[v3,1/4] kbuild: compile-test UAPI headers to ensure they are self-contained
diff mbox series

Message ID 20190627163903.28398-2-yamada.masahiro@socionext.com
State Not Applicable
Delegated to: David Miller
Headers show
Series
  • Compile-test UAPI and kernel headers
Related show

Commit Message

Masahiro Yamada June 27, 2019, 4:38 p.m. UTC
Multiple people have suggested compile-testing UAPI headers to ensure
they can be really included from user-space. "make headers_check" is
obviously not enough to catch bugs, and we often leak references to
kernel-space definition to user-space.

Use the new header-test-y syntax to implement it. Please note exported
headers are compile-tested with a completely different set of compiler
flags. The header search path is set to $(objtree)/usr/include since
exported headers should not include unexported ones.

We use -std=gnu89 for the kernel space since the kernel code highly
depends on GNU extensions. On the other hand, UAPI headers should be
written in more standardized C, so they are compiled with -std=c90.
This will emit errors if C++ style comments, the keyword 'inline', etc.
are used. Please use C style comments (/* ... */), '__inline__', etc.
in UAPI headers.

There is additional compiler requirement to enable this test because
many of UAPI headers include <stdlib.h>, <sys/ioctl.h>, <sys/time.h>,
etc. directly or indirectly. You cannot use kernel.org pre-built
toolchains [1] since they lack <stdlib.h>.

I added scripts/cc-system-headers.sh to check the system header
availability, which CONFIG_UAPI_HEADER_TEST depends on.

For now, a lot of headers need to be excluded because they cannot
be compiled standalone, but this is a good start point.

[1] https://mirrors.edge.kernel.org/pub/tools/crosstool/index.html

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
---

Changes in v3: None
Changes in v2:
 - Add CONFIG_CPU_{BIG,LITTLE}_ENDIAN guard to avoid build error
 - Use 'header-test-' instead of 'no-header-test'
 - Avoid weird 'find' warning when cleaning

 Makefile                     |   2 +-
 init/Kconfig                 |  11 +++
 scripts/cc-system-headers.sh |   8 +++
 usr/.gitignore               |   1 -
 usr/Makefile                 |   2 +
 usr/include/.gitignore       |   3 +
 usr/include/Makefile         | 134 +++++++++++++++++++++++++++++++++++
 7 files changed, 159 insertions(+), 2 deletions(-)
 create mode 100755 scripts/cc-system-headers.sh
 create mode 100644 usr/include/.gitignore
 create mode 100644 usr/include/Makefile

Comments

Sam Ravnborg June 28, 2019, 3:43 p.m. UTC | #1
Hi Masahiro.

On Fri, Jun 28, 2019 at 01:38:59AM +0900, Masahiro Yamada wrote:
> Multiple people have suggested compile-testing UAPI headers to ensure
> they can be really included from user-space. "make headers_check" is
> obviously not enough to catch bugs, and we often leak references to
> kernel-space definition to user-space.
> 
> Use the new header-test-y syntax to implement it. Please note exported
> headers are compile-tested with a completely different set of compiler
> flags. The header search path is set to $(objtree)/usr/include since
> exported headers should not include unexported ones.

This patchset introduce a new set of tests for uapi headers.
Can we somehow consolidate so we have only one way to verify the uapi
headers?
It can be confusing for users that they see errors from testing the
uapi headers during normal build and a new class or error if they
run a "make headers_check" sometimes later.

