On Fri, 06 Apr 2018 12:08:43 -0700
Joe Perches <joe@xxxxxxxxxxx> 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.
--
blue skies,
Martin.
"Reality continues to ruin my life." - Calvin.
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