Re: [PATCH v3 1/4] xen: introduce CONFIG_GENERIC_BUG_FRAME

[Oleksii <oleksii.kurochko@gmail.com>]

On Mon, 2023-02-27 at 15:23 +0100, Jan Beulich wrote:
> On 24.02.2023 12:31, Oleksii Kurochko wrote:
> > --- /dev/null
> > +++ b/xen/common/bug.c
> > @@ -0,0 +1,109 @@
> > +#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>
> > +
> > +/* Set default value for TRAP_invalid_op as it is defined only for
> > X86 now */
> > +#ifndef TRAP_invalid_op
> > +#define TRAP_invalid_op 0
> > +#endif
> > +
> > +int do_bug_frame(const 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 )
> > +    {
> > +        for ( id = 0; id < BUGFRAME_NR; id++ )
> > +        {
> > +            const struct bug_frame *b;
> > +            unsigned int 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 )
> > +    {
> > +#ifdef BUG_FN_REG
> > +        void (*fn)(const struct cpu_user_regs *) = (void *)regs-
> > >BUG_FN_REG;
> > +#else
> > +        void (*fn)(const struct cpu_user_regs *) = bug_ptr(bug);
> > +#endif
> > +
> > +        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 ( debugger_trap_fatal(TRAP_invalid_op, regs) )
> 
> TRAP_invalid_op is, as said, about to disappear on x86 as well. I
> think
> this construct wants abstracting by another asm/bug.h provided macro
> (taking just regs).
> 
Thanks for the link.

Nice idea to abstract 'debugger_trap_fatal(TRAP_invalid_op, regs)'.
Actually we have to options here:
1. As you proposed abstract in <asm/bug.h>:
   x86:  #define DEBUG_TRAP_FATAL(regs) debugger_trap_fatal(X86_EXC_GP,
regs)
   ARM: #define DEBUG_TRAP_FATAL(regs) 0
   RISC-V: #define DEBUG_TRAP_FATAL(regs) 0
  For ARM and RISC-V it doesn't use so we can skip the check if (
DEBUG_TRAP_FATAL ).

2. Abstract only TRAP_invalid_op in <asm/bug.h>
  x86: #define TRAP_invalud_op X86_EXC_GP
  RISC-V: #define TRAP_invalid_op 0
  ARN: #define TRAP_invalid_op 0
  
  I am not sure if we have to provide real invalid opcodes for RISC-V
and ARM as it looks like debug_trap_fatal() isn't used in ARM&RISC-V
now.

Could you please suggest which one option is better?

~ Oleksii

  

> Jan