This can be a next step to consolidate this.
With the suggestions below considered you can add my:
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>

> 
> We use -std=gnu89 for the kernel space since the kernel code highly
> depends on GNU extensions. On the other hand, UAPI headers should be
> written in more standardized C, so they are compiled with -std=c90.
> This will emit errors if C++ style comments, the keyword 'inline', etc.
> are used. Please use C style comments (/* ... */), '__inline__', etc.
> in UAPI headers.
> 
> There is additional compiler requirement to enable this test because
> many of UAPI headers include <stdlib.h>, <sys/ioctl.h>, <sys/time.h>,
> etc. directly or indirectly. You cannot use kernel.org pre-built
> toolchains [1] since they lack <stdlib.h>.
> 
> I added scripts/cc-system-headers.sh to check the system header
> availability, which CONFIG_UAPI_HEADER_TEST depends on.
> 
> For now, a lot of headers need to be excluded because they cannot
> be compiled standalone, but this is a good start point.
> 
> [1] https://mirrors.edge.kernel.org/pub/tools/crosstool/index.html
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> ---
> 
> Changes in v3: None
> Changes in v2:
>  - Add CONFIG_CPU_{BIG,LITTLE}_ENDIAN guard to avoid build error
>  - Use 'header-test-' instead of 'no-header-test'
>  - Avoid weird 'find' warning when cleaning
> 
>  Makefile                     |   2 +-
>  init/Kconfig                 |  11 +++
>  scripts/cc-system-headers.sh |   8 +++
>  usr/.gitignore               |   1 -
>  usr/Makefile                 |   2 +
>  usr/include/.gitignore       |   3 +
>  usr/include/Makefile         | 134 +++++++++++++++++++++++++++++++++++
>  7 files changed, 159 insertions(+), 2 deletions(-)
>  create mode 100755 scripts/cc-system-headers.sh
>  create mode 100644 usr/include/.gitignore
>  create mode 100644 usr/include/Makefile
> 
> diff --git a/Makefile b/Makefile
> index 1f35aca4fe05..f23516980796 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1363,7 +1363,7 @@ CLEAN_DIRS  += $(MODVERDIR) include/ksym
>  CLEAN_FILES += modules.builtin.modinfo
>  
>  # Directories & files removed with 'make mrproper'
> -MRPROPER_DIRS  += include/config usr/include include/generated          \
> +MRPROPER_DIRS  += include/config include/generated          \
>  		  arch/$(SRCARCH)/include/generated .tmp_objdiff
>  MRPROPER_FILES += .config .config.old .version \
>  		  Module.symvers tags TAGS cscope* GPATH GTAGS GRTAGS GSYMS \
> diff --git a/init/Kconfig b/init/Kconfig
> index df5bba27e3fe..667d68e1cdf4 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -105,6 +105,17 @@ config HEADER_TEST
>  	  If you are a developer or tester and want to ensure the requested
>  	  headers are self-contained, say Y here. Otherwise, choose N.
>  
> +config UAPI_HEADER_TEST
> +	bool "Compile test UAPI headers"
> +	depends on HEADER_TEST && HEADERS_INSTALL
> +	depends on $(success,$(srctree)/scripts/cc-system-headers.sh $(CC))
> +	help
> +	  Compile test headers exported to user-space to ensure they are
> +	  self-contained, i.e. compilable as standalone units.
> +
> +	  If you are a developer or tester and want to ensure the exported
> +	  headers are self-contained, say Y here. Otherwise, choose N.
> +
>  config LOCALVERSION
>  	string "Local version - append to kernel release"
>  	help
> diff --git a/scripts/cc-system-headers.sh b/scripts/cc-system-headers.sh
> new file mode 100755
> index 000000000000..1b3db369828c
> --- /dev/null
> +++ b/scripts/cc-system-headers.sh
> @@ -0,0 +1,8 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0-only
> +
> +cat << "END" | $@ -E -x c - -o /dev/null >/dev/null 2>&1
> +#include <stdlib.h>
> +#include <sys/ioctl.h>
> +#include <sys/time.h>
> +END

Add comment to this file that explains that it is used to verify that the
toolchain provides the minimal set of header-files required by uapi
headers.

