[v2] Documentation/llvm: add documentation on building w/ Clang/LLVM

Commit Message

Nick Desaulniers Feb. 25, 2020, 9:02 p.m. UTC

Added to kbuild documentation. Provides more official info on building
kernels with Clang and LLVM than our wiki.

Suggested-by: Randy Dunlap <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Reviewed-by: Nathan Chancellor <[e-mail]>
Reviewed-by: Sedat Dilek <[e-mail]>
Signed-off-by: Nick Desaulniers <[e-mail]>
---
Changes V1 -> V2:
* s/On going/ongoing/
* add Randy's Suggested-by
* add Nathan and Sedat's Reviewed-by
* Upgrade Kees' Sugguested-by to Reviewed-by
* s/suffix/prefix/


 Documentation/kbuild/index.rst |  1 +
 Documentation/kbuild/llvm.rst  | 80 ++++++++++++++++++++++++++++++++++
 2 files changed, 81 insertions(+)
 create mode 100644 Documentation/kbuild/llvm.rst

Comments

Masahiro Yamada Feb. 26, 2020, 11:30 a.m. UTC | #1

Hi.


On Wed, Feb 26, 2020 at 6:02 AM Nick Desaulniers
<[e-mail]> wrote:
>
> Added to kbuild documentation. Provides more official info on building
> kernels with Clang and LLVM than our wiki.
>
> Suggested-by: Randy Dunlap <[e-mail]>
> Reviewed-by: Kees Cook <[e-mail]>
> Reviewed-by: Nathan Chancellor <[e-mail]>
> Reviewed-by: Sedat Dilek <[e-mail]>
> Signed-off-by: Nick Desaulniers <[e-mail]>
> ---
> Changes V1 -> V2:
> * s/On going/ongoing/
> * add Randy's Suggested-by


I do not understand this tag update.

As far as I saw the review process,
I do not think Randy deserves to have Suggested-by
because he just pointed out a typo (on going -> ongoing) :
https://patchwork.kernel.org/patch/11401189/#23179575

(or, was there off-line activity I had missed?)


> * add Nathan and Sedat's Reviewed-by
> * Upgrade Kees' Sugguested-by to Reviewed-by

We can add both

Suggested-by: Kees Cook <[e-mail]>

and

Reviewed-by: Kees Cook <[e-mail]>



I think Suggested-by and Reviewed-by should be orthogonal.


Thanks.






