[PATCH 2/2] Kbuild: always define endianess in kconfig.h

[Arnd Bergmann]

Build testing with LTO found a couple of files that get compiled
differently depending on whether asm/byteorder.h gets included early
enough or not. In particular, include/asm-generic/qrwlock_types.h is
affected by this, but there are probably others as well.

The symptom is a series of LTO link time warnings, including these:

net/netlabel/netlabel_unlabeled.h:223: error: type of 'netlbl_unlhsh_add' does not match original declaration [-Werror=lto-type-mismatch]
 int netlbl_unlhsh_add(struct net *net,
net/netlabel/netlabel_unlabeled.c:377: note: 'netlbl_unlhsh_add' was previously declared here

include/net/ipv6.h:360: error: type of 'ipv6_renew_options_kern' does not match original declaration [-Werror=lto-type-mismatch]
 ipv6_renew_options_kern(struct sock *sk,
net/ipv6/exthdrs.c:1162: note: 'ipv6_renew_options_kern' was previously declared here

net/core/dev.c:761: note: 'dev_get_by_name_rcu' was previously declared here
 struct net_device *dev_get_by_name_rcu(struct net *net, const char *name)
net/core/dev.c:761: note: code may be misoptimized unless -fno-strict-aliasing is used

drivers/gpu/drm/i915/i915_drv.h:3377: error: type of 'i915_gem_object_set_to_wc_domain' does not match original declaration [-Werror=lto-type-mismatch]
 i915_gem_object_set_to_wc_domain(struct drm_i915_gem_object *obj, bool write);
drivers/gpu/drm/i915/i915_gem.c:3639: note: 'i915_gem_object_set_to_wc_domain' was previously declared here

include/linux/debugfs.h:92:9: error: type of 'debugfs_attr_read' does not match original declaration [-Werror=lto-type-mismatch]
 ssize_t debugfs_attr_read(struct file *file, char __user *buf,
fs/debugfs/file.c:318: note: 'debugfs_attr_read' was previously declared here

include/linux/rwlock_api_smp.h:30: error: type of '_raw_read_unlock' does not match original declaration [-Werror=lto-type-mismatch]
 void __lockfunc _raw_read_unlock(rwlock_t *lock) __releases(lock);
kernel/locking/spinlock.c:246:26: note: '_raw_read_unlock' was previously declared here

include/linux/fs.h:3308:5: error: type of 'simple_attr_open' does not match original declaration [-Werror=lto-type-mismatch]
 int simple_attr_open(struct inode *inode, struct file *file,
fs/libfs.c:795: note: 'simple_attr_open' was previously declared here

All of the above are caused by include/asm-generic/qrwlock_types.h failing
to include asm/byteorder.h after commit e0d02285f16e ("locking/qrwlock:
Use 'struct qrwlock' instead of 'struct __qrwlock'") in linux-4.15.

Similar bugs may or may not exist in older kernels as well, but there
is no easy way to test those with link-time optimizations, and kernels
before 4.14 are harder to fix because they don't have Babu's patch series

We had similar issues with CONFIG_ symbols in the past and ended up
always including the configuration headers though linux/kconfig.h.
This works around the issue through that same file, defining either
__BIG_ENDIAN or __LITTLE_ENDIAN depending on CONFIG_CPU_BIG_ENDIAN,
which is now always set on all architectures since commit 4c97a0c8fee3
("arch: define CPU_BIG_ENDIAN for all fixed big endian archs").

Cc: stable@xxxxxxxxxxxxxxx
Cc: Babu Moger <babu.moger@xxxxxxxxxx>
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
 include/linux/kconfig.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/kconfig.h b/include/linux/kconfig.h
index fec5076eda91..cc8fa109cfa3 100644
--- a/include/linux/kconfig.h
+++ b/include/linux/kconfig.h
@@ -4,6 +4,12 @@
 
 #include <generated/autoconf.h>
 
+#ifdef CONFIG_CPU_BIG_ENDIAN
+#define __BIG_ENDIAN 4321
+#else
+#define __LITTLE_ENDIAN 1234
+#endif
+
 #define __ARG_PLACEHOLDER_1 0,
 #define __take_second_arg(__ignored, val, ...) val
 
-- 
2.9.0