Hi Matthias, 2017-05-02 10:23 GMT+09:00 Matthias Kaehlcke <mka@xxxxxxxxxxxx>: > Hi Masahiro, > > El Sun, Apr 30, 2017 at 10:59:52PM +0900 Masahiro Yamada ha dit: > >> 2017-04-22 6:39 GMT+09:00 Matthias Kaehlcke <mka@xxxxxxxxxxxx>: >> > clang generates plenty of these warnings in different parts of the code, >> > to an extent that the warnings are little more than noise. Disable the >> > 'address-of-packed-member' warning. >> > >> > Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx> >> >> >> As far as I compiled arch/x86/configs/x86_64_defconfig, >> all address-of-packed-member warnings came from the single point: >> >> ./arch/x86/include/asm/processor.h:534:30: warning: taking address of >> packed member 'sp0' of class or structure 'x86_hw_tss' may result in >> an unaligned pointer value [-Waddress-of-packed-member] >> return this_cpu_read_stable(cpu_tss.x86_tss.sp0); >> ^~~~~~~~~~~~~~~~~~~ >> ./arch/x86/include/asm/percpu.h:391:59: note: expanded from macro >> 'this_cpu_read_stable' >> #define this_cpu_read_stable(var) percpu_stable_op("mov", var) >> ^~~ >> ./arch/x86/include/asm/percpu.h:228:16: note: expanded from macro >> 'percpu_stable_op' >> : "p" (&(var))); \ >> ^~~ >> >> >> >> For this case, I was able to fix it with the following patch: >> >> >> diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h >> index 9fa0360..de25d1c 100644 >> --- a/arch/x86/include/asm/percpu.h >> +++ b/arch/x86/include/asm/percpu.h >> @@ -211,26 +211,27 @@ do { >> \ >> #define percpu_stable_op(op, var) \ >> ({ \ >> typeof(var) pfo_ret__; \ >> + void *__p = &(var); \ >> switch (sizeof(var)) { \ >> case 1: \ >> asm(op "b "__percpu_arg(P1)",%0" \ >> : "=q" (pfo_ret__) \ >> - : "p" (&(var))); \ >> + : "p" (__p)); \ >> break; \ >> case 2: \ >> asm(op "w "__percpu_arg(P1)",%0" \ >> : "=r" (pfo_ret__) \ >> - : "p" (&(var))); \ >> + : "p" (__p)); \ >> break; \ >> case 4: \ >> asm(op "l "__percpu_arg(P1)",%0" \ >> : "=r" (pfo_ret__) \ >> - : "p" (&(var))); \ >> + : "p" (__p)); \ >> break; \ >> case 8: \ >> asm(op "q "__percpu_arg(P1)",%0" \ >> : "=r" (pfo_ret__) \ >> - : "p" (&(var))); \ >> + : "p" (__p)); \ >> break; \ >> default: __bad_percpu_size(); \ >> } \ > > Thanks for having a look! > > It is odd though that you only see warnings from that origin, I > encounter plenty of others with x86_64_defconfig, mostly stemming > from uaccess macros: > > kernel/power/user.c:439:35: warning: taking address of packed member > 'dev' of class or structure 'compat_resume_swap_area' may result in an > unaligned pointer value [-Waddress-of-packed-member] > err |= get_user(swap_area.dev, &u_swap_area->dev); > ^~~~~~~~~~~~~~~~ > ./arch/x86/include/asm/uaccess.h:168:23: note: expanded from macro 'get_user' > register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \ > ^~~ > ./arch/x86/include/asm/uaccess.h:132:41: note: expanded from macro '__inttype' > __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL)) > ^ > > I looked into fixing different cases, but didn't see a clear path > forward since we can't just cast the type away as in your patch above. Curious. I tested clang 3.0 thru 4.0, but I could not reproduce this. This part just calculates sizeof(*(ptr)). I think it is a false positive warning bug if clang reports this. -- Best Regards Masahiro Yamada -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html