tools/power turbostat: call pread64 in kernel directly
diff mbox series

Message ID 20200717060849.12469-1-liwei.song@windriver.com
State Superseded, archived
Delegated to: Len Brown
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Series
  • tools/power turbostat: call pread64 in kernel directly
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Commit Message

Liwei Song July 17, 2020, 6:08 a.m. UTC
with 32-bit rootfs, the offset may out of range when set it
to 0xc0010299, define it as "unsigned long long" type and
call pread64 directly in kernel.

Signed-off-by: Liwei Song <liwei.song@windriver.com>
---
 tools/power/x86/turbostat/turbostat.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Comments

Len Brown Aug. 13, 2020, 9:43 p.m. UTC | #1
Huh?

On Fri, Jul 17, 2020 at 2:09 AM Liwei Song <liwei.song@windriver.com> wrote:
>
> with 32-bit rootfs, the offset may out of range when set it
> to 0xc0010299, define it as "unsigned long long" type and
> call pread64 directly in kernel.
>
> Signed-off-by: Liwei Song <liwei.song@windriver.com>
> ---
>  tools/power/x86/turbostat/turbostat.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
> index 33b370865d16..4c5cdfcb5721 100644
> --- a/tools/power/x86/turbostat/turbostat.c
> +++ b/tools/power/x86/turbostat/turbostat.c
> @@ -33,6 +33,7 @@
>  #include <sys/capability.h>
>  #include <errno.h>
>  #include <math.h>
> +#include <sys/syscall.h>
>
>  char *proc_stat = "/proc/stat";
>  FILE *outf;
> @@ -381,11 +382,11 @@ int get_msr_fd(int cpu)
>         return fd;
>  }
>
> -int get_msr(int cpu, off_t offset, unsigned long long *msr)
> +int get_msr(int cpu, unsigned long long offset, unsigned long long *msr)
>  {
>         ssize_t retval;
>
> -       retval = pread(get_msr_fd(cpu), msr, sizeof(*msr), offset);
> +       retval = syscall(SYS_pread64, get_msr_fd(cpu), msr, sizeof(*msr), offset);
>
>         if (retval != sizeof *msr)
>                 err(-1, "cpu%d: msr offset 0x%llx read failed", cpu, (unsigned long long)offset);
> --
> 2.17.1
>
Liwei Song Aug. 14, 2020, 2:17 a.m. UTC | #2
with multilib lib32 support, the rootfs will be 32-bit, 
the kernel is still 64-bit, in this case run turbostat
will failed with "out of range" error.

Thanks,
Liwei.

On 8/14/20 05:43, Len Brown wrote:
> Huh?
> 
> On Fri, Jul 17, 2020 at 2:09 AM Liwei Song <liwei.song@windriver.com> wrote:
>>
>> with 32-bit rootfs, the offset may out of range when set it
>> to 0xc0010299, define it as "unsigned long long" type and
>> call pread64 directly in kernel.
>>
>> Signed-off-by: Liwei Song <liwei.song@windriver.com>
>> ---
>>  tools/power/x86/turbostat/turbostat.c | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
>> index 33b370865d16..4c5cdfcb5721 100644
>> --- a/tools/power/x86/turbostat/turbostat.c
>> +++ b/tools/power/x86/turbostat/turbostat.c
>> @@ -33,6 +33,7 @@
>>  #include <sys/capability.h>
>>  #include <errno.h>
>>  #include <math.h>
>> +#include <sys/syscall.h>
>>
>>  char *proc_stat = "/proc/stat";
>>  FILE *outf;
>> @@ -381,11 +382,11 @@ int get_msr_fd(int cpu)
>>         return fd;
>>  }
>>
>> -int get_msr(int cpu, off_t offset, unsigned long long *msr)
>> +int get_msr(int cpu, unsigned long long offset, unsigned long long *msr)
>>  {
>>         ssize_t retval;
>>
>> -       retval = pread(get_msr_fd(cpu), msr, sizeof(*msr), offset);
>> +       retval = syscall(SYS_pread64, get_msr_fd(cpu), msr, sizeof(*msr), offset);
>>
>>         if (retval != sizeof *msr)
>>                 err(-1, "cpu%d: msr offset 0x%llx read failed", cpu, (unsigned long long)offset);
>> --
>> 2.17.1
>>
> 
>
Len Brown Aug. 21, 2020, 6:50 p.m. UTC | #3
Re: offset size

The offsets on this file are the MSR offsets.
What MSR are you trying to access at offset 0xc0010299?

