[PATCH, RFC] byteorder: sanity check toolchain vs kernel endianess

[Christoph Hellwig]

When removing some dead big endian checks in the RISC-V code Nick
suggested that we should have some generic sanity checks.  I don't think
we should have thos inside the RISC-V code, but maybe it might make
sense to have these in the generic byteorder headers.  Note that these
are UAPI headers and some compilers might not actually define
__BYTE_ORDER__, so we first check that it actually exists.

Suggested-by: Nick Kossifidis <mick@xxxxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 include/uapi/linux/byteorder/big_endian.h    | 4 ++++
 include/uapi/linux/byteorder/little_endian.h | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/include/uapi/linux/byteorder/big_endian.h b/include/uapi/linux/byteorder/big_endian.h
index 2199adc6a6c2..34a5864526d2 100644
--- a/include/uapi/linux/byteorder/big_endian.h
+++ b/include/uapi/linux/byteorder/big_endian.h
@@ -2,6 +2,10 @@
 #ifndef _UAPI_LINUX_BYTEORDER_BIG_ENDIAN_H
 #define _UAPI_LINUX_BYTEORDER_BIG_ENDIAN_H
 
+#if defined(__BYTE_ORDER__) && __BYTE_ORDER__ != __ORDER_BIG_ENDIAN__
+#error "Unsupported endianess, check your toolchain"
+#endif
+
 #ifndef __BIG_ENDIAN
 #define __BIG_ENDIAN 4321
 #endif
diff --git a/include/uapi/linux/byteorder/little_endian.h b/include/uapi/linux/byteorder/little_endian.h
index 601c904fd5cd..0cdf3583e19f 100644
--- a/include/uapi/linux/byteorder/little_endian.h
+++ b/include/uapi/linux/byteorder/little_endian.h
@@ -2,6 +2,10 @@
 #ifndef _UAPI_LINUX_BYTEORDER_LITTLE_ENDIAN_H
 #define _UAPI_LINUX_BYTEORDER_LITTLE_ENDIAN_H
 
+#if defined(__BYTE_ORDER__) && __BYTE_ORDER__ !=  __ORDER_LITTLE_ENDIAN__
+#error "Unsupported endianess, check your toolchain"
+#endif
+
 #ifndef __LITTLE_ENDIAN
 #define __LITTLE_ENDIAN 1234
 #endif
-- 
2.20.1