Le 30/06/2020 à 18:33, Segher Boessenkool a écrit :

On Tue, Jun 30, 2020 at 04:55:05PM +0200, Christophe Leroy wrote:

quoted

Le 30/06/2020 à 03:19, Michael Ellerman a écrit :

quoted

Michael Ellerman [off-list ref] writes:

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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.

quoted

Changing it to "m" make it build.

But that just means something else is wrong.

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+ 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