> diff --git a/usr/.gitignore b/usr/.gitignore
> index 8e48117a3f3d..be5eae1df7eb 100644
> --- a/usr/.gitignore
> +++ b/usr/.gitignore
> @@ -7,4 +7,3 @@ initramfs_data.cpio.gz
>  initramfs_data.cpio.bz2
>  initramfs_data.cpio.lzma
>  initramfs_list
> -include
> diff --git a/usr/Makefile b/usr/Makefile
> index 4a70ae43c9cb..6a89eb019275 100644
> --- a/usr/Makefile
> +++ b/usr/Makefile
> @@ -56,3 +56,5 @@ $(deps_initramfs): klibcdirs
>  $(obj)/$(datafile_y): $(obj)/gen_init_cpio $(deps_initramfs) klibcdirs
>  	$(Q)$(initramfs) -l $(ramfs-input) > $(obj)/$(datafile_d_y)
>  	$(call if_changed,initfs)
> +
> +subdir-$(CONFIG_UAPI_HEADER_TEST) += include
> diff --git a/usr/include/.gitignore b/usr/include/.gitignore
> new file mode 100644
> index 000000000000..a0991ff4402b
> --- /dev/null
> +++ b/usr/include/.gitignore
> @@ -0,0 +1,3 @@
> +*
> +!.gitignore
> +!Makefile
> diff --git a/usr/include/Makefile b/usr/include/Makefile
> new file mode 100644
> index 000000000000..58ce96fa1701
> --- /dev/null
> +++ b/usr/include/Makefile
> @@ -0,0 +1,134 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +
> +# Unlike the kernel space, uapi headers are written in standard C.
> +#  - Forbid C++ style comments
> +#  - Use '__inline__', '__asm__' instead of 'inline', 'asm'
> +#
> +# -std=c90 (equivalent to -ansi) catches the violation of those.
> +# We cannot go as far as adding -Wpedantic since it emits too many warnings.
> +#
> +# REVISIT: re-consider the proper set of compiler flags for uapi compile-test.
> +
> +UAPI_CFLAGS := -std=c90 -Wall -Werror=implicit-function-declaration
> +
> +override c_flags = $(UAPI_CFLAGS) -Wp,-MD,$(depfile) -I$(objtree)/usr/include
> +
> +# The following are excluded for now because they fail to build.
> +# The cause of errors are mostly missing include directives.
> +# Check one by one, and send a patch to each subsystem.
> +#
> +# Do not add a new header to the blacklist without legitimate reason.
> +# Please consider to fix the header first.

Maybe add comment that the alphabetical sort by filename must be preserved.
Not too relevant, as we hopefully do not see files being added.

> +header-test- += asm/ipcbuf.h
> +header-test- += asm/msgbuf.h
Consider same syntax like in include/Makefile where you use
header-test-<tab><tab>...+= file

Then the alignment looks betters.

> +header-test- += asm/sembuf.h
> +header-test- += asm/shmbuf.h
> +header-test- += asm/signal.h
> +header-test- += asm/ucontext.h
> +header-test- += drm/vmwgfx_drm.h
> +header-test- += linux/am437x-vpfe.h
> +header-test- += linux/android/binderfs.h
> +header-test- += linux/android/binder.h
> +header-test-$(CONFIG_CPU_BIG_ENDIAN) += linux/byteorder/big_endian.h
> +header-test-$(CONFIG_CPU_LITTLE_ENDIAN) += linux/byteorder/little_endian.h
> +header-test- += linux/coda.h
...
List is shorter than I feared. Seems quite doable to get down to a
small number of files.

> +
> +# more headers are broken in some architectures
> +
> +ifeq ($(SRCARCH),arc)
> +header-test- += linux/bpf_perf_event.h
> +endif
Again a manageable number.

> +
> +
> +# asm-generic/*.h is used by asm/*.h, and should not be included directly
> +header-test- += asm-generic/%
> +
> +# The rest are compile-tested
> +header-test-y += $(filter-out $(header-test-), \
> +			$(patsubst $(obj)/%,%, $(wildcard \
> +			$(addprefix $(obj)/, *.h */*.h */*/*.h */*/*/*.h))))
Could you use header-test-pattern-y here?