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...

would we really have to invoke syscall() directly -- couldn't we
invoke pread64() directly? (eg. below)

thanks,
-Len


@@ -490,11 +491,12 @@ int get_msr_fd(int cpu)
        return fd;
 }

-int get_msr(int cpu, off_t offset, unsigned long long *msr)
+int get_msr(int cpu, unsigned long long offset, unsigned long long *msr)
 {
        ssize_t retval;

-       retval = pread(get_msr_fd(cpu), msr, sizeof(*msr), offset);
+       retval = pread64(get_msr_fd(cpu), msr, sizeof(*msr), offset);

        if (retval != sizeof *msr)
                err(-1, "cpu%d: msr offset 0x%llx read failed", cpu,
(unsigned long long)offset);

On Thu, Aug 13, 2020 at 10:17 PM Liwei Song <liwei.song@windriver.com> wrote:
>
> with multilib lib32 support, the rootfs will be 32-bit,
> the kernel is still 64-bit, in this case run turbostat
> will failed with "out of range" error.
>
> Thanks,
> Liwei.
>
> On 8/14/20 05:43, Len Brown wrote:
> > Huh?
> >
> > On Fri, Jul 17, 2020 at 2:09 AM Liwei Song <liwei.song@windriver.com> wrote:
> >>
> >> with 32-bit rootfs, the offset may out of range when set it
> >> to 0xc0010299, define it as "unsigned long long" type and
> >> call pread64 directly in kernel.
> >>
> >> Signed-off-by: Liwei Song <liwei.song@windriver.com>
> >> ---
> >>  tools/power/x86/turbostat/turbostat.c | 5 +++--
> >>  1 file changed, 3 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
> >> index 33b370865d16..4c5cdfcb5721 100644
> >> --- a/tools/power/x86/turbostat/turbostat.c
> >> +++ b/tools/power/x86/turbostat/turbostat.c
> >> @@ -33,6 +33,7 @@
> >>  #include <sys/capability.h>
> >>  #include <errno.h>
> >>  #include <math.h>
> >> +#include <sys/syscall.h>
> >>
> >>  char *proc_stat = "/proc/stat";
> >>  FILE *outf;
> >> @@ -381,11 +382,11 @@ int get_msr_fd(int cpu)
> >>         return fd;
> >>  }
> >>
> >> -int get_msr(int cpu, off_t offset, unsigned long long *msr)
> >> +int get_msr(int cpu, unsigned long long offset, unsigned long long *msr)
> >>  {
> >>         ssize_t retval;
> >>
> >> -       retval = pread(get_msr_fd(cpu), msr, sizeof(*msr), offset);
> >> +       retval = syscall(SYS_pread64, get_msr_fd(cpu), msr, sizeof(*msr), offset);
> >>
> >>         if (retval != sizeof *msr)
> >>                 err(-1, "cpu%d: msr offset 0x%llx read failed", cpu, (unsigned long long)offset);
> >> --
> >> 2.17.1
> >>
> >
> >
Alexander Monakov Aug. 23, 2020, 8:54 p.m. UTC | #4
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
Liwei Song Aug. 24, 2020, 4:08 a.m. UTC | #5
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@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
>
Len Brown Sept. 3, 2020, 5:36 p.m. UTC | #6
> -D_FILE_OFFSET_BITS=64

Applied.

thanks!
-Len

On Mon, Aug 24, 2020 at 12:09 AM Liwei Song <liwei.song@windriver.com> wrote:
>
>
>
> 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@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
> >

Patch
diff mbox series

diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
index 33b370865d16..4c5cdfcb5721 100644
--- a/tools/power/x86/turbostat/turbostat.c
+++ b/tools/power/x86/turbostat/turbostat.c
@@ -33,6 +33,7 @@ 
 #include <sys/capability.h>
 #include <errno.h>
 #include <math.h>
+#include <sys/syscall.h>
 
 char *proc_stat = "/proc/stat";
 FILE *outf;
@@ -381,11 +382,11 @@  int get_msr_fd(int cpu)
 	return fd;
 }
 
-int get_msr(int cpu, off_t offset, unsigned long long *msr)
+int get_msr(int cpu, unsigned long long offset, unsigned long long *msr)
 {
 	ssize_t retval;
 
-	retval = pread(get_msr_fd(cpu), msr, sizeof(*msr), offset);
+	retval = syscall(SYS_pread64, get_msr_fd(cpu), msr, sizeof(*msr), offset);
 
 	if (retval != sizeof *msr)
 		err(-1, "cpu%d: msr offset 0x%llx read failed", cpu, (unsigned long long)offset);