linux.git/Documentation/kbuild, branch v6.0

asm goto: eradicate CC_HAS_ASM_GOTO

2022-08-21T17:06:28+00:00

GCC has supported asm goto since 4.5, and Clang has since version 9.0.0.
The minimum supported versions of these tools for the build according to
Documentation/process/changes.rst are 5.1 and 11.0.0 respectively.

Remove the feature detection script, Kconfig option, and clean up some
fallback code that is no longer supported.

The removed script was also testing for a GCC specific bug that was
fixed in the 4.7 release.

Also remove workarounds for bpftrace using clang older than 9.0.0, since
other BPF backend fixes are required at this point.

Link: https://lore.kernel.org/lkml/CAK7LNATSr=BXKfkdW8f-H5VT_w=xBpT2ZQcZ7rm6JfkdE+QnmA@mail.gmail.com/
Link: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48637
Acked-by: Borislav Petkov 
Suggested-by: Masahiro Yamada 
Suggested-by: Alexei Starovoitov 
Signed-off-by: Nick Desaulniers 
Reviewed-by: Ingo Molnar 
Reviewed-by: Nathan Chancellor 
Reviewed-by: Alexandre Belloni 
Signed-off-by: Linus Torvalds

docs: kbuild: fix typo

2022-07-27T12:18:00+00:00

on -> one.

Signed-off-by: Baruch Siach 
Signed-off-by: Masahiro Yamada

Documentation/llvm: Update Supported Arch table

2022-06-19T23:21:29+00:00

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arch table in our docs that he refers to is outdated.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 
Reviewed-by: Nathan Chancellor 
Signed-off-by: Masahiro Yamada

Merge tag 'kbuild-v5.19' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild

2022-05-26T19:09:50+00:00

Pull Kbuild updates from Masahiro Yamada:

 - Add HOSTPKG_CONFIG env variable to allow users to override pkg-config

 - Support W=e as a shorthand for KCFLAGS=-Werror

 - Fix CONFIG_IKHEADERS build to support toybox cpio

 - Add scripts/dummy-tools/pahole to ease distro packagers' life

 - Suppress false-positive warnings from checksyscalls.sh for W=2 build

 - Factor out the common code of arch/*/boot/install.sh into
   scripts/install.sh

 - Support 'kernel-install' tool in scripts/prune-kernel

 - Refactor module-versioning to link the symbol versions at the final
   link of vmlinux and modules

 - Remove CONFIG_MODULE_REL_CRCS because module-versioning now works in
   an arch-agnostic way

 - Refactor modpost, Makefiles

* tag 'kbuild-v5.19' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (56 commits)
  genksyms: adjust the output format to modpost
  kbuild: stop merging *.symversions
  kbuild: link symbol CRCs at final link, removing CONFIG_MODULE_REL_CRCS
  modpost: extract symbol versions from *.cmd files
  modpost: add sym_find_with_module() helper
  modpost: change the license of EXPORT_SYMBOL to bool type
  modpost: remove left-over cross_compile declaration
  kbuild: record symbol versions in *.cmd files
  kbuild: generate a list of objects in vmlinux
  modpost: move *.mod.c generation to write_mod_c_files()
  modpost: merge add_{intree_flag,retpoline,staging_flag} to add_header
  scripts/prune-kernel: Use kernel-install if available
  kbuild: factor out the common installation code into scripts/install.sh
  modpost: split new_symbol() to symbol allocation and hash table addition
  modpost: make sym_add_exported() always allocate a new symbol
  modpost: make multiple export error
  modpost: dump Module.symvers in the same order of modules.order
  modpost: traverse the namespace_list in order
  modpost: use doubly linked list for dump_lists
  modpost: traverse unresolved symbols in order
  ...

randstruct: Move seed generation into scripts/basic/

2022-05-08T08:33:07+00:00

To enable Clang randstruct support, move the structure layout
randomization seed generation out of scripts/gcc-plugins/ into
scripts/basic/ so it happens early enough that it can be used by either
compiler implementation. The gcc-plugin still builds its own header file,
but now does so from the common "randstruct.seed" file.

Cc: linux-hardening@vger.kernel.org
Signed-off-by: Kees Cook 
Link: https://lore.kernel.org/r/20220503205503.3054173-6-keescook@chromium.org

randstruct: Reorganize Kconfigs and attribute macros

2022-05-08T08:33:06+00:00

In preparation for Clang supporting randstruct, reorganize the Kconfigs,
move the attribute macros, and generalize the feature to be named
CONFIG_RANDSTRUCT for on/off, CONFIG_RANDSTRUCT_FULL for the full
randomization mode, and CONFIG_RANDSTRUCT_PERFORMANCE for the cache-line
sized mode.

Cc: linux-hardening@vger.kernel.org
Signed-off-by: Kees Cook 
Link: https://lore.kernel.org/r/20220503205503.3054173-4-keescook@chromium.org

docs: kbuild: add references on Kconfig semantics

2022-04-06T10:27:41+00:00

Add references to 1) a research paper which provides a definition of
Kconfig semantics, 2) the kismet tool, which checks for unmet direct
dependency bugs in Kconfig specifications.

Signed-off-by: Paul Gazzillo 
Signed-off-by: Necip Fazil Yildiran 
Signed-off-by: Masahiro Yamada

kbuild: Make $(LLVM) more flexible

2022-03-31T03:03:46+00:00

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 
Suggested-by: Peter Zijlstra 
Signed-off-by: Nathan Chancellor 
Reviewed-by: Kees Cook 
Reviewed-by: Nick Desaulniers 
Signed-off-by: Masahiro Yamada

kbuild: Add environment variables for userprogs flags

2022-02-14T01:37:32+00:00

Allow additional arguments be passed to userprogs compilation.
Reproducible clang builds need to provide a sysroot and gcc path to
ensure the same toolchain is used across hosts. KCFLAGS is not currently
used for any user programs compilation, so add new USERCFLAGS and
USERLDFLAGS which serves similar purpose as HOSTCFLAGS/HOSTLDFLAGS.

Clang might detect GCC installation on hosts which have it installed
to a default location in /. With addition of these environment
variables, you can specify flags such as:

$ make USERCFLAGS=--sysroot=/path/to/sysroot

This can also be used to specify different sysroots such as musl or
bionic which may be installed on the host in paths that the compiler
may not search by default.

Signed-off-by: Elliot Berman 
Reviewed-by: Nick Desaulniers 
Reviewed-by: Fangrui Song 
Signed-off-by: Masahiro Yamada

doc: kbuild: fix default in `imply` table

2022-01-08T09:28:21+00:00

`BAZ` takes `FOO`'s value as default (as far as `BAR` allows it).

Signed-off-by: Miguel Ojeda 
Signed-off-by: Masahiro Yamada