Re: [PATCH 0/3 v3] [AArch64] Support tagged pointer

Simon Marchi
2018-04-11T02:46:28Z

On 2018-04-10 20:36, Omair Javaid wrote:
>> This patch has broken kernel debugging using kgdb and openOCD.
>>
>> Tagged address should only be considered while debugging only
>> user-space
>> programs on linux.
>>
>> I still need to understand the full background behind this patch but
>> can
>> we pull it out of 8.1 release to make sure kernel debugging works?
>>
>>
> Just found out that patch series posted here
> https://sourceware.org/ml/gdb-patches/2017-12/msg00160.html does change
> aarch64-linux-tdep only.
> But the committed version here
> https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=a738ea1d41daeec0cccb4ab6671f4f6d53bd9e18
> is
> applying it to aarch64-tdep

I think it was because of Pedro's suggestion in this reply:
https://sourceware.org/ml/gdb-patches/2017-12/msg00179.html

although there was now acknowledgement from Yao, so I can only guess.

As Pedro said, it's the hardware that ignores these top bits. But it
first has to be configured to do so, so we can't assume that all aarch64
code behaves like this. So far we only know that the Linux userspace
threads work like that, so I think it would make sense to move it to
aarch64-linux-tdep.c. Did you confirm that it indeed fixes your
problem?

I could see a fix for this getting into the 8.1 branch (not reverting
the patch though).

Simon