On Fri, Jun 28, 2019 at 1:40 AM Masahiro Yamada
[off-list ref] 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.


-- 
Best Regards
Masahiro Yamada