next-20250909: selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared identifier 'HWCAP_GCS'

next-20250909: selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared identifier 'HWCAP_GCS'

[Naresh Kamboju]

The following build warnings / errors noticed on arm64 defconfig
with clang-20 and gcc-13 toolchains on the Linux next-20250909
till next-20250911 tag while building selftests/arm64.

Regression Analysis:
- New regression? Yes
- Reproducibility? yes

First seen on  next-20250909
 Good: next-20250908
 Bad: next-20250909 till next-20250911

Test regression: next-20250909:
selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared
identifier 'HWCAP_GCS'

Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>

## Build log
selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared
identifier 'HWCAP_GCS'
  390 |         if (!(getauxval(AT_HWCAP) & HWCAP_GCS))
      |                                     ^
1 error generated.

The suspected commit pointing to,
  kselftest/arm64/gcs: Use nolibc's getauxval()
  a985fe638344492727528e52416211dda1c391d5


## Source
* Kernel version: 6.17.0-rc5
* Git tree: https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next.git
* Git describe: 6.17.0-rc5-next-20250911
* Git commit: 8f21d9da46702c4d6951ba60ca8a05f42870fe8f
* Architectures: arm64
* Toolchains: gcc-13 and clang-20
* Kconfigs: defconfig

## Build
* Build log: https://qa-reports.linaro.org/api/testruns/29827060/log_file/
* Build details:
https://regressions.linaro.org/lkft/linux-next-master/next-20250909/log-parser-build-clang/clang-compiler-basic-gcs_c-error-use-of-undeclared-identifier-hwcap_gcs/
* Build plan: https://tuxapi.tuxsuite.com/v1/groups/linaro/projects/lkft/builds/32RzudgbCUiqGUoFtquJ9IEIDXZ
* Build link: https://storage.tuxsuite.com/public/linaro/lkft/builds/32RzudgbCUiqGUoFtquJ9IEIDXZ/
* Kernel config:
https://storage.tuxsuite.com/public/linaro/lkft/builds/32RzudgbCUiqGUoFtquJ9IEIDXZ/config

## Steps to reproduce
 $ tuxmake --runtime podman --target-arch arm64 \
 --toolchain clang-nightly \
 --kconfig https://storage.tuxsuite.com/public/linaro/lkft/builds/32RzudgbCUiqGUoFtquJ9IEIDXZ/config
\
 LLVM=1 LLVM_IAS=1 debugkernel dtbs dtbs-legacy headers kernel kselftest modules

--
Linaro LKFT

Re: next-20250909: selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared identifier 'HWCAP_GCS'

[Mark Brown]

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On Fri, Sep 12, 2025 at 12:48:47AM +0530, Naresh Kamboju wrote:
> The following build warnings / errors noticed on arm64 defconfig
> with clang-20 and gcc-13 toolchains on the Linux next-20250909
> till next-20250911 tag while building selftests/arm64.
> 
> Regression Analysis:
> - New regression? Yes
> - Reproducibility? yes
> 
> First seen on  next-20250909
>  Good: next-20250908
>  Bad: next-20250909 till next-20250911
> 
> Test regression: next-20250909:
> selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared
> identifier 'HWCAP_GCS'

This will be due to Thomas Weißschuh's nolibc changes which went in
during that time period and did change the program to use nolibc's
getauxval, presumably that's broken with this clang version or
something?

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Re: next-20250909: selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared identifier 'HWCAP_GCS'

[Thomas Weißschuh]

Hi Naresh,

On 2025-09-12 00:48:47+0530, Naresh Kamboju wrote:
> The following build warnings / errors noticed on arm64 defconfig
> with clang-20 and gcc-13 toolchains on the Linux next-20250909
> till next-20250911 tag while building selftests/arm64.
> 
> Regression Analysis:
> - New regression? Yes
> - Reproducibility? yes
> 
> First seen on  next-20250909
>  Good: next-20250908
>  Bad: next-20250909 till next-20250911
> 
> Test regression: next-20250909:
> selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared
> identifier 'HWCAP_GCS'
> 
> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> 
> ## Build log
> selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared
> identifier 'HWCAP_GCS'
>   390 |         if (!(getauxval(AT_HWCAP) & HWCAP_GCS))
>       |                                     ^
> 1 error generated.
> 
> The suspected commit pointing to,
>   kselftest/arm64/gcs: Use nolibc's getauxval()
>   a985fe638344492727528e52416211dda1c391d5

That suspicion looks correct. I am wondering a bit how this works for
the other selftests which use this symbol.