	Sam
Masahiro Yamada June 30, 2019, 1:27 a.m. UTC | #2
Hi Sam,

On Sat, Jun 29, 2019 at 12:44 AM Sam Ravnborg <sam@ravnborg.org> wrote:
>
> Hi Masahiro.
>
> On Fri, Jun 28, 2019 at 01:38:59AM +0900, Masahiro Yamada wrote:
> > Multiple people have suggested compile-testing UAPI headers to ensure
> > they can be really included from user-space. "make headers_check" is
> > obviously not enough to catch bugs, and we often leak references to
> > kernel-space definition to user-space.
> >
> > Use the new header-test-y syntax to implement it. Please note exported
> > headers are compile-tested with a completely different set of compiler
> > flags. The header search path is set to $(objtree)/usr/include since
> > exported headers should not include unexported ones.
>
> This patchset introduce a new set of tests for uapi headers.
> Can we somehow consolidate so we have only one way to verify the uapi
> headers?
> It can be confusing for users that they see errors from testing the
> uapi headers during normal build and a new class or error if they
> run a "make headers_check" sometimes later.

Good point. I had also noticed some over-wrap
between this feature and scripts/headers_check.pl
For example, check_include will be unneeded.

I expect "make headers_check" will be deprecated
sooner or later.


> This can be a next step to consolidate this.
> With the suggestions below considered you can add my:
> Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
>
> >
> > We use -std=gnu89 for the kernel space since the kernel code highly
> > depends on GNU extensions. On the other hand, UAPI headers should be
> > written in more standardized C, so they are compiled with -std=c90.
> > This will emit errors if C++ style comments, the keyword 'inline', etc.
> > are used. Please use C style comments (/* ... */), '__inline__', etc.
> > in UAPI headers.
> >
> > There is additional compiler requirement to enable this test because
> > many of UAPI headers include <stdlib.h>, <sys/ioctl.h>, <sys/time.h>,
> > etc. directly or indirectly. You cannot use kernel.org pre-built
> > toolchains [1] since they lack <stdlib.h>.
> >
> > I added scripts/cc-system-headers.sh to check the system header
> > availability, which CONFIG_UAPI_HEADER_TEST depends on.
> >
> > For now, a lot of headers need to be excluded because they cannot
> > be compiled standalone, but this is a good start point.
> >
> > [1] https://mirrors.edge.kernel.org/pub/tools/crosstool/index.html
> >
> > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> > ---
> >
> > Changes in v3: None
> > Changes in v2:
> >  - Add CONFIG_CPU_{BIG,LITTLE}_ENDIAN guard to avoid build error
> >  - Use 'header-test-' instead of 'no-header-test'
> >  - Avoid weird 'find' warning when cleaning
> >
> >  Makefile                     |   2 +-
> >  init/Kconfig                 |  11 +++
> >  scripts/cc-system-headers.sh |   8 +++
> >  usr/.gitignore               |   1 -
> >  usr/Makefile                 |   2 +
> >  usr/include/.gitignore       |   3 +
> >  usr/include/Makefile         | 134 +++++++++++++++++++++++++++++++++++
> >  7 files changed, 159 insertions(+), 2 deletions(-)
> >  create mode 100755 scripts/cc-system-headers.sh
> >  create mode 100644 usr/include/.gitignore
> >  create mode 100644 usr/include/Makefile
> >
> > diff --git a/Makefile b/Makefile
> > index 1f35aca4fe05..f23516980796 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -1363,7 +1363,7 @@ CLEAN_DIRS  += $(MODVERDIR) include/ksym
> >  CLEAN_FILES += modules.builtin.modinfo
> >
> >  # Directories & files removed with 'make mrproper'
> > -MRPROPER_DIRS  += include/config usr/include include/generated          \
> > +MRPROPER_DIRS  += include/config include/generated          \
> >                 arch/$(SRCARCH)/include/generated .tmp_objdiff
> >  MRPROPER_FILES += .config .config.old .version \
> >                 Module.symvers tags TAGS cscope* GPATH GTAGS GRTAGS GSYMS \
> > diff --git a/init/Kconfig b/init/Kconfig
> > index df5bba27e3fe..667d68e1cdf4 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -105,6 +105,17 @@ config HEADER_TEST
> >         If you are a developer or tester and want to ensure the requested
> >         headers are self-contained, say Y here. Otherwise, choose N.
> >
> > +config UAPI_HEADER_TEST
> > +     bool "Compile test UAPI headers"
> > +     depends on HEADER_TEST && HEADERS_INSTALL
> > +     depends on $(success,$(srctree)/scripts/cc-system-headers.sh $(CC))
> > +     help
> > +       Compile test headers exported to user-space to ensure they are
> > +       self-contained, i.e. compilable as standalone units.
> > +
> > +       If you are a developer or tester and want to ensure the exported
> > +       headers are self-contained, say Y here. Otherwise, choose N.
> > +
> >  config LOCALVERSION
> >       string "Local version - append to kernel release"
> >       help
> > diff --git a/scripts/cc-system-headers.sh b/scripts/cc-system-headers.sh
> > new file mode 100755
> > index 000000000000..1b3db369828c
> > --- /dev/null
> > +++ b/scripts/cc-system-headers.sh
> > @@ -0,0 +1,8 @@
> > +#!/bin/sh
> > +# SPDX-License-Identifier: GPL-2.0-only
> > +
> > +cat << "END" | $@ -E -x c - -o /dev/null >/dev/null 2>&1
> > +#include <stdlib.h>
> > +#include <sys/ioctl.h>
> > +#include <sys/time.h>
> > +END
>
> Add comment to this file that explains that it is used to verify that the
> toolchain provides the minimal set of header-files required by uapi
> headers.

