clang compile error with latest kernel

[Chung Chung]

Hi, I am wondering if anyone has successfully compiled latest kernel using clang, I have
been having problem with it for the last few month, 
and here is the error that I have:

In file included from drivers/tty/tty_io.c:103:
./include/linux/termios_internal.h:37:5: error: conflicting types for
'user_termio_to_kernel_termios'
int user_termio_to_kernel_termios(struct ktermios *, struct termio __user *);
    ^
./include/asm-generic/termios.h:20:19: note: previous definition is here
static inline int user_termio_to_kernel_termios(struct ktermios *termios,

Sorry, if it has been discussed before, but I don't seem to find the answer.

Chung

[stan]

On Thu, 16 Feb 2023 17:18:36 -0000
"Chung Chung" <ctwo0002(a)gmail.com&gt; wrote:

>  Hi, I am wondering if anyone has successfully compiled latest kernel
>  using clang, I have been having problem with it for the last few
>  month, and here is the error that I have:
>  
>  In file included from drivers/tty/tty_io.c:103:
>  ./include/linux/termios_internal.h:37:5: error: conflicting types for
>  'user_termio_to_kernel_termios' int
>  user_termio_to_kernel_termios(struct ktermios *, struct termio __user
>  *); ^ ./include/asm-generic/termios.h:20:19: note: previous
>  definition is here static inline int
>  user_termio_to_kernel_termios(struct ktermios *termios,
>  
>  Sorry, if it has been discussed before, but I don't seem to find the
>  answer. 
That looks like a bug.  I compile the kernel, but it uses the default
compiler, and I think that is gcc, so it compiles fine.  I would
suggest you file a bug against the kernel at
https://bugzilla.redhat.com/
There are no current bugs about this in the fedora bugzilla
or 
put a message on the fedora kernel list asking about the problem, with
the above information.
kernel(a)lists.fedoraproject.org

I *think* that gcc considers static inline to be a suggestion, while
clang is probably considering it required.  Might be just the
compiler flags.  Could be wrong.

[Barry]

>  On 16 Feb 2023, at 17:18, Chung Chung <ctwo0002(a)gmail.com&gt;
> wrote:
>  
>  
>  Hi, I am wondering if anyone has successfully compiled latest kernel using clang, I have
> been having problem with it for the last few month, 
>  and here is the error that I have:
>  
>  In file included from drivers/tty/tty_io.c:103:
>  ./include/linux/termios_internal.h:37:5: error: conflicting types for
> 'user_termio_to_kernel_termios'
>  int user_termio_to_kernel_termios(struct ktermios *, struct termio __user *);
>     ^
>  ./include/asm-generic/termios.h:20:19: note: previous definition is here
>  static inline int user_termio_to_kernel_termios(struct ktermios *termios,
>  
>  Sorry, if it has been discussed before, but I don't seem to find the answer. 
I am not sure if clang, llvm, is supported for the linux kernel.
Maybe someone else here can comment.

I do know that there are people working on getting it working.

Using gcc will work as that is supported.

Barry
>  
>  Chung
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[Jeffrey Walton]

On Thu, Feb 16, 2023 at 1:02 PM Barry <barry(a)barrys-emacs.org&gt; wrote:
>  > On 16 Feb 2023, at 17:18, Chung Chung <ctwo0002(a)gmail.com&gt; wrote:
>  >
>  > Hi, I am wondering if anyone has successfully compiled latest kernel using clang, I
> have been having problem with it for the last few month,
>  > and here is the error that I have:
>  >
>  > In file included from drivers/tty/tty_io.c:103:
>  > ./include/linux/termios_internal.h:37:5: error: conflicting types for
> 'user_termio_to_kernel_termios'
>  > int user_termio_to_kernel_termios(struct ktermios *, struct termio __user *);
>  >    ^
>  > ./include/asm-generic/termios.h:20:19: note: previous definition is here
>  > static inline int user_termio_to_kernel_termios(struct ktermios *termios,
>  >
>  > Sorry, if it has been discussed before, but I don't seem to find the answer.
>
>  I am not sure if clang, llvm, is supported for the linux kernel.
>  Maybe someone else here can comment.
>
>  I do know that there are people working on getting it working.
>
>  Using gcc will work as that is supported. 
I think the LLVM devs presented results of compiling the kernel
several years ago. I don't recall the link to the talk, though.

I think some of the kernel devs are the biggest problem. Some of the
developers feel GCC is the only compiler to support. They rely on
GCC-isms, and don't care about things like undefined behavior since it
"works for me using GCC." I've even had some of the devs tell me they
don't care about the C standard. That was very befuddling to me.

