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Masahiro Yamada 205b5f80c7 kconfig: introduce m32-flag and m64-flag
[ Upstream commit 8cc4fd7350 ]

When a compiler supports multiple architectures, some compiler features
can be dependent on the target architecture.

This is typical for Clang, which supports multiple LLVM backends.
Even for GCC, we need to take care of biarch compiler cases.

It is not a problem when we evaluate cc-option in Makefiles because
cc-option is tested against the flag in question + $(KBUILD_CFLAGS).

The cc-option in Kconfig, on the other hand, does not accumulate
tested flags. Due to this simplification, it could potentially test
cc-option against a different target.

At first, Kconfig always evaluated cc-option against the host
architecture.

Since commit e8de12fb7c ("kbuild: Check for unknown options with
cc-option usage in Kconfig and clang"), in case of cross-compiling
with Clang, the target triple is correctly passed to Kconfig.

The case with biarch GCC (and native build with Clang) is still not
handled properly. We need to pass some flags to specify the target
machine bit.

Due to the design, all the macros in Kconfig are expanded in the
parse stage, where we do not know the target bit size yet.

For example, arch/x86/Kconfig allows a user to toggle CONFIG_64BIT.
If a compiler flag -foo depends on the machine bit, it must be tested
twice, one with -m32 and the other with -m64.

However, -m32/-m64 are not always recognized. So, this commits adds
m64-flag and m32-flag macros. They expand to -m32, -m64, respectively
if supported. Or, they expand to an empty string if unsupported.

The typical usage is like this:

  config FOO
          bool
          default $(cc-option,$(m64-flag) -foo) if 64BIT
          default $(cc-option,$(m32-flag) -foo)

This is clumsy, but there is no elegant way to handle this in the
current static macro expansion.

There was discussion for static functions vs dynamic functions.
The consensus was to go as far as possible with the static functions.
(https://lkml.org/lkml/2018/3/2/22)

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: George Spelvin <lkml@sdf.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2020-04-08 09:08:37 +02:00
Documentation dt-bindings: net: FMan erratum A050385 2020-04-01 11:01:52 +02:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch arm64: dts: ls1046ardb: set RGMII interfaces to RGMII_ID mode 2020-04-02 15:11:03 +02:00
block block, bfq: fix overwrite of bfq_group pointer in bfq_find_set_group() 2020-03-25 08:25:49 +01:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto crypto: rename sm3-256 to sm3 in hash_algo_name 2020-02-28 17:22:26 +01:00
drivers nvme-rdma: Avoid double freeing of async event data 2020-04-08 09:08:37 +02:00
fs libfs: fix infoleak in simple_attr_read() 2020-04-01 11:02:17 +02:00
include libceph: fix alloc_msg_with_page_vector() memory leaks 2020-04-02 15:11:02 +02:00
init kbuild: remove header compile test 2020-03-05 16:43:47 +01:00
ipc Revert "ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()" 2020-02-28 17:22:20 +01:00
kernel bpf: Explicitly memset some bpf info structures declared on the stack 2020-04-02 15:11:01 +02:00
lib kbuild: move headers_check rule to usr/include/Makefile 2020-03-05 16:43:47 +01:00
mm mm: fork: fix kernel_stack memcg stats for various stack implementations 2020-04-01 11:02:03 +02:00
net libceph: fix alloc_msg_with_page_vector() memory leaks 2020-04-02 15:11:02 +02:00
samples samples/bpf: Set -fno-stack-protector when building BPF programs 2020-02-24 08:36:36 +01:00
scripts kconfig: introduce m32-flag and m64-flag 2020-04-08 09:08:37 +02:00
security efi: Only print errors about failing to get certs if EFI vars are found 2020-03-12 13:00:14 +01:00
sound ALSA: hda/realtek: Fix pop noise on ALC225 2020-03-25 08:25:59 +01:00
tools perf map: Fix off by one in strncpy() size argument 2020-04-02 15:11:02 +02:00
usr kbuild: fix 'No such file or directory' warning when cleaning 2020-03-12 13:00:09 +01:00
virt KVM: Check for a bad hva before dropping into the ghc slow path 2020-03-05 16:43:48 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap ARM: SoC fixes 2019-11-10 13:41:59 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: Update drm/i915 bug filing URL 2020-02-28 17:22:19 +01:00
Makefile Linux 5.4.30 2020-04-02 15:11:03 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.