Re: [PATCH 07/10] x86/ucode: Move the CPIO path string into microcode_ops

[Jan Beulich <jbeulich@xxxxxxxx>]

On 28.10.2024 10:18, Andrew Cooper wrote:
> We've got a perfectly good vendor abstraction already for microcode.  No need
> for a second ad-hoc one in microcode_scan_module().
> 
> This is in preparation to use ucode_ops.cpio_path in multiple places.
> 
> These paths are only used during __init, so take the opportunity to move them
> into __initconst.

As an alternative to this, how about ...

> --- a/xen/arch/x86/cpu/microcode/private.h
> +++ b/xen/arch/x86/cpu/microcode/private.h
> @@ -59,6 +59,13 @@ struct microcode_ops {
>       */
>      enum microcode_match_result (*compare_patch)(
>          const struct microcode_patch *new, const struct microcode_patch 
> *old);
> +
> +    /*
> +     * For Linux inird microcode compatibliity.
> +     *
> +     * The path where this vendor's microcode can be found in CPIO.
> +     */
> +    const char *cpio_path;

    const char cpio_path[];

inheriting the __initconst from the struct instances?
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
with a slight preference to the form without the extra pointer. Except that:
gcc14 looks to be buggy when it comes to the copying of such a struct. The
example below yields an internal compiler error. And the direct structure
assignment also doesn't quite do what I would expect it to do (visible when
commenting out the "else" branch. Bottom line - leave the code as is.

Jan

struct s {
        unsigned long ul;
        int i;
        char ac[];
};

const struct s gs = { 3, -4, "abcdef" };

void copy_s(struct s*d, const struct s*s) {
        *d = *s;
}

unsigned test(struct s*ps, _Bool direct) {
        if(direct)
                *ps = gs;
        else
                copy_s(ps, &gs);
        return sizeof(*ps);
}

unsigned size(void) {
        return sizeof(gs);
}