Re: [PATCH] should_validate_memtags: Do not dereference references

[Kevin Buettner <kevinb@redhat.com>]

On Fri,  1 Aug 2025 09:39:43 -0700
Keith Seitz <keiths@redhat.com> wrote:

> should_validate_memtags uses value_as_address to evalute
> whether an address for a value is tagged. The comments for
> that function simply say, "Extract a value as a C pointer."
> 
> While that sounds innoncuous, that function calls coerce_array,
> which will dereference any references.  This is not what is
> desired here.
> 
> This can be demonstrated on an MTE-enabled host, such as aarch64-
> based Ampere (example taken from tests introduced in this patch):
> 
> (gdb) p b.get_foo ()
> Could not validate memory tag: Value can't be converted to integer.
> $2 = (const foo &) @0xffffffffed88: {m_a = 42}
> 
> While the command completes, gdb didn't actually attempt to
> evaluate any memory tags.
> 
> Fix this by using unpack_pointer instead.
> 
> Tested on x86_64 Fedora 40 and aarch64 RHEL 9.6.
> ---
>  gdb/printcmd.c                             |  4 +-
>  gdb/testsuite/gdb.cp/method-ref-return.cc  | 42 +++++++++++++
>  gdb/testsuite/gdb.cp/method-ref-return.exp | 70 ++++++++++++++++++++++
>  gdb/value.c                                |  0
>  4 files changed, 115 insertions(+), 1 deletion(-)
>  create mode 100644 gdb/testsuite/gdb.cp/method-ref-return.cc
>  create mode 100644 gdb/testsuite/gdb.cp/method-ref-return.exp
>  mode change 100644 => 100755 gdb/value.c

Aside from the mode change of gdb/value.c, this LGTM.  Approved, with
that change undone...

Approved-by: Kevin Buettner <kevinb@redhat.com>