> * s/suffix/prefix/
>
>
>  Documentation/kbuild/index.rst |  1 +
>  Documentation/kbuild/llvm.rst  | 80 ++++++++++++++++++++++++++++++++++
>  2 files changed, 81 insertions(+)
>  create mode 100644 Documentation/kbuild/llvm.rst
>
> diff --git a/Documentation/kbuild/index.rst b/Documentation/kbuild/index.rst
> index 0f144fad99a6..3882bd5f7728 100644
> --- a/Documentation/kbuild/index.rst
> +++ b/Documentation/kbuild/index.rst
> @@ -19,6 +19,7 @@ Kernel Build System
>
>      issues
>      reproducible-builds
> +    llvm
>
>  .. only::  subproject and html
>
> diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
> new file mode 100644
> index 000000000000..d6c79eb4e23e
> --- /dev/null
> +++ b/Documentation/kbuild/llvm.rst
> @@ -0,0 +1,80 @@
> +==============================
> +Building Linux with Clang/LLVM
> +==============================
> +
> +This document covers how to build the Linux kernel with Clang and LLVM
> +utilities.
> +
> +About
> +-----
> +
> +The Linux kernel has always traditionally been compiled with GNU toolchains
> +such as GCC and binutils. Ongoing work has allowed for `Clang
> +<https://clang.llvm.org/>`_ and `LLVM <https://llvm.org/>`_ utilities to be
> +used as viable substitutes. Distributions such as `Android
> +<https://www.android.com/>`_, `ChromeOS
> +<https://www.chromium.org/chromium-os>`_, and `OpenMandriva
> +<https://www.openmandriva.org/>`_ use Clang built kernels.  `LLVM is a
> +collection of toolchain components implemented in terms of C++ objects
> +<https://www.aosabook.org/en/llvm.html>`_. Clang is a front-end to LLVM that
> +supports C and the GNU C extensions required by the kernel, and is pronounced
> +"klang," not "see-lang."
> +
> +Clang
> +-----
> +
> +The compiler used can be swapped out via `CC=` command line argument to `make`.
> +`CC=` should be set when selecting a config and during a build.
> +
> +       make CC=clang defconfig
> +
> +       make CC=clang
> +
> +Cross Compiling
> +---------------
> +
> +A single Clang compiler binary will typically contain all supported backends,
> +which can help simplify cross compiling.
> +
> +       ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang
> +
> +`CROSS_COMPILE` is not used to prefix the Clang compiler binary, instead
> +`CROSS_COMPILE` is used to set a command line flag: `--target <triple>`. For
> +example:
> +
> +       clang --target aarch64-linux-gnu foo.c
> +
> +LLVM Utilities
> +--------------
> +
> +LLVM has substitutes for GNU binutils utilities. These can be invoked as
> +additional parameters to `make`.
> +
> +       make CC=clang AS=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \\
> +         OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump OBJSIZE=llvm-objsize \\
> +         READELF=llvm-readelf HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar \\
> +         HOSTLD=ld.lld
> +
> +Getting Help
> +------------
> +
> +- `Website <https://clangbuiltlinux.github.io/>`_
> +- `Mailing List <https://groups.google.com/forum/#!forum/clang-built-linux>`_: <[e-mail]>
> +- `Issue Tracker <https://github.com/ClangBuiltLinux/linux/issues>`_
> +- IRC: #clangbuiltlinux on chat.freenode.net
> +- `Telegram <https://t.me/ClangBuiltLinux>`_: @ClangBuiltLinux
> +- `Wiki <https://github.com/ClangBuiltLinux/linux/wiki>`_
> +- `Beginner Bugs <https://github.com/ClangBuiltLinux/linux/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22>`_
> +
> +Getting LLVM
> +-------------
> +
> +- http://releases.llvm.org/download.html
> +- https://github.com/llvm/llvm-project
> +- https://llvm.org/docs/GettingStarted.html
> +- https://llvm.org/docs/CMake.html
> +- https://apt.llvm.org/
> +- https://www.archlinux.org/packages/extra/x86_64/llvm/
> +- https://github.com/ClangBuiltLinux/tc-build
> +- https://github.com/ClangBuiltLinux/linux/wiki/Building-Clang-from-source
> +- https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/
> --
> 2.25.0.265.gbab2e86ba0-goog
>


--
Best Regards
Masahiro Yamada

Sedat Dilek Feb. 26, 2020, 12:29 p.m. UTC | #2

On Wed, Feb 26, 2020 at 12:31 PM Masahiro Yamada <[e-mail]> wrote:
>
> Hi.
>
>
> On Wed, Feb 26, 2020 at 6:02 AM Nick Desaulniers
> <[e-mail]> wrote:
> >
> > Added to kbuild documentation. Provides more official info on building
> > kernels with Clang and LLVM than our wiki.
> >
> > Suggested-by: Randy Dunlap <[e-mail]>
> > Reviewed-by: Kees Cook <[e-mail]>
> > Reviewed-by: Nathan Chancellor <[e-mail]>
> > Reviewed-by: Sedat Dilek <[e-mail]>
> > Signed-off-by: Nick Desaulniers <[e-mail]>
> > ---
> > Changes V1 -> V2:
> > * s/On going/ongoing/
> > * add Randy's Suggested-by
>
>
> I do not understand this tag update.
>
> As far as I saw the review process,
> I do not think Randy deserves to have Suggested-by
> because he just pointed out a typo (on going -> ongoing) :
> https://patchwork.kernel.org/patch/11401189/#23179575
>
> (or, was there off-line activity I had missed?)
>

Hi Masahiro,

I got some credits from Nick for a review by seeing a typo - not on a
review of the code - and H. Peter Anvin asked why.

I am not sure what is here the correct credit to give.
Depends a "Reviewed-by" and/or "Suggested-by" on a technical review?

My POV: When people take time to look over patches they should get
credits - sort of esteem.

Regards,
- Sedat -

P.S.: Tipp: Use codespell to find typos :-).

