linux-kernel - [PATCH v3] uapi: Make __{u,s}64 match {u,}int64

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Date:   Tue, 21 Jun 2022 14:03:55 +0200
From:   Cyril Hrubis <chrubis@...e.cz>
To:     linux-kernel@...r.kernel.org
Cc:     linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        libc-alpha@...rceware.org, arnd@...db.de, ltp@...ts.linux.it,
        David.Laight@...lab.com, zack@...folio.org, dhowells@...hat.com,
        Cyril Hrubis <chrubis@...e.cz>
Subject: [PATCH v3] uapi: Make __{u,s}64 match {u,}int64_t in userspace

This changes the __u64 and __s64 in userspace on 64bit platforms from
long long (unsigned) int to just long (unsigned) int in order to match
the uint64_t and int64_t size in userspace for C code.

We cannot make the change for C++ since that would be non-backwards
compatible change and may cause possible regressions and even
compilation failures, e.g. overloaded function may no longer find a
correct match.

This allows us to use the kernel structure definitions in userspace in C
code. For example we can use PRIu64 and PRId64 modifiers in printf() to
print structure membere. Morever with this there would be no need to
redefine these structures in an libc implementations as it is done now.

Consider for example the newly added statx() syscall. If we use the
header from uapi we will get warnings when attempting to print it's
members as:

	printf("%" PRIu64 "\n", stx.stx_size);

We get:

	warning: format '%lu' expects argument of type 'long unsigned int',
	         but argument 5 has type '__u64' {aka 'long long unsigned int'}

Signed-off-by: Cyril Hrubis <chrubis@...e.cz>
---
 include/uapi/asm-generic/types.h | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

v2: Make sure we do not break C++ applications
v3: Update commit message to explain C++ exclusion

diff --git a/include/uapi/asm-generic/types.h b/include/uapi/asm-generic/types.h
index dfaa50d99d8f..11e468a39d1e 100644
--- a/include/uapi/asm-generic/types.h
+++ b/include/uapi/asm-generic/types.h
@@ -1,9 +1,16 @@
 /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
 #ifndef _ASM_GENERIC_TYPES_H
 #define _ASM_GENERIC_TYPES_H
+
+#include <asm/bitsperlong.h>
+
 /*
- * int-ll64 is used everywhere now.
+ * int-ll64 is used everywhere in kernel now.
  */
-#include <asm-generic/int-ll64.h>
+#if !defined(__KERNEL__) && !defined(__cplusplus) && __BITSPERLONG == 64
+# include <asm-generic/int-l64.h>
+#else
+# include <asm-generic/int-ll64.h>
+#endif

 #endif /* _ASM_GENERIC_TYPES_H */
-- 
2.35.1