[PATCH v5 23/25] Document new "x" and "print" memory tagging extensions

Luis Machado via Gdb-patches
2021-01-27T20:22:05Z

Document the changes to the "print" and "x" commands to support memory
tagging.

gdb/doc/ChangeLog:

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

* gdb.texinfo (Data): Document memory tagging changes to the "print"
command.
(Examining Memory): Document memory tagging changes to the "x"
command.
(Memory Tagging): Update with more information on changes to the "x"
and "print" commands.
---
gdb/doc/gdb.texinfo | 28 +++++++++++++++++++++++++---
1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index f751bdf4d3..5b21991b10 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -9935,6 +9935,10 @@ If you omit @var{expr}, @value{GDBN} displays the last value again (from the
conveniently inspect the same value in an alternative format.
@end table

+If the architecture supports memory tagging, the @code{print} command will
+display pointer/memory tag mismatches if what is being printed is a pointer
+or reference type. @xref{Memory Tagging}.
+
A more low-level way of examining data is with the @code{x} command.
It examines data in memory at a specified address and prints it in a
specified format. @xref{Memory, ,Examining Memory}.
@@ -10702,7 +10706,8 @@ number is specified, memory is examined backward from @var{addr}.
@item @var{f}, the display format
The display format is one of the formats used by @code{print}
(@samp{x}, @samp{d}, @samp{u}, @samp{o}, @samp{t}, @samp{a}, @samp{c},
-@samp{f}, @samp{s}), and in addition @samp{i} (for machine instructions).
+@samp{f}, @samp{s}), @samp{i} (for machine instructions) and
+@samp{m} (for displaying memory tags).
The default is @samp{x} (hexadecimal) initially. The default changes
each time you use either @code{x} or @code{print}.

@@ -10797,6 +10802,22 @@ counter is shown with a @code{=>} marker. For example:
0x804838c <main+24>: call 0x80482d4 <puts@@plt>
@end smallexample

+If the architecture supports memory tagging, the tags can be displayed by
+using @samp{m}. @xref{Memory Tagging}.
+
+The information will be displayed once per granule size
+(the amount of bytes a particular memory tag covers). For example, AArch64
+has a granule size of 16 bytes, so it will display a tag every 16 bytes.
+
+Due to the way @value{GDBN} prints information with the @code{x} command (not
+aligned to a particular boundary), the tag information will refer to the
+initial address displayed on a particular line. If a memory tag boundary
+is crossed in the middle of a line displayed by the @code{x} command, it
+will be displayed on the next line.
+
+The @samp{m} format doesn't affect any other specified formats that were
+passed to the @code{x} command.
+
@cindex @code{$_}, @code{$__}, and value history
The addresses and contents printed by the @code{x} command are not saved
in the value history because there is often too much of them and they
@@ -10874,8 +10895,9 @@ If the underlying architecture supports memory tagging, like AArch64 MTE
or SPARC ADI do, @value{GDBN} can make use of it to validate addresses and
pointers against memory allocation tags.

-A command prefix of @code{memory-tag} gives access to the various memory tagging
-commands.
+The @code{print} (@pxref{Data}) and @code{x} (@pxref{Memory}) commands will
+display tag information when appropriate, and a command prefix of
+@code{memory-tag} gives access to the various memory tagging commands.

The @code{memory-tag} commands are the following:

--
2.25.1