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978fa00e |
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27-Mar-2024 |
Nathan Chancellor <nathan@kernel.org> |
Documentation/llvm: Note s390 LLVM=1 support with LLVM 18.1.0 and newer As of the first s390 pull request during the 6.9 merge window, commit 691632f0e869 ("Merge tag 's390-6.9-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux"), s390 can be built with LLVM=1 when using LLVM 18.1.0, which is the first version that has SystemZ support implemented in ld.lld and llvm-objcopy. Update the supported architectures table in the Kbuild LLVM documentation to note this explicitly to make it more discoverable by users and other developers. Additionally, this brings s390 in line with the rest of the architectures in the table, which all support LLVM=1. Signed-off-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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a3c6bfba |
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25-Aug-2023 |
Nick Desaulniers <ndesaulniers@google.com> |
Documentation/llvm: refresh docs Recent fixes for an embargoed hardware security vulnerability failed to link with ld.lld (LLVM's linker). [0] To be fair, our documentation mentions ``CC=clang`` foremost with ``LLVM=1`` being buried "below the fold." We want to encourage the use of ``LLVM=1`` rather than just ``CC=clang``. Make that suggestion "above the fold" and "front and center" in our docs. While here, the following additional changes were made: - remove the bit about CROSS_COMPILE setting --target=, that's no longer true. - Add ARCH=loongarch to the list of maintained targets (though we're still working on getting defconfig building cleanly at the moment; we're pretty close). - Bump ARCH=powerpc from CC=clang to LLVM=1 status. - Promote ARCH=riscv from being Maintained to being Supported. Android is working towards supporting RISC-V, and we have excellent support from multiple companies in this regard. - Note that the toolchain distribution on kernel.org has been built with profile data from kernel builds. - Note how to use ccache with clang. Link: https://github.com/ClangBuiltLinux/linux/issues/1907 [0] Reviewed-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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dcc11ac9 |
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07-Apr-2023 |
Nathan Chancellor <nathan@kernel.org> |
Documentation/llvm: Add a note about prebuilt kernel.org toolchains I recently started uploading prebuilt stable versions of LLVM to kernel.org, which should make building the kernel with LLVM more accessible to maintainers and developers. Link them in the LLVM documentation to make this more visible. Link: https://lore.kernel.org/20230319235619.GA18547@dev-arch.thelio-3990X/ Suggested-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Bill Wendling <morbo@google.com> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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0aee6bec |
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02-Feb-2023 |
Nick Desaulniers <ndesaulniers@google.com> |
Documentation/llvm: add Chimera Linux, Google and Meta datacenters Chimera Linux is a Linux distribution from 2021 that builds its kernels with Clang. Google transitioned its data center fleet to run Clang built kernels in 2021, and Meta did so as well in 2022. Meta talked about this at LPC 2022 at a talk titled Kernel Live Patching at Scale. These were important milestones for building the kernel with Clang. Making note of them helps improve confidence in the project. Reviewed-by: Tom Rix <trix@redhat.com> Reviewed-by: Nathan Chancellor <nathan@kernel.org> Reviewed-by: Sedat Dilek <sedat.dilek@gmail.com> Co-developed-by: Yonghong Song <yhs@fb.com> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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291810be |
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17-Jun-2022 |
Nick Desaulniers <ndesaulniers@google.com> |
Documentation/llvm: Update Supported Arch table While watching Michael's new talk on Clang-built-Linux, I noticed the arch table in our docs that he refers to is outdated. Add hexagon and User Mode. Bump MIPS and RISCV to LLVM=1. PowerPC is almost LLVM=1 capable; ppc64le works, but ppc64 (big endian) and ppc32 still need more work. Link: https://youtu.be/W4zdEDpvR5c?t=399 Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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e9c28192 |
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04-Mar-2022 |
Nathan Chancellor <nathan@kernel.org> |
kbuild: Make $(LLVM) more flexible The LLVM make variable allows a developer to quickly switch between the GNU and LLVM tools. However, it does not handle versioned binaries, such as the ones shipped by Debian, as LLVM=1 just defines the tool variables with the unversioned binaries. There was some discussion during the review of the patch that introduces LLVM=1 around versioned binaries, ultimately coming to the conclusion that developers can just add the folder that contains the unversioned binaries to their PATH, as Debian's versioned suffixed binaries are really just symlinks to the unversioned binaries in /usr/lib/llvm-#/bin: $ realpath /usr/bin/clang-14 /usr/lib/llvm-14/bin/clang $ PATH=/usr/lib/llvm-14/bin:$PATH make ... LLVM=1 However, that can be cumbersome to developers who are constantly testing series with different toolchains and versions. It is simple enough to support these versioned binaries directly in the Kbuild system by allowing the developer to specify the version suffix with LLVM=, which is shorter than the above suggestion: $ make ... LLVM=-14 It does not change the meaning of LLVM=1 (which will continue to use unversioned binaries) and it does not add too much additional complexity to the existing $(LLVM) code, while allowing developers to quickly test their series with different versions of the whole LLVM suite of tools. Some developers may build LLVM from source but not add the binaries to their PATH, as they may not want to use that toolchain systemwide. Support those developers by allowing them to supply the directory that the LLVM tools are available in, as it is no more complex to support than the version suffix change above. $ make ... LLVM=/path/to/llvm/ Update and reorder the documentation to reflect these new additions. At the same time, notate that LLVM=0 is not the same as just omitting it altogether, which has confused people in the past. Link: https://lore.kernel.org/r/20200317215515.226917-1-ndesaulniers@google.com/ Link: https://lore.kernel.org/r/20220224151322.072632223@infradead.org/ Suggested-by: Masahiro Yamada <masahiroy@kernel.org> Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Nathan Chancellor <nathan@kernel.org> Reviewed-by: Kees Cook <keescook@chromium.org> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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1c3493bb |