Can you give this one a try:

diff --git a/tools/testing/selftests/arm64/gcs/gcs-util.h b/tools/testing/selftests/arm64/gcs/gcs-util.h
index c99a6b39ac14..816b497634d6 100644
--- a/tools/testing/selftests/arm64/gcs/gcs-util.h
+++ b/tools/testing/selftests/arm64/gcs/gcs-util.h
@@ -26,6 +26,10 @@ struct user_gcs {
 };
 #endif

+#ifndef HWCAP_GCS
+#define HWCAP_GCS (1UL << 32)
+#endif
+
 /* Shadow Stack/Guarded Control Stack interface */
 #define PR_GET_SHADOW_STACK_STATUS     74
 #define PR_SET_SHADOW_STACK_STATUS      75

Re: next-20250909: selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared identifier 'HWCAP_GCS'

[Naresh Kamboju]

Hi Thomas,

On Fri, 12 Sept 2025 at 12:00, Thomas Weißschuh <linux@weissschuh.net> wrote:
>
> Hi Naresh,
>
> On 2025-09-12 00:48:47+0530, Naresh Kamboju wrote:
> > The following build warnings / errors noticed on arm64 defconfig
> > with clang-20 and gcc-13 toolchains on the Linux next-20250909
> > till next-20250911 tag while building selftests/arm64.
> >
> > Regression Analysis:
> > - New regression? Yes
> > - Reproducibility? yes
> >
> > First seen on  next-20250909
> >  Good: next-20250908
> >  Bad: next-20250909 till next-20250911
> >
> > Test regression: next-20250909:
> > selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared
> > identifier 'HWCAP_GCS'
> >
> > Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> >
> > ## Build log
> > selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared
> > identifier 'HWCAP_GCS'
> >   390 |         if (!(getauxval(AT_HWCAP) & HWCAP_GCS))
> >       |                                     ^
> > 1 error generated.
> >
> > The suspected commit pointing to,
> >   kselftest/arm64/gcs: Use nolibc's getauxval()
> >   a985fe638344492727528e52416211dda1c391d5
>
> That suspicion looks correct. I am wondering a bit how this works for
> the other selftests which use this symbol.
>
> Can you give this one a try:
>

I have applied this patch and tested and reported build regressions
got fixed.

Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>

> diff --git a/tools/testing/selftests/arm64/gcs/gcs-util.h b/tools/testing/selftests/arm64/gcs/gcs-util.h
> index c99a6b39ac14..816b497634d6 100644
> --- a/tools/testing/selftests/arm64/gcs/gcs-util.h
> +++ b/tools/testing/selftests/arm64/gcs/gcs-util.h
> @@ -26,6 +26,10 @@ struct user_gcs {
>  };
>  #endif
>
> +#ifndef HWCAP_GCS
> +#define HWCAP_GCS (1UL << 32)
> +#endif
> +
>  /* Shadow Stack/Guarded Control Stack interface */
>  #define PR_GET_SHADOW_STACK_STATUS     74
>  #define PR_SET_SHADOW_STACK_STATUS      75

--
Linaro LKFT

Re: next-20250909: selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared identifier 'HWCAP_GCS'

[Mark Brown]

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On Fri, Sep 12, 2025 at 08:30:08AM +0200, Thomas Weißschuh wrote:
> On 2025-09-12 00:48:47+0530, Naresh Kamboju wrote:

> index c99a6b39ac14..816b497634d6 100644
> --- a/tools/testing/selftests/arm64/gcs/gcs-util.h
> +++ b/tools/testing/selftests/arm64/gcs/gcs-util.h
> @@ -26,6 +26,10 @@ struct user_gcs {
>  };
>  #endif
> 
> +#ifndef HWCAP_GCS
> +#define HWCAP_GCS (1UL << 32)
> +#endif
> +

We're doing that for glibc using tests because there's some unfortunate
interaction between including the relevant kernel header and glibc's
headers (I forget the details) which means that including the kernel
header directly conflicts with something glibc is doing.  For nolibc I
would expect us to using the kernel's hwcap definitions?

