Messages in this thread | | | Subject | Re: [PATCH v2] err.h: allow IS_ERR_VALUE to handle properly more types | From | Andrzej Hajda <> | Date | Wed, 03 Feb 2016 11:53:02 +0100 |
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On 02/03/2016 01:33 AM, Andrew Morton wrote: > On Thu, 28 Jan 2016 09:27:28 +0100 Andrzej Hajda <a.hajda@samsung.com> wrote: > >> - use '<= 0' instead of '< 0' to silence gcc verbose warnings, >> - expand commit message. >> --- >> include/linux/err.h | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/include/linux/err.h b/include/linux/err.h >> index 56762ab..43a6adb 100644 >> --- a/include/linux/err.h >> +++ b/include/linux/err.h >> @@ -18,7 +18,9 @@ >> >> #ifndef __ASSEMBLY__ >> >> -#define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO) >> +#define IS_ERR_VALUE(x) ((typeof(x))(-1) <= 0 \ >> + ? unlikely((x) < 0) \ >> + : unlikely((x) >= (typeof(x))-MAX_ERRNO)) > I'm still getting a bunch of > > include/linux/err.h: In function 'IS_ERR': > include/linux/err.h:37: warning: comparison of unsigned expression < 0 is always false > include/linux/err.h: In function 'IS_ERR_OR_NULL': > include/linux/err.h:42: warning: comparison of unsigned expression < 0 is always false > > with gcc-4.4.4. > >
These warnings are false positives and gcc up to 4.7 emits them, gcc 4.8(which I use) behaves correctly (at least on x86 and arm64). I have tried to use __builtin_choose_expr instead of ?: operator but it did not help, although documentation says "the built-in function does not evaluate the expression that is not chosen"[1].
The sanest gcc silencer I see for now is to replace: ? unlikely((x) < 0) \ with ? unlikely((x) <= -1) \
On the other side these warnings are caused by -Wtype-limits switch which is disabled by default in kernel build and treated as broken by Linus [2]. Maybe it is good enough reason to disregard them? :)
Anyway, I will post another iteration.
[1]: https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#index-g_t_005f_005fbuiltin_005fchoose_005fexpr-4184 [2]: http://permalink.gmane.org/gmane.linux.kernel/2053963
Regards Andrzej
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