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07-Sep-2021 |
Nathan Chancellor <nathan@kernel.org> |
Documentation/llvm: update IRC location This should have been done with commit 91ed3ed0f798 ("MAINTAINERS: update ClangBuiltLinux IRC chat") but I did not realize it was in two separate spots. Link: https://lkml.kernel.org/r/20210825211823.6406-3-nathan@kernel.org Signed-off-by: Nathan Chancellor <nathan@kernel.org> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Cc: Kees Cook <keescook@chromium.org> Cc: Masahiro Yamada <masahiroy@kernel.org> Cc: Sami Tolvanen <samitolvanen@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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28f8fc19 |
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07-Sep-2021 |
Nathan Chancellor <nathan@kernel.org> |
Documentation/llvm: update mailing list We are now at llvm@lists.linux.dev. Link: https://lkml.kernel.org/r/20210825211823.6406-2-nathan@kernel.org Signed-off-by: Nathan Chancellor <nathan@kernel.org> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Cc: Kees Cook <keescook@chromium.org> Cc: Masahiro Yamada <masahiroy@kernel.org> Cc: Sami Tolvanen <samitolvanen@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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f12b034a |
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06-Aug-2021 |
Nick Desaulniers <ndesaulniers@google.com> |
scripts/Makefile.clang: default to LLVM_IAS=1 LLVM_IAS=1 controls enabling clang's integrated assembler via -integrated-as. This was an explicit opt in until we could enable assembler support in Clang for more architecures. Now we have support and CI coverage of LLVM_IAS=1 for all architecures except a few more bugs affecting s390 and powerpc. This commit flips the default from opt in via LLVM_IAS=1 to opt out via LLVM_IAS=0. CI systems or developers that were previously doing builds with CC=clang or LLVM=1 without explicitly setting LLVM_IAS must now explicitly opt out via LLVM_IAS=0, otherwise they will be implicitly opted-in. This finally shortens the command line invocation when cross compiling with LLVM to simply: $ make ARCH=arm64 LLVM=1 Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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e08831ba |
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02-Aug-2021 |
Nick Desaulniers <ndesaulniers@google.com> |
Documentation/llvm: update CROSS_COMPILE inferencing As noted by Masahiro, document how we can generally infer CROSS_COMPILE (and the more specific details about --target and --prefix) based on ARCH. Change use of env vars to command line parameters. Suggested-by: Masahiro Yamada <masahiroy@kernel.org> Reviewed-by: Fangrui Song <maskray@google.com> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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ed4e9e61 |
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13-Jan-2021 |
Nathan Chancellor <nathan@kernel.org> |
Documentation/llvm: Add a section about supported architectures The most common question around building the Linux kernel with clang is "does it work?" and the answer has always been "it depends on your architecture, configuration, and LLVM version" with no hard answers for users wanting to experiment. LLVM support has significantly improved over the past couple of years, resulting in more architectures and configurations supported, and continuous integration has made it easier to see what works and what does not. Add a section that goes over what architectures are supported in the current kernel version, how they should be built (with just clang or the LLVM utilities as well), and the level of support they receive. This will make it easier for people to try out building their kernel with LLVM and reporting issues that come about from it. Suggested-by: Miguel Ojeda <ojeda@kernel.org> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> Reviewed-by: Nick Desaulniers <ndesaulnier@google.com> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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d9b5665f |
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23-Oct-2020 |
Vasily Gorbik <gor@linux.ibm.com> |
kbuild: remove unused OBJSIZE The "size" tool has been solely used by s390 to enforce .bss section usage restrictions in early startup code. Since commit 980d5f9ab36b ("s390/boot: enable .bss section for compressed kernel") and commit 2e83e0eb85ca ("s390: clean .bss before running uncompressed kernel") these restrictions have been lifted for the decompressor and uncompressed kernel and the size tool is now unused. Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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e30d694c |
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25-Sep-2020 |
Florian Fainelli <f.fainelli@gmail.com> |
Documentation/llvm: Fix clang target examples clang --target=<triple> is how we can specify a particular toolchain triple to be use, fix the two occurences in the documentation. Fixes: fcf1b6a35c16 ("Documentation/llvm: add documentation on building w/ Clang/LLVM") Signed-off-by: Florian Fainelli <f.fainelli@gmail.com> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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3519c4d6 |
