Re: [PATCH v3] xen/console: print Xen version via keyhandler

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.02.2025 22:41, dmkhn@xxxxxxxxx wrote:
> Add Xen version printout to 'h' keyhandler output.
> 
> That is useful for debugging systems that have been left intact for a long
> time.
> 
> Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
> ---
> Changes since v2:
> - moved new function declarations to xen/lib.h
> - dropped xen_ prefix in new functions
> ---
>  xen/common/keyhandler.c    |  4 ++++
>  xen/common/version.c       | 20 ++++++++++++++++++--
>  xen/drivers/char/console.c |  8 +++-----
>  xen/include/xen/lib.h      |  3 +++
>  4 files changed, 28 insertions(+), 7 deletions(-)
> 
> diff --git a/xen/common/keyhandler.c b/xen/common/keyhandler.c
> index 6ea54838d4..0bb842ec00 100644
> --- a/xen/common/keyhandler.c
> +++ b/xen/common/keyhandler.c
> @@ -129,6 +129,10 @@ static void cf_check show_handlers(unsigned char key)
>      unsigned int i;
>  
>      printk("'%c' pressed -> showing installed handlers\n", key);
> +
> +    print_version();
> +    print_build_id();
> +
>      for ( i = 0; i < ARRAY_SIZE(key_table); i++ )
>          if ( key_table[i].fn )
>              printk(" key '%c' (ascii '%02x') => %s\n",
> diff --git a/xen/common/version.c b/xen/common/version.c
> index bc3714b45f..8672d5544e 100644
> --- a/xen/common/version.c
> +++ b/xen/common/version.c
> @@ -210,9 +210,25 @@ void __init xen_build_init(void)
>          }
>      }
>  #endif /* CONFIG_X86 */
> -    if ( !rc )
> -        printk(XENLOG_INFO "build-id: %*phN\n", build_id_len, build_id_p);
>  }
> +
> +void print_version(void)
> +{
> +    printk("Xen version %d.%d%s (%s@%s) (%s) %s %s\n",
> +           xen_major_version(), xen_minor_version(), xen_extra_version(),
> +           xen_compile_by(), xen_compile_domain(), xen_compiler(),
> +           xen_build_info(), xen_compile_date());
> +
> +    printk("Latest ChangeSet: %s\n", xen_changeset());
> +}
> +
> +void print_build_id(void)
> +{
> +    BUG_ON(!build_id_p);
> +    BUG_ON(!build_id_len);

Technically one of the two would likely suffice, if we need such checks
at all. Question is why you added them. After all ...

> +    printk(XENLOG_INFO "build-id: %*phN\n", build_id_len, build_id_p);

... this isn't supposed to malfunction when passed a NULL pointer (with
zero length). If it can malfunction, it wants fixing there imo. And that
extends to the case of non-zero length as well: Any extensions to %p
that we add would better retain the basic property of %p printing when
NULL is passed as argument. (I'm sorry for not paying enough attention
to this on v2 already.)

(Later) Oh, actually these BUG_ON() are both wrong. They would trigger
when building with a build-id-incapable linker. See the detection logic
in the top level Makefile (search for XEN_HAS_BUILD_ID). To retain
original behavior you will want to make the printk() conditional upon
e.g. build_id_len being non-zero.

Jan