Re: [PATCH] vsyscall: use __iter_div_u64_rem()

[Vincenzo Frascino]

Hi Arnd,

On 11/07/2019 13:28, Arnd Bergmann wrote:
> On Thu, Jul 11, 2019 at 2:14 PM Vincenzo Frascino
> <vincenzo.frascino@xxxxxxx> wrote:
>>
>>
>> Could you please tell me which version of the compiler did you use?
>>
>> My building command is:
>>
>> # make mrproper && make CC=clang HOSTCC=clang i386_defconfig && make ARCH=i386
>> CC=clang HOSTCC=clang -j56
>>
> 
> See below for the patch I am using locally to work around this.
> That patch is probably wrong, so I have not submitted it yet, but it
> gives you a clean build ;-)
> 
>      Arnd
> 

Thank you, I will give it a go :-)

> 8<---
> Subject: [PATCH] x86: percpu: fix clang 32-bit build
> 
> clang does not like an inline assembly with a "=q" contraint for
> a 64-bit output:
> 
> arch/x86/events/perf_event.h:824:21: error: invalid output size for
> constraint '=q'
>         u64 disable_mask = __this_cpu_read(cpu_hw_events.perf_ctr_virt_mask);
>                            ^
> include/linux/percpu-defs.h:447:2: note: expanded from macro '__this_cpu_read'
>         raw_cpu_read(pcp);                                              \
>         ^
> include/linux/percpu-defs.h:421:28: note: expanded from macro 'raw_cpu_read'
>  #define raw_cpu_read(pcp)
> __pcpu_size_call_return(raw_cpu_read_, pcp)
>                                         ^
> include/linux/percpu-defs.h:322:23: note: expanded from macro
> '__pcpu_size_call_return'
>         case 1: pscr_ret__ = stem##1(variable); break;                  \
>                              ^
> <scratch space>:357:1: note: expanded from here
> raw_cpu_read_1
> ^
> arch/x86/include/asm/percpu.h:394:30: note: expanded from macro 'raw_cpu_read_1'
>  #define raw_cpu_read_1(pcp)             percpu_from_op(, "mov", pcp)
>                                         ^
> arch/x86/include/asm/percpu.h:189:15: note: expanded from macro 'percpu_from_op'
>                     : "=q" (pfo_ret__)                  \
>                             ^
> 
> According to the commit that introduced the "q" constraint, this was
> needed to fix miscompilation, but it gives no further detail.
> 
> Using the normal "=r" constraint seems to work so far.
> 
> Fixes: 3c598766a2ba ("x86: fix percpu_{to,from}_op()")
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> 
> diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
> index 2278797c769d..e791fbf4018f 100644
> --- a/arch/x86/include/asm/percpu.h
> +++ b/arch/x86/include/asm/percpu.h
> @@ -99,7 +99,7 @@ do {                                                  \
>         case 1:                                         \
>                 asm qual (op "b %1,"__percpu_arg(0)     \
>                     : "+m" (var)                        \
> -                   : "qi" ((pto_T__)(val)));           \
> +                   : "ri" ((pto_T__)(val)));           \
>                 break;                                  \
>         case 2:                                         \
>                 asm qual (op "w %1,"__percpu_arg(0)     \
> @@ -144,7 +144,7 @@ do {
>                          \
>                 else                                                    \
>                         asm qual ("addb %1, "__percpu_arg(0)            \
>                             : "+m" (var)                                \
> -                           : "qi" ((pao_T__)(val)));                   \
> +                           : "ri" ((pao_T__)(val)));                   \
>                 break;                                                  \
>         case 2:                                                         \
>                 if (pao_ID__ == 1)                                      \
> @@ -186,7 +186,7 @@ do {
>                          \
>         switch (sizeof(var)) {                          \
>         case 1:                                         \
>                 asm qual (op "b "__percpu_arg(1)",%0"   \
> -                   : "=q" (pfo_ret__)                  \
> +                   : "=r" (pfo_ret__)                  \
>                     : "m" (var));                       \
>                 break;                                  \
>         case 2:                                         \
> @@ -215,7 +215,7 @@ do {
>                          \
>         switch (sizeof(var)) {                          \
>         case 1:                                         \
>                 asm(op "b "__percpu_arg(P1)",%0"        \
> -                   : "=q" (pfo_ret__)                  \
> +                   : "=r" (pfo_ret__)                  \
>                     : "p" (&(var)));                    \
>                 break;                                  \
>         case 2:                                         \
> 

-- 
Regards,
Vincenzo