Messages in this thread | | | Subject | Re: [PATCH v2 8/9] lib/vsprintf: Remove useless NULL checks | From | Andy Shevchenko <> | Date | Tue, 27 Feb 2018 19:35:50 +0200 |
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On Tue, 2018-02-27 at 16:50 +0100, Petr Mladek wrote: > On Fri 2018-02-16 23:07:10, Andy Shevchenko wrote: > > The pointer can't be NULL since it's first what has been done in the > > pointer(). > > > > Remove useless checks. > > > > Note we leave check for !CONFIG_HAVE_CLK to make compiler > > to optimize code away when possible. > > > > Cc: Petr Mladek <pmladek@suse.com> > > Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> > > --- > > lib/vsprintf.c | 13 +------------ > > 1 file changed, 1 insertion(+), 12 deletions(-) > > > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > > index 97be2d07297a..a49da00b79e7 100644 > > --- a/lib/vsprintf.c > > +++ b/lib/vsprintf.c > > @@ -819,10 +819,6 @@ char *hex_string(char *buf, char *end, u8 > > *addr, struct printf_spec spec, > > /* nothing to print */ > > return buf; > > > > - if (ZERO_OR_NULL_PTR(addr)) > > This macro matches also values <= 16.
Yes, I know.
This had been discussed with Rasmus and we agreed that printing a result of kmalloc(0) is rather weird.
Moreover, in couple of cases I added these checks.
> > switch (fmt[1]) { > > @@ -1580,9 +1572,6 @@ char *device_node_string(char *buf, char *end, > > struct device_node *dn, > > if (!IS_ENABLED(CONFIG_OF)) > > return string(buf, end, "(!OF)", spec); > > > > - if ((unsigned long)dn < PAGE_SIZE) > > - return string(buf, end, "(null)", spec); > > In this case, "null" was printed for ptr < PAGE_SIZE. The same check > is also in string() function.
Do we have a uses cases when invalid (non-NULL) pointer is supplied to print function?
Those call sites have to be fixed.
> Note that it is not only about the printed value. The pointer is later > derefecend. We will start crashing on dn > 0 && dn < PAGE_SIZE.
Yes. So, fix the call sites!
> To be honest, I do not feel experienced enough to decide > about the preferred behavior. On one hand, it is bad when > printk() would crash the kernel. On the other hand, hiding wide > range of values under "(null)" string might confuse people.
> Would it make sense to survive and write different strings for > difference intervals? For example? > > "(null)" for ptr == 0 > "(null-16)" for ptr > 0 && ptr <= 16 > "(null-pg)" for prt > 16 && ptr <= PAGE_SIZE > > In each case, this patch changes the behavior and it should > be documented in the commit message.
Personally I strongly disagree with blowing code up in such places for little or none benefit.
-- Andy Shevchenko <andriy.shevchenko@linux.intel.com> Intel Finland Oy
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