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

[Christophe Leroy]

On 06/30/2020 04:33 PM, Segher Boessenkool wrote:
> On Tue, Jun 30, 2020 at 04:55:05PM +0200, Christophe Leroy wrote:
> > Le 30/06/2020 Ã 03:19, Michael Ellerman a ÃcritÂ:
> > > Michael Ellerman <mpe@xxxxxxxxxxxxxx> writes:
> > > > 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:
> >
> > Looks like 4.9.4 doesn't accept "m<>" constraint either.
>
> The evidence contradicts this assertion.
>
> > Changing it to "m" make it build.
>
> But that just means something else is wrong.
>
> > > + 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]))
> > >         ^
>
> Can we see what that was after the macro jungle?  Like, the actual
> preprocessed code?

Sorry for previous misunderstanding

Here is the code:

#define __put_user_asm(x, addr, err, op)			\
	__asm__ __volatile__(					\
		"1:	" op "%U2%X2 %1,%2	# put_user\n"	\
		"2:\n"						\
		".section .fixup,\"ax\"\n"			\
		"3:	li %0,%3\n"				\
		"	b 2b\n"					\
		".previous\n"					\
		EX_TABLE(1b, 3b)				\
		: "=r" (err)					\
		: "r" (x), "m<>" (*addr), "i" (-EFAULT), "0" (err))

Christophe