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Subject: Re: uapi headers userspace build results
To:     Randy Dunlap <rdunlap@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>
Cc:     linux-kbuild <linux-kbuild@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        kernel-team@android.com
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 <1ef3a7b9-5172-9f7a-01fa-4866e765fbbe@google.com>
 <b5a73c3f-b70d-110f-896d-82fd81982cf8@infradead.org>
From:   Jayant Chowdhary <jchowdhary@google.com>
Message-ID: <8a36d3ba-977b-49ca-c431-90ef53071f88@google.com>
Date:   Mon, 18 Jun 2018 18:47:03 -0700
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Hi Randy,

On 06/12/2018 05:07 PM, Randy Dunlap wrote:
> On 06/12/2018 01:39 PM, Jayant Chowdhary wrote:
>> Hi Randy,
>>
>> On 06/11/2018 10:49 PM, Randy Dunlap wrote:
>>> Hi,
>>>
>>> Here is what I have so far.  It begins with a makefile and some
>>> template files that are added to.  There's a good bit of Perl also.
>>>
>>> I put all of these files in tools/uapi/ and run them from there.
>>>
>>> There is one .c file generated for each .h file in builddir/usr/include
>>> (O=builddir).
>>>
>>
>> Thanks for this! I wrote a small Makefile (uapi-compile.mk) which I'd put in
>> tools/build (I can change this to tools/uapi, if that is more apt).
> 
> Your makefile foo is much better than mine is.
> Yes, I think that it deserves to be in its own sub-directory.
> 
>> uapi-compile.mk straight-away compiles the uapi headers, without pulling them
>> into any generated c source files. It may also be invoked with an environment
> 
> Hm, I didn't even know that is possible.
> 
>> variable 'UAPI_DIR' specifying the directory, for which the user would like to
>> compile headers. This way we can test a directory at a time as well. In your
> 
> Yes, good, I was planning to make a way to restrict the build to certain sub-dirs.
> 
>> opinion, would this be simpler to have rather than having to auto-generate c
>> source files including each uapi header and also autog-enerating the make
>> targets? I feel like this approach would make maintaining these makefiles/
>> scripts easier as well.
> 
> Sure, this is much better than my scripts.
> 
>>> Out of 889 header files, I see 45 errors.  That is better than I expected.
>>>
>>> The makefiles and scripts are attached (tar), as well as the output (I used
>>> 'make -ik' so that make would keep going after errors and attempt to build
>>> all target files).
>>>
>>> have fun!
>>>
>>
>> I did a 'make ARCH=arm64 headers_install' from the kernel source's root, and
>> then a 'make -kf uapi-compile.mk all > build.log 2>&1' to compile all the
>> headers. Out of 864 headers, I see 20 compilation failures.
>>
>> I'm attaching uapi-compile.mk and the build.log file along.
> 
> I have some usage comments.
> 
> Since I ran 'make ARCH=x86_64 O=xx64 headers_install', I had to modify
> uapi-compile.mk to use that SRC_DIR:
> 
> SRC_DIR :=../../xx64
> 
> Also, I first tried to make BDIR as a sub-directory of tools/uapi/ and
> uapi-compile.mk did not work (when using BDIR=BDIR).
> Then I did 'mkdir ../../xx64/BDIR' and specified BDIR=../../xx64/BDIR and
> that worked.  But:  that sub-dir is not used:
> 
> gcc -I../../xx64/usr/include/ --include=../../xx64/usr/include/linux/posix_types.h --include=../../xx64/usr/include/asm-generic/ipcbuf.h --include=stdarg.h --include=stdint.h --include=stddef.h -c ../../xx64/usr/include//linux/caif/caif_socket.h -o ../../xx64/BDIR/../../xx64/usr/include//linux/caif/caif_socket.o
> [see the next comment]
> 
> Oh, this makefile builds the .o files in the same sub-dirs as their
> respective .h files.  I don't especially like that, but as long as
> make clean works, it will do.  [and make clean does work]
> 

Thanks for these comments. I'll take care of them in my patch-set. I've got a
couple of questions for you. Since most of the errors were found in the
include/uapi/linux directory, I tried investigating why.

1) I found that multiple headers depend on the definition of types such as
pid_t, which have no definition in the set of uapi headers. There is a
definition (of pid_t) in include/linux/types.h, and I thought we could try
exposing that in the set of uapi headers. One problem I can see with that is
that the header has some definitions which depend on kernel configs: eg:
CONFIG_ARCH_DMA_ADDR_T_64BIT. Since user-land programs shouldn't really assume
kernel configs, I was thinking we should re-factor this header so that
appropriate parts can be exposed to user-land.

2) Some headers try to expose information which should probably not be exposed
to user-land. eg: wait_queue_head in linux/coda_psdev.h (this header should
probably be removed altogether ?)

Do you have better ideas ?

Thanks,
Jayant

> Thanks.
>