Re: [PATCH v3 1/7] gdb: aarch64: Remove MTE address checking from get_memtag

[Luis Machado <luis.machado@arm.com>]

On 4/4/24 07:48, Gustavo Romero wrote:
> 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.
> 
> Also, because after this change the address checking only happens at the
> upper layer it now allows the address checking to be specialized easily
> per target, via a target hook.
> 
> Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
> ---
>  gdb/aarch64-linux-tdep.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
> index 0b9784f38e4..50055ac3f48 100644
> --- a/gdb/aarch64-linux-tdep.c
> +++ b/gdb/aarch64-linux-tdep.c
> @@ -2575,10 +2575,6 @@ aarch64_linux_get_memtag (struct gdbarch *gdbarch, struct value *address,
>      tag = aarch64_mte_get_ltag (addr);
>    else
>      {
> -      /* Make sure we are dealing with a tagged address to begin with.  */
> -      if (!aarch64_linux_tagged_address_p (gdbarch, address))
> -	return nullptr;
> -
>        /* Remove the top byte.  */
>        addr = gdbarch_remove_non_address_bits (gdbarch, addr);
>        std::optional<CORE_ADDR> atag = aarch64_mte_get_atag (addr);

Thanks. This is OK and can go in separately, or alongside the rest of the series if you wish.

Approved-By: Luis Machado <luis.machado@arm.com>
Tested-By: Luis Machado <luis.machado@arm.com>