Subject: Re: [PATCH v2] powerpc/uaccess: Use flexible addressing with __put_user()/__get_user()

From: Michael Ellerman <[email-masked]>
Date: Tue, 30 Jun 2020 11:19:29 +1000

Michael Ellerman <[email-masked]> writes:
> Christophe Leroy <[email-masked]> writes:
>> Hi Michael,
>>
>> I see this patch is marked as "defered" in patchwork, but I can't see 
>> any related discussion. Is it normal ?
>
> Because it uses the "m<>" constraint which didn't work on GCC 4.6.
>
> https://github.com/linuxppc/issues/issues/297
>
> So we should be able to pick it up for v5.9 hopefully.

It seems to break the build with the kernel.org 4.9.4 compiler and
corenet64_smp_defconfig:

+ make -s CC=powerpc64-linux-gnu-gcc -j 160
In file included from /linux/include/linux/uaccess.h:11:0,
                 from /linux/include/linux/sched/task.h:11,
                 from /linux/include/linux/sched/signal.h:9,
                 from /linux/include/linux/rcuwait.h:6,
                 from /linux/include/linux/percpu-rwsem.h:7,
                 from /linux/include/linux/fs.h:33,
                 from /linux/include/linux/huge_mm.h:8,
                 from /linux/include/linux/mm.h:675,
                 from /linux/arch/powerpc/kernel/signal_32.c:17:
/linux/arch/powerpc/kernel/signal_32.c: In function 'save_user_regs.isra.14.constprop':
/linux/arch/powerpc/include/asm/uaccess.h:161:2: error: 'asm' operand has impossible constraints
  __asm__ __volatile__(     \
  ^
/linux/arch/powerpc/include/asm/uaccess.h:197:12: note: in expansion of macro '__put_user_asm'
    case 4: __put_user_asm(x, ptr, retval, "stw"); break; \
            ^
/linux/arch/powerpc/include/asm/uaccess.h:206:2: note: in expansion of macro '__put_user_size_allowed'
  __put_user_size_allowed(x, ptr, size, retval);  \
  ^
/linux/arch/powerpc/include/asm/uaccess.h:220:2: note: in expansion of macro '__put_user_size'
  __put_user_size(__pu_val, __pu_addr, __pu_size, __pu_err); \
  ^
/linux/arch/powerpc/include/asm/uaccess.h:96:2: note: in expansion of macro '__put_user_nocheck'
  __put_user_nocheck((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr)))
  ^
/linux/arch/powerpc/kernel/signal_32.c:120:7: note: in expansion of macro '__put_user'
   if (__put_user((unsigned int)gregs[i], &frame->mc_gregs[i]))
       ^
/linux/scripts/Makefile.build:280: recipe for target 'arch/powerpc/kernel/signal_32.o' failed
make[3]: *** [arch/powerpc/kernel/signal_32.o] Error 1
make[3]: *** Waiting for unfinished jobs....
In file included from /linux/include/linux/uaccess.h:11:0,
                 from /linux/include/linux/sched/task.h:11,
                 from /linux/include/linux/sched/signal.h:9,
                 from /linux/include/linux/rcuwait.h:6,
                 from /linux/include/linux/percpu-rwsem.h:7,
                 from /linux/include/linux/fs.h:33,
                 from /linux/include/linux/huge_mm.h:8,
                 from /linux/include/linux/mm.h:675,
                 from /linux/arch/powerpc/kernel/signal_64.c:12:
/linux/arch/powerpc/kernel/signal_64.c: In function '__se_sys_swapcontext':
/linux/arch/powerpc/include/asm/uaccess.h:319:2: error: 'asm' operand has impossible constraints
  __asm__ __volatile__(    \
  ^
/linux/arch/powerpc/include/asm/uaccess.h:359:10: note: in expansion of macro '__get_user_asm'
  case 1: __get_user_asm(x, (u8 __user *)ptr, retval, "lbz"); break; \
          ^
/linux/arch/powerpc/include/asm/uaccess.h:370:2: note: in expansion of macro '__get_user_size_allowed'
  __get_user_size_allowed(x, ptr, size, retval);  \
  ^
/linux/arch/powerpc/include/asm/uaccess.h:393:3: note: in expansion of macro '__get_user_size'
   __get_user_size(__gu_val, __gu_addr, __gu_size, __gu_err); \
   ^
/linux/arch/powerpc/include/asm/uaccess.h:94:2: note: in expansion of macro '__get_user_nocheck'
  __get_user_nocheck((x), (ptr), sizeof(*(ptr)), true)
  ^
/linux/arch/powerpc/kernel/signal_64.c:672:9: note: in expansion of macro '__get_user'
      || __get_user(tmp, (u8 __user *) new_ctx + ctx_size - 1))
         ^
/linux/scripts/Makefile.build:280: recipe for target 'arch/powerpc/kernel/signal_64.o' failed
make[3]: *** [arch/powerpc/kernel/signal_64.o] Error 1
/linux/scripts/Makefile.build:497: recipe for target 'arch/powerpc/kernel' failed
make[2]: *** [arch/powerpc/kernel] Error 2
/linux/Makefile:1756: recipe for target 'arch/powerpc' failed
make[1]: *** [arch/powerpc] Error 2
Makefile:185: recipe for target '__sub-make' failed
make: *** [__sub-make] Error 2

cheers