Jeff

[Barry Scott]

>  On 16 Feb 2023, at 18:42, Jeffrey Walton <noloader(a)gmail.com&gt;
> wrote:
>  
>  I think some of the kernel devs are the biggest problem. Some of the
>  developers feel GCC is the only compiler to support. They rely on
>  GCC-isms, and don't care about things like undefined behavior since it
>  "works for me using GCC." I've even had some of the devs tell me they
>  don't care about the C standard. That was very befuddling to me. 
The problem is that LLVM has different undefined behaviour from GCC. That has to be
understood and coded around. You cannot write an OS or device driver based on the
C standard's memory model. Linux has its own definition of a memory-model that any
compiler must be able to implement to write a kernel.

There are articles on lwn.net that talk to these issues.

Try a search for "lwn bad compiler" to find https://lwn.net/Articles/799218/
and others that talk about why this is not what you are suggesting.

Barry

[Michael Hennebry]

On Sat, 18 Feb 2023, Barry Scott wrote:

> > On 16 Feb 2023, at 18:42, Jeffrey Walton <noloader(a)gmail.com&gt; wrote:
> >
> > I think some of the kernel devs are the biggest problem. Some of the
> > developers feel GCC is the only compiler to support. They rely on
> > GCC-isms, and don't care about things like undefined behavior since it
> > "works for me using GCC." I've even had some of the devs tell me they
> > don't care about the C standard. That was very befuddling to me.
>
>  The problem is that LLVM has different undefined behaviour from GCC. That has to be
That might be a problem, but it is not the current problem.
In the case at hand, clang will not compile the kernel code at all.
A slight editing of a header file should cure that particular problem.

>  understood and coded around. You cannot write an OS or device driver
> based on the
>  C standard's memory model. Linux has its own definition of a memory-model that any
>  compiler must be able to implement to write a kernel. 
volatile would help here.
It limits allowed optimizations.
Also, C does have a limit on how one can
convert between integers and pointers.
The result is supposed to be unsurprising
to one familiar with the architecture.

When things get bad enough,
that is why Odin invented inline assembly.

-- 
Michael   hennebry(a)mail.cs.ndsu.NoDak.edu
"Occasionally irrational explanations are required"  --  Luke Roman

[Jeffrey Walton]

On Thu, Feb 16, 2023 at 12:18 PM Chung Chung <ctwo0002(a)gmail.com&gt; wrote:
>  Hi, I am wondering if anyone has successfully compiled latest kernel using clang, 
I have not tried to build a kernel with Clang. However the LLVM devs
have done it in the past.

Also see https://docs.kernel.org/kbuild/llvm.html . There are helpful
links at the bottom of the page.

>  I have been having problem with it for the last few month,
>  and here is the error that I have:
>
>  In file included from drivers/tty/tty_io.c:103:
>  ./include/linux/termios_internal.h:37:5: error: conflicting types for
> 'user_termio_to_kernel_termios'
>  int user_termio_to_kernel_termios(struct ktermios *, struct termio __user *);
>      ^
>  ./include/asm-generic/termios.h:20:19: note: previous definition is here
>  static inline int user_termio_to_kernel_termios(struct ktermios *termios, 
It does not look like this issue has been reported in the LLVM kernel
issue tracker at https://github.com/ClangBuiltLinux/linux/issues .

Jeff

[Michael Hennebry]

On Thu, 16 Feb 2023, Chung Chung wrote:

>  Hi, I am wondering if anyone has successfully compiled latest kernel
> using clang, I have been having problem with it for the last few month,
>  and here is the error that I have:
>
>  In file included from drivers/tty/tty_io.c:103:
>  ./include/linux/termios_internal.h:37:5: error: conflicting types for
> 'user_termio_to_kernel_termios'
>  int user_termio_to_kernel_termios(struct ktermios *, struct termio __user *);
>     ^
>  ./include/asm-generic/termios.h:20:19: note: previous definition is here
>  static inline int user_termio_to_kernel_termios(struct ktermios *termios, 
Not enough is shown to be sure, but I think the problem is that a function
is declared external not inline before being defined as static inline.
My guess is that gcc accepts that without comment, even though it should not,
and clang rejects it with a not-so-great error message.

-- 
Michael   hennebry(a)mail.cs.ndsu.NoDak.edu
"Occasionally irrational explanations are required"  --  Luke Roman

[Chung Chung]

Thank you for all the suggestions.  I am going to try a few and let you guys know.
Thanks again!!!

Chung