Messages in this thread Patch in this message | | | Date | Mon, 23 Nov 2015 11:04:33 -0500 (EST) | From | Nicolas Pitre <> | Subject | Re: [GIT PULL] optimize 64-by-32 ddivision for constant divisors on 32-bit machines |
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On Mon, 23 Nov 2015, Nicolas Pitre wrote:
> On Mon, 23 Nov 2015, Arnd Bergmann wrote: > > > On Sunday 22 November 2015 17:28:33 Nicolas Pitre wrote: > > > On Sun, 22 Nov 2015, Arnd Bergmann wrote: > > > > On Monday 16 November 2015 20:20:38 you wrote: > > > > I'm now getting a build regressing with the attached randconfig configuration, > > > > when compiling drivers/net/wireless/iwlegacy/common.o: > > > > > > > > drivers/built-in.o: In function `il_send_rxon_timing': > > > > :(.text+0xbbac80): undefined reference to `__aeabi_uldivmod' > > > > :(.text+0xbbac9c): undefined reference to `__aeabi_uldivmod' > > > > :(.text+0xbbacdc): undefined reference to `__aeabi_uldivmod' > > > > :(.text+0xbbadc8): undefined reference to `__aeabi_uldivmod' > > > > :(.text+0xbbadf8): undefined reference to `__aeabi_uldivmod' > > > > :(.text+0xbbae3c): more undefined references to `__aeabi_uldivmod' follow > > > > drivers/built-in.o: In function `il_send_rxon_timing': > > > > :(.text+0xbbb11c): undefined reference to `____ilog2_NaN' > > > > > I'm able to reproduce it, and I am in the process of reintroducing the > last patch piece by piece to see what breaks. The presence of > ____ilog2_NaN is particularly intriguing as this would mean 0 is passed > to ilog2() somewhere.
OK... I'm able to "fix" the build with:
diff --git a/include/asm-generic/div64.h b/include/asm-generic/div64.h index 163f77999e..d246c4c801 100644 --- a/include/asm-generic/div64.h +++ b/include/asm-generic/div64.h @@ -206,7 +206,7 @@ extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor); uint32_t __rem; \ (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \ if (__builtin_constant_p(__base) && \ - is_power_of_2(__base)) { \ + is_power_of_2(__base) && __base != 0) { \ __rem = (n) & (__base - 1); \ (n) >>= ilog2(__base); \ } else if (__div64_const32_is_OK && \ What doesn't make sense to me is the fact that is_power_of_2() is defined as:
static inline __attribute__((const)) bool is_power_of_2(unsigned long n) { return (n != 0 && ((n & (n - 1)) == 0)); } So the test for zero is already in there.
And adding BUILD_BUG_ON(__builtin_constant_p(__base) && __base == 0) before the if doesn't trig either.
Confused.
Nicolas
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