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26-Aug-2020 |
Nick Desaulniers <ndesaulniers@google.com> |
Documentation: add minimum clang/llvm version Based on a vote at the LLVM BoF at Plumbers 2020, we decided to start small, supporting just one formal upstream release of LLVM for now. We can probably widen the support window of supported versions over time. Also, note that LLVM's release process is different than GCC's. GCC tends to have 1 major release per year while releasing minor updates to the past 3 major versions. LLVM tends to support one major release and one minor release every six months. Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> Tested-by: Gustavo A. R. Silva <gustavoars@kernel.org> Tested-by: Nathan Chancellor <natechancellor@gmail.com> Reviewed-by: Kees Cook <keescook@chromium.org> Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> Reviewed-by: Masahiro Yamada <masahiroy@kernel.org> Acked-by: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20200826191555.3350406-1-ndesaulniers@google.com Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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91a9d502 |
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25-Aug-2020 |
Nathan Chancellor <nathan@kernel.org> |
Documentation/llvm: Improve formatting of commands, variables, and arguments While reviewing a separate patch, I noticed that the formatting of the commands, variables, and arguments was not in a monospaced font like the rest of the Kbuild documentation (see kbuild/kconfig.rst for an example). This is due to a lack of "::" before indented command blocks and single backticks instead of double backticks for inline formatting. Add those so that the document looks nicer in an HTML format, while not ruining the look in plain text. As a result of this, we can remove the escaped backslashes in the last code block and move them to single backslashes. Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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16a122c7 |
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19-Jul-2020 |
Alexander A. Klimov <grandmaster@al2klimov.de> |
kbuild: Replace HTTP links with HTTPS ones Rationale: Reduces attack surface on kernel devs opening the links for MITM as HTTPS traffic is much harder to manipulate. Deterministic algorithm: For each file: If not .svg: For each line: If doesn't contain `\bxmlns\b`: For each link, `\bhttp://[^# \t\r\n]*(?:\w|/)`: If neither `\bgnu\.org/license`, nor `\bmozilla\.org/MPL\b`: If both the HTTP and HTTPS versions return 200 OK and serve the same content: Replace HTTP with HTTPS. Signed-off-by: Alexander A. Klimov <grandmaster@al2klimov.de> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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a0d1c951 |
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07-Apr-2020 |
Masahiro Yamada <masahiroy@kernel.org> |
kbuild: support LLVM=1 to switch the default tools to Clang/LLVM As Documentation/kbuild/llvm.rst implies, building the kernel with a full set of LLVM tools gets very verbose and unwieldy. Provide a single switch LLVM=1 to use Clang and LLVM tools instead of GCC and Binutils. You can pass it from the command line or as an environment variable. Please note LLVM=1 does not turn on the integrated assembler. You need to pass LLVM_IAS=1 to use it. When the upstream kernel is ready for the integrated assembler, I think we can make it default. We discussed what we need, and we agreed to go with a simple boolean flag that switches both target and host tools: https://lkml.org/lkml/2020/3/28/494 https://lkml.org/lkml/2020/4/3/43 Some items discussed, but not adopted: - LLVM_DIR When multiple versions of LLVM are installed, I just thought supporting LLVM_DIR=/path/to/my/llvm/bin/ might be useful. CC = $(LLVM_DIR)clang LD = $(LLVM_DIR)ld.lld ... However, we can handle this by modifying PATH. So, we decided to not do this. - LLVM_SUFFIX Some distributions (e.g. Debian) package specific versions of LLVM with naming conventions that use the version as a suffix. CC = clang$(LLVM_SUFFIX) LD = ld.lld(LLVM_SUFFIX) ... will allow a user to pass LLVM_SUFFIX=-11 to use clang-11 etc., but the suffixed versions in /usr/bin/ are symlinks to binaries in /usr/lib/llvm-#/bin/, so this can also be handled by PATH. Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> Tested-by: Nathan Chancellor <natechancellor@gmail.com> # build Tested-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
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7e20e47c |
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07-Apr-2020 |
Masahiro Yamada <masahiroy@kernel.org> |
kbuild: replace AS=clang with LLVM_IAS=1 The 'AS' variable is unused for building the kernel. Only the remaining usage is to turn on the integrated assembler. A boolean flag is a better fit for this purpose. AS=clang was added for experts. So, I replaced it with LLVM_IAS=1, breaking the backward compatibility. Suggested-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
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0f44fbc1 |
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02-Apr-2020 |
Fangrui Song <maskray@google.com> |
Documentation/llvm: fix the name of llvm-size The tool is called llvm-size, not llvm-objsize. Fixes: fcf1b6a35c16 ("Documentation/llvm: add documentation on building w/ Clang/LLVM") Signed-off-by: Fangrui Song <maskray@google.com> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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fcf1b6a3 |
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26-Feb-2020 |
Nick Desaulniers <ndesaulniers@google.com> |
Documentation/llvm: add documentation on building w/ Clang/LLVM Added to kbuild documentation. Provides more official info on building kernels with Clang and LLVM than our wiki. Suggested-by: Kees Cook <keescook@chromium.org> Reviewed-by: Kees Cook <keescook@chromium.org> Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> Reviewed-by: Sedat Dilek <sedat.dilek@gmail.com> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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