Re: [PATCH v5 1/4] xen: introduce CONFIG_GENERIC_BUG_FRAME

[Jan Beulich <jbeulich@xxxxxxxx>]

On 03.03.2023 11:38, Oleksii Kurochko wrote:
> +int do_bug_frame(struct cpu_user_regs *regs, unsigned long pc)
> +{
> +    const struct bug_frame *bug = NULL;
> +    const struct virtual_region *region;
> +    const char *prefix = "", *filename, *predicate;
> +    unsigned long fixup;
> +    unsigned int id = BUGFRAME_NR, lineno;
> +
> +    region = find_text_region(pc);
> +    if ( !region )
> +        return -EINVAL;
> +
> +    for ( id = 0; id < BUGFRAME_NR; id++ )
> +    {
> +        const struct bug_frame *b;
> +        size_t i;
> +
> +        for ( i = 0, b = region->frame[id].bugs;
> +                i < region->frame[id].n_bugs; b++, i++ )
> +        {
> +            if ( bug_loc(b) == pc )
> +            {
> +                bug = b;
> +                goto found;
> +            }
> +        }
> +    }
> +
> + found:
> +    if ( !bug )
> +        return -EINVAL;
> +
> +    if ( id == BUGFRAME_run_fn )
> +    {
> +        void (*fn)(const struct cpu_user_regs *) = bug_ptr(bug);
> +
> +        fn(regs);
> +
> +        return id;
> +    }
> +
> +    /* WARN, BUG or ASSERT: decode the filename pointer and line number. */
> +    filename = bug_ptr(bug);
> +    if ( !is_kernel(filename) && !is_patch(filename) )
> +        return -EINVAL;
> +    fixup = strlen(filename);
> +    if ( fixup > 50 )
> +    {
> +        filename += fixup - 47;
> +        prefix = "...";
> +    }
> +    lineno = bug_line(bug);
> +
> +    switch ( id )
> +    {
> +    case BUGFRAME_warn:
> +        printk("Xen WARN at %s%s:%d\n", prefix, filename, lineno);
> +        show_execution_state(regs);
> +
> +        return id;
> +
> +    case BUGFRAME_bug:
> +        printk("Xen BUG at %s%s:%d\n", prefix, filename, lineno);
> +
> +        if ( BUG_DEBUGGER_TRAP_FATAL(regs) )
> +            return id;
> +
> +        show_execution_state(regs);
> +        panic("Xen BUG at %s%s:%d\n", prefix, filename, lineno);
> +
> +    case BUGFRAME_assert:
> +        /* ASSERT: decode the predicate string pointer. */
> +        predicate = bug_msg(bug);
> +        if ( !is_kernel(predicate) && !is_patch(predicate) )
> +            predicate = "<unknown>";
> +
> +        printk("Assertion '%s' failed at %s%s:%d\n",
> +               predicate, prefix, filename, lineno);
> +
> +        if ( BUG_DEBUGGER_TRAP_FATAL(regs) )
> +            return id;
> +
> +        show_execution_state(regs);
> +        panic("Assertion '%s' failed at %s%s:%d\n",
> +              predicate, prefix, filename, lineno);
> +    }
> +
> +    return id;
> +}

This final "return" looks like almost dead code (it isn't when an
unrecognized id is found). May I suggest to switch all "return id"
inside the switch() block to just "break", to make this final
"return" be (a) the central one and (b) more obviously a used path?

Jan