[PATCH v2 07/24] Documentation for memory tagging remote packets

Luis Machado via Gdb-patches
2020-10-22T20:00:47Z

Updates on v2:

- Update documentation to mention the packet's type field.

--

Document the remote packet changes to support memory tagging.

gdb/doc/ChangeLog:

YYYY-MM-DD Luis Machado <luis.machado@linaro.org>

* gdb.texinfo (General Query Packets): Document qMemTags and
QMemTags.
Document the "memory-tagging" feature.
---
gdb/doc/gdb.texinfo | 90 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 90 insertions(+)

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 2636b6f990..b778e48dd4 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -40762,6 +40762,83 @@ 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}
+@cindex fetch memory tags
+@cindex @samp{qMemTags} packet
+Fetch memory tags of type @var{type} from the address range
+@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, a signed integer, the request wants to fetch.
+
+Reply:
+@table @samp
+@item @var{mxx}@dots{}
+Hex encoded sequence of uninterpreted bytes, @var{xx}@dots{}, representing the
+tags found in the request 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}
+@cindex store memory tags
+@cindex @samp{QMemTags} packet
+Store memory tags of type @var{type} to the address range
+@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 should be written to how many memory tag
+granules 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, a signed integer, the request wants to store.
+
+@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
@@ -41429,6 +41506,11 @@ 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:
@@ -41643,6 +41725,14 @@ 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} and @samp{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::
--
2.17.1