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

[Christophe Leroy]

[Not sure you got it, resending with the file compressed]

Le 30/06/2020 à 18:33, Segher Boessenkool a écrit :
> On Tue, Jun 30, 2020 at 04:55:05PM +0200, Christophe Leroy wrote:
>> Le 30/06/2020 à 03:19, Michael Ellerman a écrit :
>>> Michael Ellerman <mpe at ellerman.id.au> 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?

Preprocessor output attached

>
> Also, what GCC version *does* work on this?

Among the versions available in kernel.org crosstool
4.7.3 is too old
4.8.5 has this error
4.9.4 has this error
5.5.0 works

With 4.9.4:
- it also fails with powerpc64e_defconfig
- it works with mpc885_ads_defconfig and with powerpc64_defconfig

Christophe


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