Re: [PATCH v7 1/5] xen: introduce CONFIG_GENERIC_BUG_FRAME

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.03.2023 14:33, Oleksii Kurochko wrote:
> --- /dev/null
> +++ b/xen/common/bug.c
> @@ -0,0 +1,107 @@
> +#include <xen/bug.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>
> +
> +/*
> + * 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 = BUGFRAME_NR, lineno;

Unnecessary initializer; "id" is set ...

> +    region = find_text_region(pc);
> +    if ( !region )
> +        return -EINVAL;
> +
> +    for ( id = 0; id < BUGFRAME_NR; id++ )

... unconditionally here.

> --- /dev/null
> +++ b/xen/include/xen/bug.h
> @@ -0,0 +1,162 @@
> +#ifndef __XEN_BUG_H__
> +#define __XEN_BUG_H__
> +
> +#define BUGFRAME_run_fn 0
> +#define BUGFRAME_warn   1
> +#define BUGFRAME_bug    2
> +#define BUGFRAME_assert 3
> +
> +#define BUGFRAME_NR     4
> +
> +#define BUG_DISP_WIDTH    24
> +#define BUG_LINE_LO_WIDTH (31 - BUG_DISP_WIDTH)
> +#define BUG_LINE_HI_WIDTH (31 - BUG_DISP_WIDTH)
> +
> +#include <asm/bug.h>
> +
> +#ifndef __ASSEMBLY__
> +
> +#ifndef BUG_DEBUGGER_TRAP_FATAL
> +#define BUG_DEBUGGER_TRAP_FATAL(regs) 0
> +#endif
> +
> +#include <xen/lib.h>
> +
> +#ifndef BUG_FRAME_STRUCT
> +
> +struct bug_frame {
> +    signed int loc_disp:BUG_DISP_WIDTH;
> +    unsigned int line_hi:BUG_LINE_HI_WIDTH;
> +    signed int ptr_disp:BUG_DISP_WIDTH;
> +    unsigned int line_lo:BUG_LINE_LO_WIDTH;
> +    signed int msg_disp[];
> +};
> +
> +#define bug_loc(b) ((unsigned long)(b) + (b)->loc_disp)
> +
> +#define bug_ptr(b) ((const void *)(b) + (b)->ptr_disp)
> +
> +#define bug_line(b) (((((b)->line_hi + ((b)->loc_disp < 0)) &                
> \
> +                       ((1 << BUG_LINE_HI_WIDTH) - 1)) <<                    
> \
> +                      BUG_LINE_LO_WIDTH) +                                   
> \
> +                     (((b)->line_lo + ((b)->ptr_disp < 0)) &                 
> \
> +                      ((1 << BUG_LINE_LO_WIDTH) - 1)))
> +
> +#define bug_msg(b) ((const char *)(b) + (b)->msg_disp[1])
> +
> +#ifndef BUILD_BUG_ON_LINE_WIDTH
> +#define BUILD_BUG_ON_LINE_WIDTH(line) \
> +    BUILD_BUG_ON((line) >> (BUG_LINE_LO_WIDTH + BUG_LINE_HI_WIDTH))
> +#endif

I still don't see why you have #ifdef here. What I would expect is (as
expressed before)

#define BUILD_BUG_ON_LINE_WIDTH(line) \
    BUILD_BUG_ON((line) >> (BUG_LINE_LO_WIDTH + BUG_LINE_HI_WIDTH))

#else  /* BUG_FRAME_STRUCT */

#ifndef BUILD_BUG_ON_LINE_WIDTH
#define BUILD_BUG_ON_LINE_WIDTH(line) ((void)(line)
#endif

(perhaps shortened to

#elif !defined(BUILD_BUG_ON_LINE_WIDTH)
#define BUILD_BUG_ON_LINE_WIDTH(line) ((void)(line)

)

> +#endif /* BUG_FRAME_STRUCT */

... and then the separate conditional further down dropped. Have you
found anything speaking against this approach?

Jan