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From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Masahiro Yamada <masahiroy@kernel.org>,
	George Spelvin <lkml@sdf.org>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Sasha Levin <sashal@kernel.org>,
	linux-kbuild@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: [PATCH AUTOSEL 5.5 06/28] kconfig: introduce m32-flag and m64-flag
Date: Thu, 26 Mar 2020 19:23:35 -0400
Message-ID: <20200326232357.7516-6-sashal@kernel.org> (raw)
In-Reply-To: <20200326232357.7516-1-sashal@kernel.org>

From: Masahiro Yamada <masahiroy@kernel.org>

[ Upstream commit 8cc4fd73501d9f1370c3eebb70cfe8cc9e24062b ]

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 e8de12fb7cde ("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>
---
 scripts/Kconfig.include | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include
index bfb44b265a948..77a69ba9cd198 100644
--- a/scripts/Kconfig.include
+++ b/scripts/Kconfig.include
@@ -40,3 +40,10 @@ $(error-if,$(success, $(LD) -v | grep -q gold), gold linker '$(LD)' not supporte
 
 # gcc version including patch level
 gcc-version := $(shell,$(srctree)/scripts/gcc-version.sh $(CC))
+
+# machine bit flags
+#  $(m32-flag): -m32 if the compiler supports it, or an empty string otherwise.
+#  $(m64-flag): -m64 if the compiler supports it, or an empty string otherwise.
+cc-option-bit = $(if-success,$(CC) -Werror $(1) -E -x c /dev/null -o /dev/null,$(1))
+m32-flag := $(cc-option-bit,-m32)
+m64-flag := $(cc-option-bit,-m64)
-- 
2.20.1


  parent reply index

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-26 23:23 [PATCH AUTOSEL 5.5 01/28] thunderbolt: Fix error code in tb_port_is_width_supported() Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 02/28] drm/bridge: dw-hdmi: fix AVI frame colorimetry Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 03/28] nvme-rdma: Avoid double freeing of async event data Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 04/28] ALSA: hda/realtek: Fix pop noise on ALC225 Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 05/28] staging: wfx: fix warning about freeing in-use mutex during device unregister Sasha Levin
2020-03-26 23:23 ` Sasha Levin [this message]
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 07/28] int128: fix __uint128_t compiler test in Kconfig Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 08/28] drm/amdgpu: add fbdev suspend/resume on gpu reset Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 09/28] drm/amd/display: Add link_rate quirk for Apple 15" MBP 2017 Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 10/28] drm/bochs: downgrade pci_request_region failure from error to warning Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 11/28] initramfs: restore default compression behavior Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 12/28] staging: greybus: loopback_test: fix potential path truncation Sasha Levin
2020-03-27  6:28   ` Greg KH
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 13/28] staging: greybus: loopback_test: fix potential path truncations Sasha Levin
2020-03-27  6:28   ` Greg Kroah-Hartman
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 14/28] arm64: smp: fix smp_send_stop() behaviour Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 15/28] arm64: smp: fix crash_smp_send_stop() behaviour Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 16/28] modpost: Get proper section index by get_secindex() instead of st_shndx Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 17/28] drm/amdgpu: fix typo for vcn1 idle check Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 18/28] tools/power turbostat: Fix gcc build warnings Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 19/28] tools/power turbostat: Fix missing SYS_LPI counter on some Chromebooks Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 20/28] tools/power turbostat: Fix 32-bit capabilities warning Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 21/28] nvmet-tcp: set MSG_MORE only if we actually have more to send Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 22/28] btrfs: fix removal of raid[56|1c34} incompat flags after removing block group Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 23/28] kconfig: Add yes2modconfig and mod2yesconfig targets Sasha Levin
2020-03-26 23:41   ` Tetsuo Handa
2020-03-27  6:26   ` Greg KH
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 24/28] ALSA: pcm: oss: Avoid plugin buffer overflow Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 25/28] ALSA: line6: Fix endless MIDI read loop Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 26/28] ALSA: pcm: oss: Remove WARNING from snd_pcm_plug_alloc() checks Sasha Levin
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 27/28] tty: fix compat TIOCGSERIAL leaking uninitialized memory Sasha Levin
2020-03-27  6:27   ` Greg KH
2020-03-26 23:23 ` [PATCH AUTOSEL 5.5 28/28] drm/lease: fix WARNING in idr_destroy Sasha Levin

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