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Re: [PATCH v2 02/10] Add Aarch64 SVE Linux headers


On 06/12/2018 04:06 PM, Simon Marchi wrote:
> On 2018-06-12 10:43, Pedro Alves wrote:
>> What's "this" ?
> 
> From what I understand, "this" is the suggestion I made in my previous mail, require the user to build against the headers of a recent kernel (that provide the SVE macros), and not provide a stop-gap copy in the GDB tree.  It would break the buildbot, because they have an old kernel that doesn't provide the SVE macros the GDB code uses (e.g. SVE_PT_REGS_OFFSET).

OK, that was not what I had suggested the other day (which was to detect SVE
support at configure time), so I got confused.

> 
>> How about we add a configure check to check if the system headers support
>> the needed SVE bits, and guard the native gdb SVE bits with
>> HAVE_AARCH64_SVE or something like that?
> 
> I think that would be a good compromise.  By default, building on a machine with an older kernel would exclude SVE support.  But it would be possible to add it by pointing to the headers of a recent kernel.  So when building on a machine with an older kernel...
> 
> - ... without any special flags, you don't get SVE support.
> - ... with just --enable-sve, you get a configure error.
> - ... with --enable-sve and CFLAGS/CXXFLAGS pointing to headers of a kernel w/ SVE macros, you get SVE support.
> 
> Does that make sense?
Yes.  Not sure an --enable-sve switch is necessary (compared to just having
headers vs not having headers), but I'd be fine with having one.

Thanks,
Pedro Alves


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