Messages in this thread Patch in this message | | | Date | Sun, 23 Aug 2020 23:54:38 +0300 (MSK) | From | Alexander Monakov <> | Subject | Re: [PATCH] tools/power turbostat: call pread64 in kernel directly |
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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:
---8<---
From: Alexander Monakov <amonakov@ispras.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@ispras.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 -- 2.26.2
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