Re: [PATCH] [gdb/aarch64] pauth: Create new feature string for pauth to prevent crashing older gdb's

[Eli Zaretskii <eliz@gnu.org>]

> CC: <alex.bennee@linaro.org>, <richard.henderson@linaro.org>,
>  <peter.maydell@linaro.org>
> Date: Tue, 11 Apr 2023 23:43:27 +0100
> From: Luis Machado via Gdb-patches <gdb-patches@sourceware.org>
> 
> I've added some documentation to explain the situation.
> ---
>  gdb/aarch64-tdep.c  | 15 ++++++++++++++-
>  gdb/doc/gdb.texinfo | 16 ++++++++++++++++
>  2 files changed, 30 insertions(+), 1 deletion(-)

Thanks.

> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index 45a0580bc29..aefeb63f75c 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -47980,6 +47980,22 @@ has a signed link register value that needs to be unmasked/decoded.
>  Extra registers are allowed in this feature, but they will not affect
>  @value{GDBN}.
>  
> +Due to a bug in previous versions of @value{GDBN} (versions 9, 10, 11 and 12),
> +a new feature string was created to prevent targets causing a @value{GDBN}
> +crash whenever they reported support for Pointer Authentication and also
> +reported additional system registers that were not accounted for by
> +@value{GDBN}.  This is common when using emulators and on bare-metal debugging
> +scenarios.
> +
> +The new feature string is @samp{org.gnu.gdb.aarch64.pauth_v2}, and it has
> +the same contents as feature string @samp{org.gnu.gdb.aarch64.pauth}.
> +
> +Targets reporting Pointer Authentication support via the remote protocol
> +should always use the newer feature string @samp{org.gnu.gdb.aarch64.pauth_v2}.
> +
> +In the future the @samp{org.gnu.gdb.aarch64.pauth} feature string might be
> +deprecated in favor of @samp{org.gnu.gdb.aarch64.pauth_v2}.
> +

Since this is the manual for GDB users, it should describe the feature
first, and explain its use and rationale after that.  So this
description is backwards: it starts with the reason for introduction
of this feature, something that doesn't necessarily make sense to the
reader of the manual.

Instead, we should first say that 'org.gnu.gdb.aarch64.pauth' will be
deprecated in favor of 'org.gnu.gdb.aarch64.pauth_v2', then introduce
'org.gnu.gdb.aarch64.pauth_v2' saying that it has the same contents as
the former, and finally explain that targets should use
'org.gnu.gdb.aarch64.pauth_v2' to avoid the danger of crashing older
GDBs.

OK?

Reviewed-By: Eli Zaretskii <eliz@gnu.org>