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Re: next-20250909: selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared identifier 'HWCAP_GCS'

[Thomas Weißschuh]

Sep 12, 2025 12:49:58 Mark Brown <broonie@kernel.org>:

> On Fri, Sep 12, 2025 at 08:30:08AM +0200, Thomas Weißschuh wrote:
>> On 2025-09-12 00:48:47+0530, Naresh Kamboju wrote:
>
>> index c99a6b39ac14..816b497634d6 100644
>> --- a/tools/testing/selftests/arm64/gcs/gcs-util.h
>> +++ b/tools/testing/selftests/arm64/gcs/gcs-util.h
>> @@ -26,6 +26,10 @@ struct user_gcs {
>> };
>> #endif
>>
>> +#ifndef HWCAP_GCS
>> +#define HWCAP_GCS (1UL << 32)
>> +#endif
>> +
>
> We're doing that for glibc using tests because there's some unfortunate
> interaction between including the relevant kernel header and glibc's
> headers (I forget the details) which means that including the kernel
> header directly conflicts with something glibc is doing.  For nolibc I
> would expect us to using the kernel's hwcap definitions?

nolibc doesn't even have its own asm/hwcap.h (or any asm/ header for that matter).
So a kernel header has to be used,
maybe an old one is pulled from somewhere?

(I won't have access to a development machine today anymore)

Thomas

Re: next-20250909: selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared identifier 'HWCAP_GCS'

[Thomas Weißschuh]

Sep 12, 2025 12:57:15 Thomas Weißschuh <linux@weissschuh.net>:

> Sep 12, 2025 12:49:58 Mark Brown <broonie@kernel.org>:
>
>> On Fri, Sep 12, 2025 at 08:30:08AM +0200, Thomas Weißschuh wrote:
>>> On 2025-09-12 00:48:47+0530, Naresh Kamboju wrote:
>>
>>> index c99a6b39ac14..816b497634d6 100644
>>> --- a/tools/testing/selftests/arm64/gcs/gcs-util.h
>>> +++ b/tools/testing/selftests/arm64/gcs/gcs-util.h
>>> @@ -26,6 +26,10 @@ struct user_gcs {
>>> };
>>> #endif
>>>
>>> +#ifndef HWCAP_GCS
>>> +#define HWCAP_GCS (1UL << 32)
>>> +#endif
>>> +
>>
>> We're doing that for glibc using tests because there's some unfortunate
>> interaction between including the relevant kernel header and glibc's
>> headers (I forget the details) which means that including the kernel
>> header directly conflicts with something glibc is doing.  For nolibc I
>> would expect us to using the kernel's hwcap definitions?
>
> nolibc doesn't even have its own asm/hwcap.h (or any asm/ header for that matter).
> So a kernel header has to be used,
> maybe an old one is pulled from somewhere?


The Makefile does *not* use -nostdinc, so the nolibc program probably finds the toolchain's glibc asm/hwcap.h.
There also doesn't seem to be a static arm64 hwcap header in tools/include in the first place.
I am still wondering how this works for the other tests.


Thomas

Re: next-20250909: selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared identifier 'HWCAP_GCS'

[Mark Brown]

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On Fri, Sep 12, 2025 at 01:07:58PM +0200, Thomas Weißschuh wrote:

> The Makefile does *not* use -nostdinc, so the nolibc program probably finds the toolchain's glibc asm/hwcap.h.
> There also doesn't seem to be a static arm64 hwcap header in tools/include in the first place.
> I am still wondering how this works for the other tests.

make headers_install puts a copy in usr/include, probably we just need
to include that in the include path.

