On Mon, 2018-04-09 at 14:39 +0200, Martin Schwidefsky wrote:
> On Fri, 06 Apr 2018 12:08:43 -0700
> Joe Perches <j...@perches.com> wrote:
>
> > debug_sprintf_event calls __debug_sprintf_event
> > with a format and arguments.
> >
> > There various types of arguments used in these
> > call, but __debug_sprintf_event uses va_arg
> > with only long as the type argument so random
> > errors could occur because the type and argument
> > are supposed to match.
> >
> > debug_entry_t *__debug_sprintf_event(debug_info_t *id, int level, char
> > *string, ...)
> > {
> > [...]
> > va_start(ap, string);
> > curr_event->string = string;
> > for (idx = 0; idx < min(numargs, (int)(id->buf_size /
> > sizeof(long)) - 1); idx++)
> > curr_event->args[idx] = va_arg(ap, long);
> > va_end(ap);
> > [...]
> > }
> >
> > from man va_arg
> >
> > va_arg()
> >
> > if type is not compatible with the type of the actual next argument
> > (as promoted according to the default argument promotions),
> > random errors will occur.
> >
> > For instance, uses like:
> >
> > arch/s390/kernel/perf_cpum_sf.c:919: debug_sprintf_event(sfdbg, 6,
> > "pmu_enable: es=%i cs=%i ed=%i cd=%i "
> > arch/s390/kernel/perf_cpum_sf.c-920- "tear=%p
> > dear=%p\n", cpuhw->lsctl.es, cpuhw->lsctl.cs,
> > arch/s390/kernel/perf_cpum_sf.c-921-
> > cpuhw->lsctl.ed, cpuhw->lsctl.cd,
> > arch/s390/kernel/perf_cpum_sf.c-922- (void *)
> > cpuhw->lsctl.tear, (void *) cpuhw->lsctl.dear);
> >
> > where the first 3 arguments are int but their type
> > as used by va_arg in __debug_sprintf_event is long
> > which could produce random errors.
>
> In principle you are right that the va_arg handling is not 100%
> correct. It works though because the C ABI for s390x requires
> that arguments are sign- or zero-extended to 64 bits by the caller
> of a function. This is true for values passed in registers and for
> the variable argument list.
Thanks.
Reference:
http://legacy.redhat.com/pub/redhat/linux/7.1/es/os/s390x/doc/lzsabi0.pdf
(found via your explanation)
It might be nice to explain that somewhere in
Documentation/s390 if it's not there already.
