Re: [PATCH v8 1/5] xen: introduce CONFIG_GENERIC_BUG_FRAME

[Jan Beulich <jbeulich@xxxxxxxx>]

On 17.03.2023 10:23, Oleksii wrote:
> On Thu, 2023-03-16 at 12:26 +0100, Jan Beulich wrote:
>> On 15.03.2023 18:21, Oleksii Kurochko wrote:
>>> --- /dev/null
>>> +++ b/xen/common/bug.c
>>> @@ -0,0 +1,108 @@
>>> +#include <xen/bug.h>
>>> +#include <xen/debugger.h>
>>> +#include <xen/errno.h>
>>> +#include <xen/kernel.h>
>>> +#include <xen/livepatch.h>
>>> +#include <xen/string.h>
>>> +#include <xen/types.h>
>>> +#include <xen/virtual_region.h>
>>> +
>>> +#include <asm/processor.h>
>>
>> I actually meant to also ask: What is this needed for? Glancing over
>> the
>> code ...
>>
>>> +/*
>>> + * Returns a negative value in case of an error otherwise
>>> + * BUGFRAME_{run_fn, warn, bug, assert}
>>> + */
>>> +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, 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 -ENOENT;
>>> +
>>> +    if ( id == BUGFRAME_run_fn )
>>> +    {
>>> +        void (*fn)(struct cpu_user_regs *) = bug_ptr(bug);
>>> +
>>> +        fn(regs);
>>> +
>>> +        /* Re-enforce consistent types, because of the casts
>>> involved. */
>>> +        if ( false )
>>> +            run_in_exception_handler(fn);
>>> +
>>> +        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);
>>> +
>>> +        break;
>>> +
>>> +    case BUGFRAME_bug:
>>> +        printk("Xen BUG at %s%s:%d\n", prefix, filename, lineno);
>>> +
>>> +        if ( BUG_DEBUGGER_TRAP_FATAL(regs) )
>>> +            break;
>>> +
>>> +        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) )
>>> +            break;
>>> +
>>> +        show_execution_state(regs);
>>> +        panic("Assertion '%s' failed at %s%s:%d\n",
>>> +              predicate, prefix, filename, lineno);
>>> +    }
>>> +
>>> +    return id;
>>> +}
>>
>> ... I can't really spot what it might be that comes from that header.
>> Oh, on the N+1st run I've spotted it - it's show_execution_state().
>> The declaration of which, already being used from common code ahead
>> of this series, should imo be moved to a common header. I guess I'll
>> make yet another patch ...
> As mentioned above. Not only show_execution_state() but also
> cpu_user_regs structure. ( at lest, for ARM & RISCV )

Do we deref "regs" anywhere? I can't seem to be able to spot an instance.
Without a deref (or alike) a forward decl is all that's needed for this
code to compile.

Jan