* [PATCH] vsyscall: use __iter_div_u64_rem() @ 2019-07-10 13:01 Arnd Bergmann 2019-07-10 16:56 ` Nathan Chancellor 2019-07-11 12:14 ` Vincenzo Frascino 0 siblings, 2 replies; 7+ messages in thread From: Arnd Bergmann @ 2019-07-10 13:01 UTC (permalink / raw) To: Andy Lutomirski, Thomas Gleixner, Vincenzo Frascino Cc: linux-arch, Shuah Khan, linux-kernel, Arnd Bergmann, Huw Davies, Catalin Marinas, Daniel Lezcano, Will Deacon, linux-mips, Ralf Baechle, Russell King, clang-built-linux, Paul Burton, linux-kselftest, Rasmus Villemoes, Dmitry Safonov, Mark Salyzyn, Peter Collingbourne, linux-arm-kernel On 32-bit x86 when building with clang-9, the loop gets turned back into an inefficient division that causes a link error: kernel/time/vsyscall.o: In function `update_vsyscall': vsyscall.c:(.text+0xe3): undefined reference to `__udivdi3' Use the provided __iter_div_u64_rem() function that is meant to address the same case in other files. Fixes: 44f57d788e7d ("timekeeping: Provide a generic update_vsyscall() implementation") Signed-off-by: Arnd Bergmann <arnd@arndb.de> --- kernel/time/vsyscall.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/kernel/time/vsyscall.c b/kernel/time/vsyscall.c index a80893180826..8cf3596a4ce6 100644 --- a/kernel/time/vsyscall.c +++ b/kernel/time/vsyscall.c @@ -104,11 +104,7 @@ void update_vsyscall(struct timekeeper *tk) vdso_ts->sec = tk->xtime_sec + tk->wall_to_monotonic.tv_sec; nsec = tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift; nsec = nsec + tk->wall_to_monotonic.tv_nsec; - while (nsec >= NSEC_PER_SEC) { - nsec = nsec - NSEC_PER_SEC; - vdso_ts->sec++; - } - vdso_ts->nsec = nsec; + vdso_ts->sec += __iter_div_u64_rem(nsec, NSEC_PER_SEC, &vdso_ts->nsec); if (__arch_use_vsyscall(vdata)) update_vdso_data(vdata, tk); -- 2.20.0 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] vsyscall: use __iter_div_u64_rem() 2019-07-10 13:01 [PATCH] vsyscall: use __iter_div_u64_rem() Arnd Bergmann @ 2019-07-10 16:56 ` Nathan Chancellor 2019-07-11 12:14 ` Vincenzo Frascino 1 sibling, 0 replies; 7+ messages in thread From: Nathan Chancellor @ 2019-07-10 16:56 UTC (permalink / raw) To: Arnd Bergmann Cc: linux-arch, Shuah Khan, linux-kernel, linux-kselftest, Dmitry Safonov, Mark Salyzyn, Huw Davies, Catalin Marinas, Daniel Lezcano, Will Deacon, linux-mips, Ralf Baechle, Russell King, clang-built-linux, Paul Burton, Andy Lutomirski, Rasmus Villemoes, Thomas Gleixner, Vincenzo Frascino, Peter Collingbourne, linux-arm-kernel On Wed, Jul 10, 2019 at 03:01:53PM +0200, Arnd Bergmann wrote: > On 32-bit x86 when building with clang-9, the loop gets turned back into > an inefficient division that causes a link error: > > kernel/time/vsyscall.o: In function `update_vsyscall': > vsyscall.c:(.text+0xe3): undefined reference to `__udivdi3' > > Use the provided __iter_div_u64_rem() function that is meant to address > the same case in other files. > > Fixes: 44f57d788e7d ("timekeeping: Provide a generic update_vsyscall() implementation") > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > --- > kernel/time/vsyscall.c | 6 +----- > 1 file changed, 1 insertion(+), 5 deletions(-) > > diff --git a/kernel/time/vsyscall.c b/kernel/time/vsyscall.c > index a80893180826..8cf3596a4ce6 100644 > --- a/kernel/time/vsyscall.c > +++ b/kernel/time/vsyscall.c > @@ -104,11 +104,7 @@ void update_vsyscall(struct timekeeper *tk) > vdso_ts->sec = tk->xtime_sec + tk->wall_to_monotonic.tv_sec; > nsec = tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift; > nsec = nsec + tk->wall_to_monotonic.tv_nsec; > - while (nsec >= NSEC_PER_SEC) { > - nsec = nsec - NSEC_PER_SEC; > - vdso_ts->sec++; > - } > - vdso_ts->nsec = nsec; > + vdso_ts->sec += __iter_div_u64_rem(nsec, NSEC_PER_SEC, &vdso_ts->nsec); > > if (__arch_use_vsyscall(vdata)) > update_vdso_data(vdata, tk); > -- > 2.20.0 > What an interesting function. Looks good to me and I can confirm it fixes the link error. Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> Tested-by: Nathan Chancellor <natechancellor@gmail.com> _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] vsyscall: use __iter_div_u64_rem() 2019-07-10 13:01 [PATCH] vsyscall: use __iter_div_u64_rem() Arnd Bergmann 2019-07-10 16:56 ` Nathan Chancellor @ 2019-07-11 12:14 ` Vincenzo Frascino 2019-07-11 12:28 ` Arnd Bergmann 1 sibling, 1 reply; 7+ messages in thread From: Vincenzo Frascino @ 2019-07-11 12:14 UTC (permalink / raw) To: Arnd Bergmann, Andy Lutomirski, Thomas Gleixner Cc: linux-arch, Shuah Khan, linux-kernel, Dmitry Safonov, Huw Davies, Catalin Marinas, Daniel Lezcano, Will Deacon, linux-mips, Ralf Baechle, Russell King, clang-built-linux, Paul Burton, linux-kselftest, Rasmus Villemoes, Mark Salyzyn, Peter Collingbourne, linux-arm-kernel Hi Arnd, On 10/07/2019 14:01, Arnd Bergmann wrote: > On 32-bit x86 when building with clang-9, the loop gets turned back into > an inefficient division that causes a link error: > > kernel/time/vsyscall.o: In function `update_vsyscall': > vsyscall.c:(.text+0xe3): undefined reference to `__udivdi3' > > Use the provided __iter_div_u64_rem() function that is meant to address > the same case in other files. > > Fixes: 44f57d788e7d ("timekeeping: Provide a generic update_vsyscall() implementation") > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > --- > kernel/time/vsyscall.c | 6 +----- > 1 file changed, 1 insertion(+), 5 deletions(-) > > diff --git a/kernel/time/vsyscall.c b/kernel/time/vsyscall.c > index a80893180826..8cf3596a4ce6 100644 > --- a/kernel/time/vsyscall.c > +++ b/kernel/time/vsyscall.c > @@ -104,11 +104,7 @@ void update_vsyscall(struct timekeeper *tk) > vdso_ts->sec = tk->xtime_sec + tk->wall_to_monotonic.tv_sec; > nsec = tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift; > nsec = nsec + tk->wall_to_monotonic.tv_nsec; > - while (nsec >= NSEC_PER_SEC) { > - nsec = nsec - NSEC_PER_SEC; > - vdso_ts->sec++; > - } > - vdso_ts->nsec = nsec; > + vdso_ts->sec += __iter_div_u64_rem(nsec, NSEC_PER_SEC, &vdso_ts->nsec); > > if (__arch_use_vsyscall(vdata)) > update_vdso_data(vdata, tk); > I am trying to test this patch using clang-9 tip: # clang -v clang version 9.0.0 (git@github.com:llvm-mirror/clang.git 6ed0749151866894a67a3e7eefdc1f3a547daa0e) (git@github.com:llvm-mirror/llvm.git a10a70238ace1093cad3adeb94814b422bd1b5c1) but I get a lot of errors similar to the one below: In file included from ~/linux/arch/x86/events/amd/core.c:11: ~/linux/arch/x86/events/amd/../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); ^ ~/linux/include/linux/percpu-defs.h:447:2: note: expanded from macro '__this_cpu_read' raw_cpu_read(pcp); \ ^ ~/linux/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) ^ ~/linux/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>:110:1: note: expanded from here raw_cpu_read_1 ^ ~/linux/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) ^ ~/linux/arch/x86/include/asm/percpu.h:189:15: note: expanded from macro 'percpu_from_op' : "=q" (pfo_ret__) \ 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 -- Regards, Vincenzo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] vsyscall: use __iter_div_u64_rem() 2019-07-11 12:14 ` Vincenzo Frascino @ 2019-07-11 12:28 ` Arnd Bergmann 2019-07-11 13:08 ` Vincenzo Frascino 2019-07-11 17:14 ` Nick Desaulniers 0 siblings, 2 replies; 7+ messages in thread From: Arnd Bergmann @ 2019-07-11 12:28 UTC (permalink / raw) To: Vincenzo Frascino Cc: linux-arch, Shuah Khan, Linux Kernel Mailing List, Andy Lutomirski, Dmitry Safonov, Huw Davies, Catalin Marinas, Daniel Lezcano, Will Deacon, linux-mips, Ralf Baechle, Russell King, clang-built-linux, Paul Burton, open list:KERNEL SELFTEST FRAMEWORK, Rasmus Villemoes, Thomas Gleixner, Mark Salyzyn, Peter Collingbourne, Linux ARM On Thu, Jul 11, 2019 at 2:14 PM Vincenzo Frascino <vincenzo.frascino@arm.com> 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@suse.com> Signed-off-by: Arnd Bergmann <arnd@arndb.de> 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: \ _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] vsyscall: use __iter_div_u64_rem() 2019-07-11 12:28 ` Arnd Bergmann @ 2019-07-11 13:08 ` Vincenzo Frascino 2019-07-11 17:14 ` Nick Desaulniers 1 sibling, 0 replies; 7+ messages in thread From: Vincenzo Frascino @ 2019-07-11 13:08 UTC (permalink / raw) To: Arnd Bergmann Cc: linux-arch, Shuah Khan, Linux Kernel Mailing List, Andy Lutomirski, Dmitry Safonov, Huw Davies, Catalin Marinas, Daniel Lezcano, Will Deacon, linux-mips, Ralf Baechle, Russell King, clang-built-linux, Paul Burton, open list:KERNEL SELFTEST FRAMEWORK, Rasmus Villemoes, Thomas Gleixner, Mark Salyzyn, Peter Collingbourne, Linux ARM Hi Arnd, On 11/07/2019 13:28, Arnd Bergmann wrote: > On Thu, Jul 11, 2019 at 2:14 PM Vincenzo Frascino > <vincenzo.frascino@arm.com> 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@suse.com> > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > > 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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] vsyscall: use __iter_div_u64_rem() 2019-07-11 12:28 ` Arnd Bergmann 2019-07-11 13:08 ` Vincenzo Frascino @ 2019-07-11 17:14 ` Nick Desaulniers 2019-07-11 20:55 ` Arnd Bergmann 1 sibling, 1 reply; 7+ messages in thread From: Nick Desaulniers @ 2019-07-11 17:14 UTC (permalink / raw) To: Arnd Bergmann Cc: linux-arch, Shuah Khan, Linux Kernel Mailing List, open list:KERNEL SELFTEST FRAMEWORK, Dmitry Safonov, Mark Salyzyn, Huw Davies, Catalin Marinas, Daniel Lezcano, Will Deacon, linux-mips, Ralf Baechle, Russell King, clang-built-linux, Paul Burton, Andy Lutomirski, Rasmus Villemoes, Thomas Gleixner, Vincenzo Frascino, Peter Collingbourne, Linux ARM On Thu, Jul 11, 2019 at 5:28 AM Arnd Bergmann <arnd@arndb.de> wrote: > clang does not like an inline assembly with a "=q" contraint for > a 64-bit output: Seems like starting in GCC 7, GCC may not like it either: https://godbolt.org/z/UyBUfh it simply warns then proceeds with code gen. Another difference may come from when GCC vs Clang perform dead code elimination (DCE) vs semantic analysis. -- Thanks, ~Nick Desaulniers _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] vsyscall: use __iter_div_u64_rem() 2019-07-11 17:14 ` Nick Desaulniers @ 2019-07-11 20:55 ` Arnd Bergmann 0 siblings, 0 replies; 7+ messages in thread From: Arnd Bergmann @ 2019-07-11 20:55 UTC (permalink / raw) To: Nick Desaulniers Cc: linux-arch, Shuah Khan, Linux Kernel Mailing List, open list:KERNEL SELFTEST FRAMEWORK, Dmitry Safonov, Mark Salyzyn, Huw Davies, Catalin Marinas, Daniel Lezcano, Will Deacon, linux-mips, Ralf Baechle, Russell King, clang-built-linux, Paul Burton, Andy Lutomirski, Rasmus Villemoes, Thomas Gleixner, Vincenzo Frascino, Peter Collingbourne, Linux ARM On Thu, Jul 11, 2019 at 7:14 PM 'Nick Desaulniers' via Clang Built Linux <clang-built-linux@googlegroups.com> wrote: > > On Thu, Jul 11, 2019 at 5:28 AM Arnd Bergmann <arnd@arndb.de> wrote: > > clang does not like an inline assembly with a "=q" contraint for > > a 64-bit output: > > Seems like starting in GCC 7, GCC may not like it either: > https://godbolt.org/z/UyBUfh > it simply warns then proceeds with code gen. Another difference may > come from when GCC vs Clang perform dead code elimination (DCE) vs > semantic analysis. Right, I also had the idea to work around it with a set of __builtin_choos_expr() instead of the switch()/case but did not complete that patch as the percpu code is rather complex and this would touch lots of code. Arnd _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2019-07-11 20:55 UTC | newest] Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2019-07-10 13:01 [PATCH] vsyscall: use __iter_div_u64_rem() Arnd Bergmann 2019-07-10 16:56 ` Nathan Chancellor 2019-07-11 12:14 ` Vincenzo Frascino 2019-07-11 12:28 ` Arnd Bergmann 2019-07-11 13:08 ` Vincenzo Frascino 2019-07-11 17:14 ` Nick Desaulniers 2019-07-11 20:55 ` Arnd Bergmann
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