Re: [PATCH v5 03/25] Add GDB-side remote target support for memory tagging

[Simon Marchi via Gdb-patches <gdb-patches@sourceware.org>]

On 2021-01-27 3:20 p.m., Luis Machado via Gdb-patches wrote:
> Updates for v4:
> 
> - Rename RSP helper functions.
> - Fixup parameter and return types.
> 
> Updates for v2:
> 
> - Add type field to target hooks.
> - Add type data to qMemTags and QMemTags. The packets now look like this:
> 
> qMemTags:<address>,<length>:<type>
> QMemTags:<address>,<length>:<type>:<uninterpreted tag bytes>
> 
> --
> 
> This patch adds memory tagging support to GDB's remote side, with
> packet string checks, new packet support and an implementation of
> the two new tags methods fetch_atags and store_atags.

fetch_memtags and store_memtags

> 
> GDBserver needs to know how to read/write allocation tags, since that is
> done via ptrace.  It doesn't need to know about logical tags.
> 
> The new packets are:
> 
> qMemTags:<address>,<length>:<type>
> --
> 
> Reads tags of the specified type from the address range
> [<address>, <address + length>)
> 
> QMemTags:<address>,<length>:<type>:<uninterpreted tag bytes>
> --
> Writes the tags of specified type represented by the uninterpreted bytes to
> the address range [<address>, <address + length>).
> 
> The interpretation of what to do with the tag bytes is up to the arch-specific
> code.
> 
> Note that these new packets consider the case of packet size overflow as an
> error, given the common use case is to read/write only a few memory tags at
> a time.  Having to use a couple new packets for multi-part transfers wouldn't
> make sense for the little use it would have.
> 
> gdb/ChangeLog:
> 
> YYYY-MM-DD  Luis Machado  <luis.machado@linaro.org>
> 
> 	* remote.c (PACKET_memory_tagging_feature): New enum.
> 	(remote_memory_tagging_p): New function.
> 	(remote_protocol_features): New "memory-tagging" entry.
> 	(remote_target::remote_query_supported): Handle memory tagging
> 	support.
> 	(remote_target::supports_memory_tagging): Implement.
> 	(create_fetch_memtags_request, parse_fetch_memtags_reply)
> 	(create_store_memtags_request): New functions.
> 	(remote_target::fetch_memtags): Implement.
> 	(remote_target::store_memtags): Implement.
> 	(_initialize_remote): Add new "memory-tagging-feature"
> 	config command.
> ---
>  gdb/remote.c | 106 +++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 103 insertions(+), 3 deletions(-)
> 
> diff --git a/gdb/remote.c b/gdb/remote.c
> index b130f1ddae..bb3473b04c 100644
> --- a/gdb/remote.c
> +++ b/gdb/remote.c
> @@ -2175,6 +2175,10 @@ enum {
>    /* Support TARGET_WAITKIND_NO_RESUMED.  */
>    PACKET_no_resumed,
>  
> +  /* Support for memory tagging, allocation tag fetch/store
> +     packets and the tag violation stop replies.  */
> +  PACKET_memory_tagging_feature,
> +
>    PACKET_MAX
>  };
>  
> @@ -2316,6 +2320,14 @@ remote_exec_event_p (struct remote_state *rs)
>    return packet_support (PACKET_exec_event_feature) == PACKET_ENABLE;
>  }
>  
> +/* Returns true if memory tagging is supported.  */
> +
> +static bool
> +remote_memory_tagging_p (void)

Remove `void`.

Otherwise, LGTM.

Simon