On Sun, 22 Nov 2015, Arnd Bergmann wrote: > On Monday 16 November 2015 20:20:38 you wrote: > > Arnd, > > > > Please pull the following branch: > > > > git://git.linaro.org/people/nicolas.pitre/linux div64 > > > > This contains those patches I've initially posted here: > > > > https://lkml.org/lkml/2015/11/2/715 > > > > Only changes to those posted patches are cosmetic improvements such as > > the use of ilog2() replacing the custom __div64_ffs(). Exposure in > > linux-next would be a good thing. > > > > I also included fixes for a couple do_div() misuses that an allyesconfig > > build turned up after switching ARM to the generic do_div() code. > > Those patches have been posted separately and addressed to relevant > > maintainers. They are included here until/unless those maintainers > > include those patches in their tree. > > > > Original cover letter: > > > > This is a generalization of the optimization I produced for ARM a decade > > ago to turn constant divisors into a multiplication by the divisor > > reciprocal. Turns out that after all those years gcc is still not > > optimizing things on its own for that case. > > > > This has important performance benefits as discussed in this thread: > > > > https://lkml.org/lkml/2015/10/28/851 > > > > This series brings the formerly ARM-only optimization to all 32-bit > > architectures using C code by default. The possibility for the actual > > multiplication to be implemented in assembly is provided in order to get > > optimal code. The ARM version can be used as an example implementation > > for other interested architectures to implement. > > 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' This looks like some gcc bug from a few years ago. > I've verified that this goes away if I turn off CONFIG_PROFILE_ALL_BRANCHES, > and it only shows up with gcc-5.0 through gcc-5.2.1, but not 4.9.3. > > Aside from those, I have not been able to reduce the failure scenario. > > Also, I have only tested on ARM32, no idea if this shows up elsewhere. What if you revert "ARM: asm/div64.h: adjust to generic codde" and recompile? Nicolas -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