Will do.

> > diff --git a/usr/.gitignore b/usr/.gitignore
> > index 8e48117a3f3d..be5eae1df7eb 100644
> > --- a/usr/.gitignore
> > +++ b/usr/.gitignore
> > @@ -7,4 +7,3 @@ initramfs_data.cpio.gz
> >  initramfs_data.cpio.bz2
> >  initramfs_data.cpio.lzma
> >  initramfs_list
> > -include
> > diff --git a/usr/Makefile b/usr/Makefile
> > index 4a70ae43c9cb..6a89eb019275 100644
> > --- a/usr/Makefile
> > +++ b/usr/Makefile
> > @@ -56,3 +56,5 @@ $(deps_initramfs): klibcdirs
> >  $(obj)/$(datafile_y): $(obj)/gen_init_cpio $(deps_initramfs) klibcdirs
> >       $(Q)$(initramfs) -l $(ramfs-input) > $(obj)/$(datafile_d_y)
> >       $(call if_changed,initfs)
> > +
> > +subdir-$(CONFIG_UAPI_HEADER_TEST) += include
> > diff --git a/usr/include/.gitignore b/usr/include/.gitignore
> > new file mode 100644
> > index 000000000000..a0991ff4402b
> > --- /dev/null
> > +++ b/usr/include/.gitignore
> > @@ -0,0 +1,3 @@
> > +*
> > +!.gitignore
> > +!Makefile
> > diff --git a/usr/include/Makefile b/usr/include/Makefile
> > new file mode 100644
> > index 000000000000..58ce96fa1701
> > --- /dev/null
> > +++ b/usr/include/Makefile
> > @@ -0,0 +1,134 @@
> > +# SPDX-License-Identifier: GPL-2.0-only
> > +
> > +# Unlike the kernel space, uapi headers are written in standard C.
> > +#  - Forbid C++ style comments
> > +#  - Use '__inline__', '__asm__' instead of 'inline', 'asm'
> > +#
> > +# -std=c90 (equivalent to -ansi) catches the violation of those.
> > +# We cannot go as far as adding -Wpedantic since it emits too many warnings.
> > +#
> > +# REVISIT: re-consider the proper set of compiler flags for uapi compile-test.
> > +
> > +UAPI_CFLAGS := -std=c90 -Wall -Werror=implicit-function-declaration
> > +
> > +override c_flags = $(UAPI_CFLAGS) -Wp,-MD,$(depfile) -I$(objtree)/usr/include
> > +
> > +# The following are excluded for now because they fail to build.
> > +# The cause of errors are mostly missing include directives.
> > +# Check one by one, and send a patch to each subsystem.
> > +#
> > +# Do not add a new header to the blacklist without legitimate reason.
> > +# Please consider to fix the header first.
>
> Maybe add comment that the alphabetical sort by filename must be preserved.
> Not too relevant, as we hopefully do not see files being added.
>
> > +header-test- += asm/ipcbuf.h
> > +header-test- += asm/msgbuf.h
> Consider same syntax like in include/Makefile where you use
> header-test-<tab><tab>...+= file
>
> Then the alignment looks betters.

