Documentation for memory tagging remote packets

Document the remote packet changes to support memory tagging.

gdb/doc/ChangeLog:

2021-03-24  Luis Machado  <luis.machado@linaro.org>

	* gdb.texinfo (General Query Packets): Document qMemTags and
	QMemTags.  Document the "memory-tagging" feature.
	(ARM-Specific Protocol Details): Document memory tag types.

gdb/doc/ChangeLog

@@ -1,3 +1,9 @@
+2021-03-24  Luis Machado  <luis.machado@linaro.org>
+
+	* gdb.texinfo (General Query Packets): Document qMemTags and
+	QMemTags.  Document the "memory-tagging" feature.
+	(ARM-Specific Protocol Details): Document memory tag types.
+
 2021-03-18  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* python.texinfo (Parameters In Python): Return empty string in

gdb/doc/gdb.texinfo

@@ -40992,6 +40992,87 @@ is a sequence of thread IDs, @var{threadid} (eight hex
 digits), from the target.  See @code{remote.c:parse_threadlist_response()}.
 @end table
 
+@item qMemTags:@var{start address},@var{length}:@var{type}
+@anchor{qMemTags}
+@cindex fetch memory tags
+@cindex @samp{qMemTags} packet
+Fetch memory tags of type @var{type} from the address range
+@w{@r{[}@var{start address}, @var{start address} + @var{length}@r{)}}.  The
+target is responsible for calculating how many tags will be returned, as this
+is architecture-specific.
+
+@var{start address} is the starting address of the memory range.
+
+@var{length} is the length, in bytes, of the memory range.
+
+@var{type} is the type of tag the request wants to fetch.  The type is a signed
+integer.
+
+Reply:
+@table @samp
+@item @var{mxx}@dots{}
+Hex encoded sequence of uninterpreted bytes, @var{xx}@dots{}, representing the
+tags found in the requested memory range.
+
+@item E @var{nn}
+An error occured.  This means that fetching of memory tags failed for some
+reason.
+
+@item @w{}
+An empty reply indicates that @samp{qMemTags} is not supported by the stub,
+although this should not happen given @value{GDBN} will only send this packet
+if the stub has advertised support for memory tagging via @samp{qSupported}.
+@end table
+
+@item QMemTags:@var{start address},@var{length}:@var{type}:@var{tag bytes}
+@anchor{QMemTags}
+@cindex store memory tags
+@cindex @samp{QMemTags} packet
+Store memory tags of type @var{type} to the address range
+@w{@r{[}@var{start address}, @var{start address} + @var{length}@r{)}}.  The
+target is responsible for interpreting the type, the tag bytes and modifying
+the memory tag granules accordingly, given this is architecture-specific.
+
+The interpretation of how many tags (@var{nt}) should be written to how many
+memory tag granules (@var{ng}) is also architecture-specific.  The behavior is
+implementation-specific, but the following is suggested.
+
+If the number of memory tags, @var{nt}, is greater than or equal to the
+number of memory tag granules, @var{ng}, only @var{ng} tags will be
+stored.
+
+If @var{nt} is less than @var{ng}, the behavior is that of a fill operation,
+and the tag bytes will be used as a pattern that will get repeated until
+@var{ng} tags are stored.
+
+@var{start address} is the starting address of the memory range.  The address
+does not have any restriction on alignment or size.
+
+@var{length} is the length, in bytes, of the memory range.
+
+@var{type} is the type of tag the request wants to fetch.  The type is a signed
+integer.
+
+@var{tag bytes} is a sequence of hex encoded uninterpreted bytes which will be
+interpreted by the target.  Each pair of hex digits is interpreted as a
+single byte.
+
+Reply:
+@table @samp
+@item OK
+The request was successful and the memory tag granules were modified
+accordingly.
+
+@item E @var{nn}
+An error occured.  This means that modifying the memory tag granules failed
+for some reason.
+
+@item @w{}
+An empty reply indicates that @samp{QMemTags} is not supported by the stub,
+although this should not happen given @value{GDBN} will only send this packet
+if the stub has advertised support for memory tagging via @samp{qSupported}.
+@end table
+
 @item qOffsets
 @cindex section offsets, remote request
 @cindex @samp{qOffsets} packet
@@ -41659,6 +41740,11 @@ These are the currently defined stub features and their properties:
 @tab @samp{-}
 @tab No
 
+@item @samp{memory-tagging}
+@tab No
+@tab @samp{-}
+@tab No
+
 @end multitable
 
 These are the currently defined stub features, in more detail:
@@ -41873,6 +41959,16 @@ The remote stub understands the @samp{QThreadEvents} packet.
 @item no-resumed
 The remote stub reports the @samp{N} stop reply.
 
+
+@item memory-tagging
+The remote stub supports and implements the required memory tagging
+functionality and understands the @samp{qMemTags} (@pxref{qMemTags}) and
+@samp{QMemTags} (@pxref{QMemTags}) packets.
+
+For AArch64 GNU/Linux systems, this feature also requires access to the
+@file{/proc/@var{pid}/smaps} file so memory mapping page flags can be inspected.
+This is done via the @samp{vFile} requests.
+
 @end table
 
 @item qSymbol::
@@ -42354,6 +42450,7 @@ details of XML target descriptions for each architecture.
 
 @menu
 * ARM Breakpoint Kinds::
+* ARM Memory Tag Types::
 @end menu
 
 @node ARM Breakpoint Kinds
@@ -42375,6 +42472,23 @@ These breakpoint kinds are defined for the @samp{Z0} and @samp{Z1} packets.
 
 @end table
 
+@node ARM Memory Tag Types
+@subsubsection @acronym{ARM} Memory Tag Types
+@cindex memory tag types, @acronym{ARM}
+
+These memory tag types are defined for the @samp{qMemTag} and @samp{QMemTag}
+packets.
+
+@table @r
+
+@item 0
+MTE logical tag
+
+@item 1
+MTE allocation tag
+
+@end table
+
 @node MIPS-Specific Protocol Details
 @subsection @acronym{MIPS}-specific Protocol Details