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Date: Mon, 24 Aug 2020 12:08:52 +0800 From: Liwei Song <liwei.song@...driver.com> To: Alexander Monakov <amonakov@...ras.ru>, Len Brown <lenb@...nel.org> CC: Linux PM list <linux-pm@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] tools/power turbostat: call pread64 in kernel directly On 8/24/20 04:54, Alexander Monakov wrote: > Hi, > > I am not the original submitter, but I have answers and a proper patch :) > > On Fri, 21 Aug 2020, Len Brown wrote: > >> Re: offset size >> >> The offsets on this file are the MSR offsets. >> What MSR are you trying to access at offset 0xc0010299? > > This MSR is particular is part of AMD RAPL (energy measurements) interface. > >> Re: pread vs pread64 >> >> If I take on faith that you have some kind of 32-bit execution >> environment that makes pread into pread32 instead of pread64, and that >> truncates an off_t to 32-bits from 64-bits, and it actually makes >> sense to request a read at this large offset... > > The problem here stems from the backward compatibility in Glibc: off_t is > 32-bit on 32-bit x86, unless compiled with -D_FILE_OFFSET_BITS=64. This > macro should be used for all new code. Distros should enable it for all > builds, but when one builds turbostat 'by hand', they hit the issue. > >> would we really have to invoke syscall() directly -- couldn't we >> invoke pread64() directly? (eg. below) > > No, the proper fix is to pass -D_FILE_OFFSET_BITS=64 to the compiler. > > Here's the patch: This path works with my case. Thanks, Liwei. > > ---8<--- > > From: Alexander Monakov <amonakov@...ras.ru> > Date: Sun, 23 Aug 2020 23:27:02 +0300 > Subject: [PATCH] turbostat: build with _FILE_OFFSET_BITS=64 > > For compatibility reasons, Glibc off_t is a 32-bit type on 32-bit x86 > unless _FILE_OFFSET_BITS=64 is defined. Add this define, as otherwise > reading MSRs with index 0x80000000 and above attempts a pread with a > negative offset, which fails. > > Signed-off-by: Alexander Monakov <amonakov@...ras.ru> > --- > tools/power/x86/turbostat/Makefile | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/tools/power/x86/turbostat/Makefile b/tools/power/x86/turbostat/Makefile > index 2b6551269e43..40ae44402eec 100644 > --- a/tools/power/x86/turbostat/Makefile > +++ b/tools/power/x86/turbostat/Makefile > @@ -12,6 +12,7 @@ turbostat : turbostat.c > override CFLAGS += -O2 -Wall -I../../../include > override CFLAGS += -DMSRHEADER='"../../../../arch/x86/include/asm/msr-index.h"' > override CFLAGS += -DINTEL_FAMILY_HEADER='"../../../../arch/x86/include/asm/intel-family.h"' > +override CFLAGS += -D_FILE_OFFSET_BITS=64 > override CFLAGS += -D_FORTIFY_SOURCE=2 > > %: %.c >
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