Probably I can do that, but this is not so important
because our ultimate goal is (almost) no blacklist.




> > +
> > +# The rest are compile-tested
> > +header-test-y += $(filter-out $(header-test-), \
> > +                     $(patsubst $(obj)/%,%, $(wildcard \
> > +                     $(addprefix $(obj)/, *.h */*.h */*/*.h */*/*/*.h))))
> Could you use header-test-pattern-y here?

header-test-pattern-y does not work here
because it only matches to $(srctree)/$(src)/*

All headers under usr/include/
are generated one, and located in $(objtree)/$(obj)/.


Thanks.
Masahiro Yamada June 30, 2019, 1:35 a.m. UTC | #3
On Fri, Jun 28, 2019 at 1:40 AM Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
>
> Multiple people have suggested compile-testing UAPI headers to ensure
> they can be really included from user-space. "make headers_check" is
> obviously not enough to catch bugs, and we often leak references to
> kernel-space definition to user-space.
>
> Use the new header-test-y syntax to implement it. Please note exported
> headers are compile-tested with a completely different set of compiler
> flags. The header search path is set to $(objtree)/usr/include since
> exported headers should not include unexported ones.
>
> We use -std=gnu89 for the kernel space since the kernel code highly
> depends on GNU extensions. On the other hand, UAPI headers should be
> written in more standardized C, so they are compiled with -std=c90.
> This will emit errors if C++ style comments, the keyword 'inline', etc.
> are used. Please use C style comments (/* ... */), '__inline__', etc.
> in UAPI headers.
>
> There is additional compiler requirement to enable this test because
> many of UAPI headers include <stdlib.h>, <sys/ioctl.h>, <sys/time.h>,
> etc. directly or indirectly. You cannot use kernel.org pre-built
> toolchains [1] since they lack <stdlib.h>.
>
> I added scripts/cc-system-headers.sh to check the system header
> availability, which CONFIG_UAPI_HEADER_TEST depends on.


Perhaps, we could use scripts/cc-can-link.sh for this purpose.

The intention is slightly different, but a compiler to link
user-space programs must provide necessary standard headers.

Patch
diff mbox series

diff --git a/Makefile b/Makefile
index 1f35aca4fe05..f23516980796 100644
--- a/Makefile
+++ b/Makefile
@@ -1363,7 +1363,7 @@  CLEAN_DIRS  += $(MODVERDIR) include/ksym
 CLEAN_FILES += modules.builtin.modinfo
 
 # Directories & files removed with 'make mrproper'
-MRPROPER_DIRS  += include/config usr/include include/generated          \
+MRPROPER_DIRS  += include/config include/generated          \
 		  arch/$(SRCARCH)/include/generated .tmp_objdiff
 MRPROPER_FILES += .config .config.old .version \
 		  Module.symvers tags TAGS cscope* GPATH GTAGS GRTAGS GSYMS \
diff --git a/init/Kconfig b/init/Kconfig
index df5bba27e3fe..667d68e1cdf4 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -105,6 +105,17 @@  config HEADER_TEST
 	  If you are a developer or tester and want to ensure the requested
 	  headers are self-contained, say Y here. Otherwise, choose N.
 
