Re: [PATCH 1/6] symbols: add minimal self-test

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 13/03/2025 1:52 pm, Jan Beulich wrote:
> ... before making changes to the involved logic.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> With this FAST_SYMBOL_LOOKUP may make sense to permit enabling even
> when LIVEPATCH=n. Thoughts? (In this case "symbols: centralize and re-
> arrange $(all_symbols) calculation" would want pulling ahead.)
>
> --- a/xen/common/symbols.c
> +++ b/xen/common/symbols.c
> @@ -260,6 +260,41 @@ unsigned long symbols_lookup_by_name(con
>      return 0;
>  }
>  
> +#ifdef CONFIG_SELF_TESTS
> +
> +static void __init test_lookup(unsigned long addr, const char *expected)
> +{
> +    char buf[KSYM_NAME_LEN + 1];
> +    const char *name, *symname;
> +    unsigned long size, offs;
> +
> +    name = symbols_lookup(addr, &size, &offs, buf);
> +    if ( !name )
> +        panic("%s: address not found\n", expected);
> +    if ( offs )
> +        panic("%s: non-zero offset (%#lx) unexpected\n", expected, offs);
> +
> +    /* Cope with static symbols, where varying file names/paths may be used. 
> */
> +    symname = strchr(name, '#');
> +    symname = symname ? symname + 1 : name;
> +    if ( strcmp(symname, expected) )
> +        panic("%s: unexpected symbol name: '%s'\n", expected, symname);
> +
> +    offs = symbols_lookup_by_name(name);
> +    if ( offs != addr )
> +        panic("%s: address %#lx unexpected; wanted %#lx\n",
> +              expected, offs, addr);
> +}
> +
> +static void __init __constructor test_symbols(void)
> +{
> +    /* Be sure to only try this for cf_check functions. */

I'm very happy to see the take-up of SELF_TESTs.  Although I probably
ought to tie it into a Kconfig option to make the errors non-fatal,
which I've been meaning to do for a bit.

One question though.  cf_check is an x86-ism, even if it leaks out into
common code.

I think you mean "functions emitted into the final image"?  If so, I
don't think this is relevant then, because ...

> +    test_lookup((unsigned long)dump_execstate, "dump_execstate");
> +    test_lookup((unsigned long)test_symbols, __func__);

... taking the function address here forces it to be emitted even if it
would otherwise have been inlined.

~Andrew