[1] https://git.kernel.org/linus/0e2e160033283e20f688d8bad5b89460cc5bfcc4
"x86/asm: Add _ASM_ARG* constants for argument registers to <asm/asm.h>"

Masahiro Yamada Feb. 26, 2020, 12:38 p.m. UTC | #3

On Wed, Feb 26, 2020 at 9:26 PM Sedat Dilek <[e-mail]> wrote:
>
> On Wed, Feb 26, 2020 at 12:31 PM Masahiro Yamada <[e-mail]> wrote:
> >
> > Hi.
> >
> >
> > On Wed, Feb 26, 2020 at 6:02 AM Nick Desaulniers
> > <[e-mail]> wrote:
> > >
> > > Added to kbuild documentation. Provides more official info on building
> > > kernels with Clang and LLVM than our wiki.
> > >
> > > Suggested-by: Randy Dunlap <[e-mail]>
> > > Reviewed-by: Kees Cook <[e-mail]>
> > > Reviewed-by: Nathan Chancellor <[e-mail]>
> > > Reviewed-by: Sedat Dilek <[e-mail]>
> > > Signed-off-by: Nick Desaulniers <[e-mail]>
> > > ---
> > > Changes V1 -> V2:
> > > * s/On going/ongoing/
> > > * add Randy's Suggested-by
> >
> >
> > I do not understand this tag update.
> >
> > As far as I saw the review process,
> > I do not think Randy deserves to have Suggested-by
> > because he just pointed out a typo (on going -> ongoing) :
> > https://patchwork.kernel.org/patch/11401189/#23179575
> >
> > (or, was there off-line activity I had missed?)
> >
>
> Hi Masahiro,
>
> I got some credits from Nick for a review by seeing a typo - not on a
> review of the code - and H. Peter Anvin asked why.
>
> I am not sure what is here the correct credit to give.
> Depends a "Reviewed-by" and/or "Suggested-by" on a technical review?



Documentation/process/submitting-patches.rst

  13) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:

is a helpful guideline.

Sedat Dilek Feb. 26, 2020, 1:02 p.m. UTC | #4

On Wed, Feb 26, 2020 at 1:39 PM Masahiro Yamada <[e-mail]> wrote:
>
> On Wed, Feb 26, 2020 at 9:26 PM Sedat Dilek <[e-mail]> wrote:
> >
> > On Wed, Feb 26, 2020 at 12:31 PM Masahiro Yamada <[e-mail]> wrote:
> > >
> > > Hi.
> > >
> > >
> > > On Wed, Feb 26, 2020 at 6:02 AM Nick Desaulniers
> > > <[e-mail]> wrote:
> > > >
> > > > Added to kbuild documentation. Provides more official info on building
> > > > kernels with Clang and LLVM than our wiki.
> > > >
> > > > Suggested-by: Randy Dunlap <[e-mail]>
> > > > Reviewed-by: Kees Cook <[e-mail]>
> > > > Reviewed-by: Nathan Chancellor <[e-mail]>
> > > > Reviewed-by: Sedat Dilek <[e-mail]>
> > > > Signed-off-by: Nick Desaulniers <[e-mail]>
> > > > ---
> > > > Changes V1 -> V2:
> > > > * s/On going/ongoing/
> > > > * add Randy's Suggested-by
> > >
> > >
> > > I do not understand this tag update.
> > >
> > > As far as I saw the review process,
> > > I do not think Randy deserves to have Suggested-by
> > > because he just pointed out a typo (on going -> ongoing) :
> > > https://patchwork.kernel.org/patch/11401189/#23179575
> > >
> > > (or, was there off-line activity I had missed?)
> > >
> >
> > Hi Masahiro,
> >
> > I got some credits from Nick for a review by seeing a typo - not on a
> > review of the code - and H. Peter Anvin asked why.
> >
> > I am not sure what is here the correct credit to give.
> > Depends a "Reviewed-by" and/or "Suggested-by" on a technical review?
>
>
>
> Documentation/process/submitting-patches.rst
>
>   13) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
>
> is a helpful guideline.
>

Thanks for CCing Randy and the pointer to
"Documentation/process/submitting-patches.rst" file.

This document [1] is mostly focusing on technical handling.

