Re: [PATCH v2 1/4] gdb: aarch64: Remove MTE address checking from get_memtag

[Gustavo Romero <gustavo.romero@linaro.org>]

Hi Thiago,

On 3/29/24 9:55 PM, Thiago Jung Bauermann wrote:
> Thiago Jung Bauermann <thiago.bauermann@linaro.org> writes:
> 
>> Gustavo Romero <gustavo.romero@linaro.org> writes:
>>
>>> This commit removes aarch64_linux_tagged_address_p from
>>> aarch64_linux_get_memtag. aarch64_linux_tagged_address_p checks if an
>>> address is tagged (MTE) or not.
>>>
>>> The check is redundant because aarch64_linux_get_memtag is always called
>>> from the upper layers (i.e. from printcmd.c via gdbarch hook
>>> gdbarch_get_memtag) after either gdbarch_tagged_address_p (that already
>>> points to aarch64_linux_tagged_address_p) has been called or
>>> after should_validate_memtags (that calls gdbarch_tagged_address_p at
>>> the end) has been called, so the address is already checked. Hence:
>>>
>>> a) in print_command_1, aarch64_linux_get_memtag (via gdbarch_get_memtag
>>> hook) is called but only after should_validate_memtags, which calls
>>> gdbarch_tagged_address_p;
>>>
>>> b) in do_examine, aarch64_linux_get_memtag is also called only after
>>> gdbarch_tagged_address_p is directly called;
>>>
>>> c) in memory_tag_check_command, gdbarch_get_memtag is called -- tags
>>> matching or not -- after the initial check via direct call to
>>> gdbarch_tagged_address_p;
>>>
>>> d) in memory_tag_print_tag_command, address is checked directly via
>>> gdbarch_tagged_address_p before gdbarch_get_memtag is called.
>>
>> In cases c) and d), gdbarch_get_memtag gets called even if
>> gdbarch_tagged_address_p returns false, so won't this commit change the
>> behaviour of those functions in that case? I don't know enough about MTE
>> to be sure.
> 
> I just realised that in cases c) and d) an error will be thrown by
> show_addr_not_tagged if gdbarch_tagged_address_p returns false, so
> gdbarch_get_memtag doesn't get called in that case and my concern isn't
> valid. Sorry about that.

Yeah. No worries, I also missed that show_addr_not_tagged throws an error
the first time I read this part, it looked like just printing function :)


> Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>

Thanks for the review.


Cheers,
Gustavo