Re: [PATCH 4/8] Enable SVE for GDB

[Alan Hayward <Alan.Hayward@arm.com>]

> On 31 May 2018, at 15:59, Pedro Alves <palves@redhat.com> wrote:
> 
> On 05/11/2018 11:52 AM, Alan Hayward wrote:
>> --- a/gdb/aarch64-tdep.c
>> +++ b/gdb/aarch64-tdep.c
>> @@ -2873,6 +2873,26 @@ aarch64_read_description (long vq)
>>   return tdesc;
>> }
>> 
>> +/* Return the VQ used when creating the target description TDESC.  */
>> +
>> +static long
>> +aarch64_get_tdesc_vq (const struct target_desc *tdesc)
> 
> Is this use of "long" significant?  I mean, is it assuming 64-bit?
> I ask because longs are not 64-bit on x64 Windows, so it would
> do the wrong thing when cross debugging.

In the kernel structure it’s a 16bit value.

However, the VG "register" in the regcache is a 64bit value. (It’s not
a real system register, but helps a great deal to see it as one in gdb,
and we need it as a dwarf register.) I made it 64bits to match the
minimum size of all the other aarch64 registers.
I did have it as 16bits at one point, but it went wrong when using it
with dwarf as it expects all the dwarf registers to be the minimum
register.

I chose to do the conversion from 16bits to 64bits at the point vg is
read from the kernel. This makes the code easy as from then on as it’s
always 64bits throughout.

Alternatively, I could have kept as 16bits up to the point it hits
the regcache. But that leaves two different types around the code.


Alan.