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SubjectRe: [PATCH v2] powerpc/uaccess: Use flexible addressing with __put_user()/__get_user()
Hi again,

Thanks for your work so far!

On Tue, Jun 30, 2020 at 06:53:39PM +0000, Christophe Leroy wrote:
> On 06/30/2020 04:33 PM, Segher Boessenkool wrote:
> >>>+ 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))

Yeah I don't see it. I'll have to look at compiler debug dumps, but I
don't have any working 4.9 around, and I cannot reproduce this with
either older or newer compilers.

It is complainig that constrain_operands just does not work *at all* on
this "m<>" constraint apparently, which doesn't make much sense.

I'll try later when I have more time, sorry :-/


Segher

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