making the code somewhat future proof, the
> later is far simplier.
>
> preferences?
My preference is for registering both. This is really a special case;
normally 0 is correct. It wouldn't have worked before but will with
Jim's recent change to can_run_code_for.
> Andrew
>
> PS: I'm also wondering if the existing ppc arch/machine table is
> complete. I think it will indicate that e500 is "compatible" with "ppc"
> when it is not.
The table is almost certainly not complete, but that's not the problem
here. The e500 is compatible with ppc - the e500 can run ppc code.
Vice versa is not necessarily true. There's a FIXME in osabi.c saying
that we should look for the most compatible architecture:
> type that is compatible with the desired machine type. Right
> now we simply return the first match, which is fine for now.
> However, we might want to do something smarter in the future. */
> - compatible = arch_info->compatible (arch_info, handler->arch_info);
> + compatible = info.bfd_arch_info->compatible (info.bfd_arch_info,
> + handler->arch_info);
> if (compatible == handler->arch_info)
> {
> (*handler->init_osabi) (info, gdbarch);
--
Daniel Jacobowitz
MontaVista Software Debian GNU/Linux Developer