6.1.159-rc1 regression on building perf

6.1.159-rc1 regression on building perf

[Max Krummenacher]

Hi

Our CI found a regression when cross-compiling perf from the 6.1.159-rc1
sources in a yocto setup for a arm64 based machine.

In file included from .../tools/include/linux/bitmap.h:6,
                 from util/pmu.h:5,
                 from builtin-list.c:14:
.../tools/include/asm-generic/bitsperlong.h:14:2: error: #error
Inconsistent word size. Check asm/bitsperlong.h
   14 | #error Inconsistent word size. Check asm/bitsperlong.h
      |  ^~~~~


I could reproduce this as follows in a simpler setup:

git clone -b linux-6.1.y
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
cd linux-stable-rc/
export ARCH=arm64
export CROSS_COMPILE=aarch64-none-linux-gnu-
make defconfig
make -j$(nproc)
cd tools/perf
make

Reverting commit 4d99bf5f8f74 ("tools bitmap: Add missing
asm-generic/bitsperlong.h include") fixed the build in my setup however
I think that the issue the commit addresses would then reappear, so I
don't know what would be a good way forward.

Regards
Max

P.S.
Checking out Linux 6.6.117-rc1 builds perf.
make NO_LIBELF=1 NO_JEVENTS=1 NO_LIBTRACEEVENT=1

Re: 6.1.159-rc1 regression on building perf

[Sasha Levin]

On Mon, Nov 17, 2025 at 05:00:39PM +0100, Max Krummenacher wrote:
>Hi
>
>Our CI found a regression when cross-compiling perf from the 6.1.159-rc1
>sources in a yocto setup for a arm64 based machine.
>
>In file included from .../tools/include/linux/bitmap.h:6,
>                 from util/pmu.h:5,
>                 from builtin-list.c:14:
>.../tools/include/asm-generic/bitsperlong.h:14:2: error: #error
>Inconsistent word size. Check asm/bitsperlong.h
>   14 | #error Inconsistent word size. Check asm/bitsperlong.h
>      |  ^~~~~
>
>
>I could reproduce this as follows in a simpler setup:
>
>git clone -b linux-6.1.y
>https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
>cd linux-stable-rc/
>export ARCH=arm64
>export CROSS_COMPILE=aarch64-none-linux-gnu-
>make defconfig
>make -j$(nproc)
>cd tools/perf
>make
>
>Reverting commit 4d99bf5f8f74 ("tools bitmap: Add missing
>asm-generic/bitsperlong.h include") fixed the build in my setup however
>I think that the issue the commit addresses would then reappear, so I
>don't know what would be a good way forward.

Thanks for the report! I could reproduce this issue localy.

Could you please try cherry-picking commit 8386f58f8deda on top and seeing if
it solves the issue and your CI passes?

-- 
Thanks,
Sasha

Re: 6.1.159-rc1 regression on building perf

[Max Krummenacher]

Hi Sasha

On Mon, Nov 17, 2025 at 5:27 PM Sasha Levin <sashal@kernel.org> wrote:
>
> On Mon, Nov 17, 2025 at 05:00:39PM +0100, Max Krummenacher wrote:
> >Hi
> >
> >Our CI found a regression when cross-compiling perf from the 6.1.159-rc1
> >sources in a yocto setup for a arm64 based machine.
> >
> >In file included from .../tools/include/linux/bitmap.h:6,
> >                 from util/pmu.h:5,
> >                 from builtin-list.c:14:
> >.../tools/include/asm-generic/bitsperlong.h:14:2: error: #error
> >Inconsistent word size. Check asm/bitsperlong.h
> >   14 | #error Inconsistent word size. Check asm/bitsperlong.h
> >      |  ^~~~~
> >
> >
> >I could reproduce this as follows in a simpler setup:
> >
> >git clone -b linux-6.1.y
> >https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
> >cd linux-stable-rc/
> >export ARCH=arm64
> >export CROSS_COMPILE=aarch64-none-linux-gnu-
> >make defconfig
> >make -j$(nproc)
> >cd tools/perf
> >make
> >
> >Reverting commit 4d99bf5f8f74 ("tools bitmap: Add missing
> >asm-generic/bitsperlong.h include") fixed the build in my setup however
> >I think that the issue the commit addresses would then reappear, so I
> >don't know what would be a good way forward.
>
> Thanks for the report! I could reproduce this issue localy.
>
> Could you please try cherry-picking commit 8386f58f8deda on top and seeing if
> it solves the issue and your CI passes?

Cherry-picking commit 8386f58f8deda makes both my local build in the linux
source tree and the CI setup work as expected.

Thanks for the pointer and fix.

