Re: [PATCH] vsyscall: use __iter_div_u64_rem()

[Arnd Bergmann]

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

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:                                         \