+config UAPI_HEADER_TEST
+	bool "Compile test UAPI headers"
+	depends on HEADER_TEST && HEADERS_INSTALL
+	depends on $(success,$(srctree)/scripts/cc-system-headers.sh $(CC))
+	help
+	  Compile test headers exported to user-space to ensure they are
+	  self-contained, i.e. compilable as standalone units.
+
+	  If you are a developer or tester and want to ensure the exported
+	  headers are self-contained, say Y here. Otherwise, choose N.
+
 config LOCALVERSION
 	string "Local version - append to kernel release"
 	help
diff --git a/scripts/cc-system-headers.sh b/scripts/cc-system-headers.sh
new file mode 100755
index 000000000000..1b3db369828c
--- /dev/null
+++ b/scripts/cc-system-headers.sh
@@ -0,0 +1,8 @@ 
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+
+cat << "END" | $@ -E -x c - -o /dev/null >/dev/null 2>&1
+#include <stdlib.h>
+#include <sys/ioctl.h>
+#include <sys/time.h>
+END
diff --git a/usr/.gitignore b/usr/.gitignore
index 8e48117a3f3d..be5eae1df7eb 100644
--- a/usr/.gitignore
+++ b/usr/.gitignore
@@ -7,4 +7,3 @@  initramfs_data.cpio.gz
 initramfs_data.cpio.bz2
 initramfs_data.cpio.lzma
 initramfs_list
-include
diff --git a/usr/Makefile b/usr/Makefile
index 4a70ae43c9cb..6a89eb019275 100644
--- a/usr/Makefile
+++ b/usr/Makefile
@@ -56,3 +56,5 @@  $(deps_initramfs): klibcdirs
 $(obj)/$(datafile_y): $(obj)/gen_init_cpio $(deps_initramfs) klibcdirs
 	$(Q)$(initramfs) -l $(ramfs-input) > $(obj)/$(datafile_d_y)
 	$(call if_changed,initfs)
+
+subdir-$(CONFIG_UAPI_HEADER_TEST) += include
diff --git a/usr/include/.gitignore b/usr/include/.gitignore
new file mode 100644
index 000000000000..a0991ff4402b
--- /dev/null
+++ b/usr/include/.gitignore
@@ -0,0 +1,3 @@ 
+*
+!.gitignore
+!Makefile
diff --git a/usr/include/Makefile b/usr/include/Makefile
new file mode 100644
index 000000000000..58ce96fa1701
--- /dev/null
+++ b/usr/include/Makefile
@@ -0,0 +1,134 @@ 
+# SPDX-License-Identifier: GPL-2.0-only
+
+# Unlike the kernel space, uapi headers are written in standard C.
+#  - Forbid C++ style comments
+#  - Use '__inline__', '__asm__' instead of 'inline', 'asm'
+#
+# -std=c90 (equivalent to -ansi) catches the violation of those.
+# We cannot go as far as adding -Wpedantic since it emits too many warnings.
+#
+# REVISIT: re-consider the proper set of compiler flags for uapi compile-test.
+
+UAPI_CFLAGS := -std=c90 -Wall -Werror=implicit-function-declaration
+
+override c_flags = $(UAPI_CFLAGS) -Wp,-MD,$(depfile) -I$(objtree)/usr/include
+
+# The following are excluded for now because they fail to build.
+# The cause of errors are mostly missing include directives.
+# Check one by one, and send a patch to each subsystem.
+#
+# Do not add a new header to the blacklist without legitimate reason.
+# Please consider to fix the header first.
+header-test- += asm/ipcbuf.h
+header-test- += asm/msgbuf.h
+header-test- += asm/sembuf.h
+header-test- += asm/shmbuf.h
+header-test- += asm/signal.h
+header-test- += asm/ucontext.h
+header-test- += drm/vmwgfx_drm.h
+header-test- += linux/am437x-vpfe.h
+header-test- += linux/android/binderfs.h
+header-test- += linux/android/binder.h
+header-test-$(CONFIG_CPU_BIG_ENDIAN) += linux/byteorder/big_endian.h
