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

[Oleksii <oleksii.kurochko@xxxxxxxxx>]

On Fri, 2023-03-17 at 15:59 +0100, Jan Beulich wrote:
> 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.
You are there is no a deref so let's swich to a forward decl.

I'll add it to a new version of the patch series.

~ Oleksii