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Re: next-20250909: selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared identifier 'HWCAP_GCS'

[Thomas Weißschuh]

On 2025-09-12 12:14:00+0100, Mark Brown wrote:
> On Fri, Sep 12, 2025 at 01:07:58PM +0200, Thomas Weißschuh wrote:
> 
> > The Makefile does *not* use -nostdinc, so the nolibc program probably finds the toolchain's glibc asm/hwcap.h.
> > There also doesn't seem to be a static arm64 hwcap header in tools/include in the first place.
> > I am still wondering how this works for the other tests.
> 
> make headers_install puts a copy in usr/include, probably we just need
> to include that in the include path.

Naresh, could you test the patch below?
The other custom $(CC) rules in the gcs directory are also not
respecting $(CFLAGS), but I'll leave these for now.

diff --git a/tools/testing/selftests/arm64/gcs/Makefile b/tools/testing/selftests/arm64/gcs/Makefile
index d2f3497a9..1fbbf0ca1 100644
--- a/tools/testing/selftests/arm64/gcs/Makefile
+++ b/tools/testing/selftests/arm64/gcs/Makefile
@@ -14,11 +14,11 @@ LDLIBS+=-lpthread
 include ../../lib.mk

 $(OUTPUT)/basic-gcs: basic-gcs.c
-       $(CC) -g -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib \
-               -static -include ../../../../include/nolibc/nolibc.h \
+       $(CC) $(CFLAGS) -fno-asynchronous-unwind-tables -fno-ident -s -nostdlib -nostdinc \
+               -static -I../../../../include/nolibc -include ../../../../include/nolibc/nolibc.h \
                -I../../../../../usr/include \
                -std=gnu99 -I../.. -g \
-               -ffreestanding -Wall $^ -o $@ -lgcc
+               -ffreestanding $^ -o $@ -lgcc

 $(OUTPUT)/gcs-stress-thread: gcs-stress-thread.S
        $(CC) -nostdlib $^ -o $@

Re: next-20250909: selftests/arm64/gcs/basic-gcs.c:390:30: error: use of undeclared identifier 'HWCAP_GCS'

[Naresh Kamboju]

On Mon, 15 Sept 2025 at 14:53, Thomas Weißschuh <linux@weissschuh.net> wrote:
>
> On 2025-09-12 12:14:00+0100, Mark Brown wrote:
> > On Fri, Sep 12, 2025 at 01:07:58PM +0200, Thomas Weißschuh wrote:
> >
> > > The Makefile does *not* use -nostdinc, so the nolibc program probably finds the toolchain's glibc asm/hwcap.h.
> > > There also doesn't seem to be a static arm64 hwcap header in tools/include in the first place.
> > > I am still wondering how this works for the other tests.
> >
> > make headers_install puts a copy in usr/include, probably we just need
> > to include that in the include path.
>
> Naresh, could you test the patch below?
> The other custom $(CC) rules in the gcs directory are also not
> respecting $(CFLAGS), but I'll leave these for now.

I have applied this patch on top of Linux next-20250912 tag and
tested and reported build regressions got fixed.

Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>

> diff --git a/tools/testing/selftests/arm64/gcs/Makefile b/tools/testing/selftests/arm64/gcs/Makefile
> index d2f3497a9..1fbbf0ca1 100644
> --- a/tools/testing/selftests/arm64/gcs/Makefile
> +++ b/tools/testing/selftests/arm64/gcs/Makefile
> @@ -14,11 +14,11 @@ LDLIBS+=-lpthread
>  include ../../lib.mk
>
>  $(OUTPUT)/basic-gcs: basic-gcs.c
> -       $(CC) -g -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib \
> -               -static -include ../../../../include/nolibc/nolibc.h \
> +       $(CC) $(CFLAGS) -fno-asynchronous-unwind-tables -fno-ident -s -nostdlib -nostdinc \
> +               -static -I../../../../include/nolibc -include ../../../../include/nolibc/nolibc.h \
>                 -I../../../../../usr/include \
>                 -std=gnu99 -I../.. -g \
> -               -ffreestanding -Wall $^ -o $@ -lgcc
> +               -ffreestanding $^ -o $@ -lgcc
>
>  $(OUTPUT)/gcs-stress-thread: gcs-stress-thread.S
>         $(CC) -nostdlib $^ -o $@
>

- Naresh