- Sedat -

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst#n584

Randy Dunlap Feb. 26, 2020, 3:45 p.m. UTC | #5

On 2/26/20 3:30 AM, Masahiro Yamada wrote:
> Hi.
> 
> 
> On Wed, Feb 26, 2020 at 6:02 AM Nick Desaulniers
> <[e-mail]> wrote:
>>
>> Added to kbuild documentation. Provides more official info on building
>> kernels with Clang and LLVM than our wiki.
>>
>> Suggested-by: Randy Dunlap <[e-mail]>
>> Reviewed-by: Kees Cook <[e-mail]>
>> Reviewed-by: Nathan Chancellor <[e-mail]>
>> Reviewed-by: Sedat Dilek <[e-mail]>
>> Signed-off-by: Nick Desaulniers <[e-mail]>
>> ---
>> Changes V1 -> V2:
>> * s/On going/ongoing/
>> * add Randy's Suggested-by
> 
> 
> I do not understand this tag update.
> 
> As far as I saw the review process,
> I do not think Randy deserves to have Suggested-by
> because he just pointed out a typo (on going -> ongoing) :

I agree.

> https://patchwork.kernel.org/patch/11401189/#23179575
> 
> (or, was there off-line activity I had missed?)

Patch

diff --git a/Documentation/kbuild/index.rst b/Documentation/kbuild/index.rst
index 0f144fad99a6..3882bd5f7728 100644
--- a/Documentation/kbuild/index.rst
+++ b/Documentation/kbuild/index.rst
@@ -19,6 +19,7 @@  Kernel Build System
 
     issues
     reproducible-builds
+    llvm
 
 .. only::  subproject and html
 
diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
new file mode 100644
index 000000000000..d6c79eb4e23e
--- /dev/null
+++ b/Documentation/kbuild/llvm.rst
@@ -0,0 +1,80 @@ 
+==============================
+Building Linux with Clang/LLVM
+==============================
+
+This document covers how to build the Linux kernel with Clang and LLVM
+utilities.
+
+About
+-----
+
+The Linux kernel has always traditionally been compiled with GNU toolchains
+such as GCC and binutils. Ongoing work has allowed for `Clang
+<https://clang.llvm.org/>`_ and `LLVM <https://llvm.org/>`_ utilities to be
+used as viable substitutes. Distributions such as `Android
+<https://www.android.com/>`_, `ChromeOS
+<https://www.chromium.org/chromium-os>`_, and `OpenMandriva
+<https://www.openmandriva.org/>`_ use Clang built kernels.  `LLVM is a
+collection of toolchain components implemented in terms of C++ objects
+<https://www.aosabook.org/en/llvm.html>`_. Clang is a front-end to LLVM that
+supports C and the GNU C extensions required by the kernel, and is pronounced
+"klang," not "see-lang."
+
+Clang
+-----
+
+The compiler used can be swapped out via `CC=` command line argument to `make`.
+`CC=` should be set when selecting a config and during a build.
+
+	make CC=clang defconfig
+
+	make CC=clang
+
+Cross Compiling
+---------------
+
+A single Clang compiler binary will typically contain all supported backends,
+which can help simplify cross compiling.
+
+	ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang
+
+`CROSS_COMPILE` is not used to prefix the Clang compiler binary, instead
+`CROSS_COMPILE` is used to set a command line flag: `--target <triple>`. For
+example:
+
+	clang --target aarch64-linux-gnu foo.c
+
+LLVM Utilities
+--------------
+
+LLVM has substitutes for GNU binutils utilities. These can be invoked as
+additional parameters to `make`.
+
+	make CC=clang AS=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \\
+	  OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump OBJSIZE=llvm-objsize \\
+	  READELF=llvm-readelf HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar \\
+	  HOSTLD=ld.lld
+
+Getting Help
+------------
+
+- `Website <https://clangbuiltlinux.github.io/>`_
+- `Mailing List <https://groups.google.com/forum/#!forum/clang-built-linux>`_: <[e-mail]>
+- `Issue Tracker <https://github.com/ClangBuiltLinux/linux/issues>`_
+- IRC: #clangbuiltlinux on chat.freenode.net
+- `Telegram <https://t.me/ClangBuiltLinux>`_: @ClangBuiltLinux
+- `Wiki <https://github.com/ClangBuiltLinux/linux/wiki>`_
+- `Beginner Bugs <https://github.com/ClangBuiltLinux/linux/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22>`_
+
+Getting LLVM
+-------------
+
+- http://releases.llvm.org/download.html
+- https://github.com/llvm/llvm-project
+- https://llvm.org/docs/GettingStarted.html
+- https://llvm.org/docs/CMake.html
+- https://apt.llvm.org/
+- https://www.archlinux.org/packages/extra/x86_64/llvm/
+- https://github.com/ClangBuiltLinux/tc-build
+- https://github.com/ClangBuiltLinux/linux/wiki/Building-Clang-from-source
+- https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/