On 06/05/2014 10:35 AM, Steven Rostedt wrote:
On Thu, 05 Jun 2014 10:12:16 -0700
David Daney <ddaney.cavm@xxxxxxxxx> wrote:
On 06/05/2014 09:12 AM, Steven Rostedt wrote:
I'm going through some of the warnings that Fengguang Wu's test bot has
discovered, and one of them is from a MIPS allmodconfig build.
https://lists.01.org/pipermail/kbuild-all/2014-May/004751.html
kernel/trace/trace_benchmark.c: In function 'trace_do_benchmark':
kernel/trace/trace_benchmark.c:84:3: warning: comparison of distinct pointer types lacks a cast [enabled by default]
kernel/trace/trace_benchmark.c:85:3: warning: comparison of distinct pointer types lacks a cast [enabled by default]
kernel/trace/trace_benchmark.c:38:6: warning: unused variable 'seedsq' [-Wunused-variable]
vim +84 kernel/trace/trace_benchmark.c
78 if (bm_cnt > 1) {
79 /*
80 * Apply Welford's method to calculate standard deviation:
81 * s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2)
82 */
83 stddev = (u64)bm_cnt * bm_totalsq - bm_total * bm_total;
> 84 do_div(stddev, bm_cnt);
> 85 do_div(stddev, bm_cnt - 1);
86 } else
87 stddev = 0;
88
Is there something special with do_div in mips that I should be aware
of?
Yes. MIPS is using the implementation in asm-generic/div64.h, which
per the comments in that file has a useless pointer compare to find just
this type of issue.
You mean this comment?
/* The unnecessary pointer compare is there
* to check for type safety (n must be 64bit)
*/
Yes.
But stddev is s64. Ah, but the compare is:
(void)(((typeof((n)) *)0) == ((uint64_t *)0));
so it's complaining about a signed verses unsigned compare, not length.
I think I can ignore this warning then.
The pedant in me thinks that you should fix your code if using do_div()
on a signed object is undefined. But if you aren't planning on merging
the code, then it probably doesn't matter.
Thoughts?
I think I will have lunch now...
David Daney
