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

[Masahiro Yamada]

Hi Arnd,


2018-02-03 0:40 GMT+09:00 Arnd Bergmann <arnd@xxxxxxxx>:
> 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


Is this patch only for stable kernel,
not for the mainline?


> 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
>

If all architectures define
CONFIG_CPU_BIG_ENDIAN or CONFIG_CPU_LITTLE_ENDIAN,
is it possible to use this for endian test?

i.e.

Is it possible to replace like this?
   #ifdef __BIG_ENDIAN       ->  #ifdef CONFIG_CPU_BIG_ENDIAN

   #ifdef __LITTLE_ENDIAN     -> #ifdef CONFIG_CPU_LITTLE_ENDIAN






-- 
Best Regards
Masahiro Yamada