Regards,
Max
>
> --
> Thanks,
> Sasha

Re: 6.1.159-rc1 regression on building perf

[Sasha Levin]

On Mon, Nov 17, 2025 at 06:00:55PM +0100, Max Krummenacher wrote:
>Hi Sasha
>
>On Mon, Nov 17, 2025 at 5:27 PM Sasha Levin <sashal@kernel.org> wrote:
>>
>> On Mon, Nov 17, 2025 at 05:00:39PM +0100, Max Krummenacher wrote:
>> >Hi
>> >
>> >Our CI found a regression when cross-compiling perf from the 6.1.159-rc1
>> >sources in a yocto setup for a arm64 based machine.
>> >
>> >In file included from .../tools/include/linux/bitmap.h:6,
>> >                 from util/pmu.h:5,
>> >                 from builtin-list.c:14:
>> >.../tools/include/asm-generic/bitsperlong.h:14:2: error: #error
>> >Inconsistent word size. Check asm/bitsperlong.h
>> >   14 | #error Inconsistent word size. Check asm/bitsperlong.h
>> >      |  ^~~~~
>> >
>> >
>> >I could reproduce this as follows in a simpler setup:
>> >
>> >git clone -b linux-6.1.y
>> >https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
>> >cd linux-stable-rc/
>> >export ARCH=arm64
>> >export CROSS_COMPILE=aarch64-none-linux-gnu-
>> >make defconfig
>> >make -j$(nproc)
>> >cd tools/perf
>> >make
>> >
>> >Reverting commit 4d99bf5f8f74 ("tools bitmap: Add missing
>> >asm-generic/bitsperlong.h include") fixed the build in my setup however
>> >I think that the issue the commit addresses would then reappear, so I
>> >don't know what would be a good way forward.
>>
>> Thanks for the report! I could reproduce this issue localy.
>>
>> Could you please try cherry-picking commit 8386f58f8deda on top and seeing if
>> it solves the issue and your CI passes?
>
>Cherry-picking commit 8386f58f8deda makes both my local build in the linux
>source tree and the CI setup work as expected.
>
>Thanks for the pointer and fix.

Great, I'll queue it up.

Thanks for reporting and testing!

-- 
Thanks,
Sasha

Re: 6.1.159-rc1 regression on building perf

[Ian Rogers]

On Mon, Nov 17, 2025 at 8:00 AM Max Krummenacher <max.oss.09@gmail.com> wrote:
>
> Hi
>
> Our CI found a regression when cross-compiling perf from the 6.1.159-rc1
> sources in a yocto setup for a arm64 based machine.
>
> In file included from .../tools/include/linux/bitmap.h:6,
>                  from util/pmu.h:5,
>                  from builtin-list.c:14:
> .../tools/include/asm-generic/bitsperlong.h:14:2: error: #error
> Inconsistent word size. Check asm/bitsperlong.h
>    14 | #error Inconsistent word size. Check asm/bitsperlong.h
>       |  ^~~~~
>
>
> I could reproduce this as follows in a simpler setup:
>
> git clone -b linux-6.1.y
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
> cd linux-stable-rc/
> export ARCH=arm64
> export CROSS_COMPILE=aarch64-none-linux-gnu-
> make defconfig
> make -j$(nproc)
> cd tools/perf
> make
>
> Reverting commit 4d99bf5f8f74 ("tools bitmap: Add missing
> asm-generic/bitsperlong.h include") fixed the build in my setup however
> I think that the issue the commit addresses would then reappear, so I
> don't know what would be a good way forward.

Hi,

To my knowledge the build issue fixed by 4d99bf5f8f74 ("tools bitmap:
Add missing asm-generic/bitsperlong.h include") only showed up in
Google's build infrastructure. Doing the revert should be fine, but
when you move forward to a newer kernel the issue will reappear. Tbh,
I think there is a lot of cruft in areas like this. The perf tool is
using linux/types.h to have code that's interchangeable with the
kernel, but we could just use stdint.h and be more C compatible. The
version of something like types.h that perf uses matches the kernel
version and not the UAPI version. The use of IS_ERR (and err pointers)
is just copying bad kernel code into user land, we should just use
errno, etc.

Why this issue appears in 6.1 and not 6.6, that's also confusing to me.

Looking at the error in the code:
```
#ifdef __SIZEOF_LONG__
#define BITS_PER_LONG (__CHAR_BIT__ * __SIZEOF_LONG__)
#else
#define BITS_PER_LONG __WORDSIZE
#endif

#if BITS_PER_LONG != __BITS_PER_LONG
#error Inconsistent word size. Check asm/bitsperlong.h
#endif
```

It would be interesting to see where __BITS_PER_LONG is coming from.
You can make the build verbose with V=1 and then run the CC command
with -E to gather details. My suspicion is that we've gotten a muddle
of your system's header files and those in perf, due to the include
order, etc. and the resultant combination is why the test fails. It
could be in 6.6 we added an extra header file in the perf tree and the
include order picks that up first there. It may be possible to suggest
that such an addition to tools/include is backported to 6.1.

A final note, the perf tool is backward compatible with old kernels
and so it should be fine to just have the latest perf and run it on an
old kernel.

Thanks,
Ian

> Regards
> Max
>
> P.S.
> Checking out Linux 6.6.117-rc1 builds perf.
> make NO_LIBELF=1 NO_JEVENTS=1 NO_LIBTRACEEVENT=1