+header-test-$(CONFIG_CPU_LITTLE_ENDIAN) += linux/byteorder/little_endian.h
+header-test- += linux/coda.h
+header-test- += linux/coda_psdev.h
+header-test- += linux/dvb/audio.h
+header-test- += linux/dvb/osd.h
+header-test- += linux/elfcore.h
+header-test- += linux/errqueue.h
+header-test- += linux/fsmap.h
+header-test- += linux/hdlc/ioctl.h
+header-test- += linux/jffs2.h
+header-test- += linux/kexec.h
+header-test- += linux/matroxfb.h
+header-test- += linux/netfilter_bridge/ebtables.h
+header-test- += linux/netfilter_ipv4/ipt_LOG.h
+header-test- += linux/netfilter_ipv6/ip6t_LOG.h
+header-test- += linux/nfc.h
+header-test- += linux/nilfs2_ondisk.h
+header-test- += linux/omap3isp.h
+header-test- += linux/omapfb.h
+header-test- += linux/patchkey.h
+header-test- += linux/phonet.h
+header-test- += linux/reiserfs_xattr.h
+header-test- += linux/scc.h
+header-test- += linux/sctp.h
+header-test- += linux/signal.h
+header-test- += linux/sysctl.h
+header-test- += linux/usb/audio.h
+header-test- += linux/ivtv.h
+header-test- += linux/v4l2-mediabus.h
+header-test- += linux/v4l2-subdev.h
+header-test- += linux/videodev2.h
+header-test- += linux/vm_sockets.h
+header-test- += misc/ocxl.h
+header-test- += mtd/mtd-abi.h
+header-test- += scsi/scsi_bsg_fc.h
+header-test- += scsi/scsi_netlink_fc.h
+header-test- += scsi/scsi_netlink.h
+header-test- += sound/asequencer.h
+header-test- += sound/asound.h
+header-test- += sound/asoc.h
+header-test- += sound/compress_offload.h
+header-test- += sound/emu10k1.h
+header-test- += sound/sfnt_info.h
+header-test- += sound/sof/eq.h
+header-test- += sound/sof/fw.h
+header-test- += sound/sof/header.h
+header-test- += sound/sof/manifest.h
+header-test- += sound/sof/trace.h
+header-test- += xen/evtchn.h
+header-test- += xen/gntdev.h
+header-test- += xen/privcmd.h
+
+# more headers are broken in some architectures
+
+ifeq ($(SRCARCH),arc)
+header-test- += linux/bpf_perf_event.h
+endif
+
+ifeq ($(SRCARCH),ia64)
+header-test- += asm/setup.h
+header-test- += asm/sigcontext.h
+header-test- += asm/perfmon.h
+header-test- += asm/perfmon_default_smpl.h
+header-test- += linux/if_bonding.h
+endif
+
+ifeq ($(SRCARCH),mips)
+header-test- += asm/stat.h
+endif
+
+ifeq ($(SRCARCH),powerpc)
+header-test- += asm/stat.h
+header-test- += linux/bpf_perf_event.h
+endif
+
+ifeq ($(SRCARCH),riscv)
+header-test- += linux/bpf_perf_event.h
+endif
+
+ifeq ($(SRCARCH),s390)
+header-test- += asm/runtime_instr.h
+header-test- += asm/zcrypt.h
+endif
+
+ifeq ($(SRCARCH),sparc)
+header-test- += asm/stat.h
+header-test- += asm/uctx.h
+header-test- += asm/fbio.h
+header-test- += asm/openpromio.h
+endif
+
+# asm-generic/*.h is used by asm/*.h, and should not be included directly
+header-test- += asm-generic/%
+
+# The rest are compile-tested
+header-test-y += $(filter-out $(header-test-), \
+			$(patsubst $(obj)/%,%, $(wildcard \
+			$(addprefix $(obj)/, *.h */*.h */*/*.h */*/*/*.h))))
+
+# For GNU Make <= 4.2.1, $(wildcard $(obj)/*/) matches to not only directories
+# but also regular files. Use $(filter %/, ...) just in case.
+clean-dirs += $(patsubst $(obj)/%/,%,$(filter %/, $(wildcard $(obj)/*/)))