Re: [PATCH v2 2/4] gdb: aarch64: Move MTE address check out of set_memtag

[Thiago Jung Bauermann <thiago.bauermann@linaro.org>]

Gustavo Romero <gustavo.romero@linaro.org> writes:

> On 3/29/24 9:47 PM, Thiago Jung Bauermann wrote:
>> Gustavo Romero <gustavo.romero@linaro.org> writes:
>>
>>> Move MTE address check out of set_memtag and add this check to the
>>> upper layer, before set_memtag is called. This is a preparation for
>>> using a target hook instead of a gdbarch hook MTE address checks.
>> gdbarch_set_memtags is also called from
>> memory_tag_with_logical_tag_command. Shouldn't the same check be added
>> there?
>
> In aarch64_linux_set_memtags, the memory check is inside the else {}, which
> is only executed when tag_type == memtag_type::allocation, but not in the if {},
> which is executed when memtag_type::logical. Because
> memory_tag_with_logical_tag_command always calls set_memtags with the argument
> for tag_type param == memtag_type::logical there is no need to check the address.
>
> In other words, memory_tag_with_logical_tag_command is about logical tags only,
> so it's a local operation that does not touch any memory in the target, it just
> changes a local pointer, so it's ok to change the pointer, being it tagged or not,
> hence not memory checks are needed.
>
> These comments try to clarify a bit it:
>
> In memory_tag_with_logical_tag_command:
>
>   /* Setting the logical tag is just a local operation that does not touch
>      any memory from the target.  Given an input value, we modify the value
>      to include the appropriate tag.  <--
>
>
> In memory_tag_print_tag_command:
>
>   /* If the address is not in a region memory mapped with a memory tagging
>      flag, it is no use trying to access/manipulate its allocation tag.
>
>      It is OK to manipulate the logical tag though.  */ <--

Thanks for the explanation, makes sense!

--
Thiago