[PATCH v3 1/5] y2038: Introduce __ASSUME_TIME64_SYSCALLS define

[Lukasz Majewski <lukma at denx dot de>]

This define indicates if the Linux kernel (5.1+) provides 64 bit versions
of time related syscalls (e.g. clock_settime64).

Those syscalls are now (starting from Linux 5.1) available on actively
supported Linux architectures: arm, arm64 (compat mode), m68k, microblaze,
mips, parisc, powerpc, s390, sh, sparc, x86, xtensa.

For x32 this flag is explicitly undefined as this architecture uses time
related syscalls from x86_64 (as if it were __WORDSIZE==64 && __TIMESIZE==64).


* sysdeps/unix/sysv/linux/kernel-features.h: (__ASSUME_TIME64_SYSCALLS):
[__LINUX_KERNEL_VERSION >= 0x050100]: Define.
* sysdeps/unix/sysv/linux/x86_64/kernel-features.h (__ASSUME_TIME64_SYSCALLS):
#undef the __ASSUME_TIME64_SYSCALLS for x32 architecture

---
Changes for v3:
- Provide more detailed and verbose description
- Change name to __ASSUME_TIME64_SYSCALLS
- Undefine __ASSUME_TIME64_SYSCALLS on x32

Changes for v2:
- New patch
---
 sysdeps/unix/sysv/linux/kernel-features.h        | 38 ++++++++++++++++++++++++
 sysdeps/unix/sysv/linux/x86_64/kernel-features.h |  9 ++++++
 2 files changed, 47 insertions(+)

diff --git a/sysdeps/unix/sysv/linux/kernel-features.h b/sysdeps/unix/sysv/linux/kernel-features.h
index bc5c959f58..d2ed6f5679 100644
--- a/sysdeps/unix/sysv/linux/kernel-features.h
+++ b/sysdeps/unix/sysv/linux/kernel-features.h
@@ -143,3 +143,41 @@
    */
 
 #define __ASSUME_CLONE_DEFAULT 1
+
+#include <bits/wordsize.h>
+#if __WORDSIZE != 64
+/* Support for 64 bit version of time related Linux syscalls.
+
+   1. Architectures with __WORDSIZE==64 && __TIMESIZE==64 (e.g. x86_64,
+      aarch64) - this flag is never defined (as those already use 64 bit
+      syscalls to handle time).
+
+   2. Architectures with __WORDSIZE==32 && __TIMESIZE==32 (e.g. arm, x86)
+   2a. With Y2038 support - userspace must be compiled with
+       -D_TIME_BITS == 64 and as a result __USE_TIME_BITS64 defined
+       (time_t is an alias to time64_t in glibc's exported headers)
+
+       Those systems would use 64 bit Linux system calls to provide 64 bit
+       time support.
+
+   2b. Without Y2038 support (-D_TIME_BITS not defined or not equal to 64)
+       Such systems would use internally (in glibc) calls to 64 bit syscalls
+       with returning overflow errors after Y2038.
+
+   3. Architectures with __WORDSIZE==32 && __TIMESIZE==64
+   3a. __TIMESIZE==64 due to architecture design (for now it is only 'x32')
+       This is a special case as 'x32' architecture has 64 bit size of
+       registers but longs and pointers are 32 bit.
+       It shall use the same time related syscalls as x86_64, so the flag
+       shall be explicitly undefined.
+   3b. __TIMESIZE==64 imposed by software development (in both cases discussed
+         below the __USE_TIME_BITS64 is defined by default):
+       - For new 32 bit architectures glibc support with 64 bit time support
+         from the outset (which beforehand requires proper syscalls from
+         kernel)
+       - After the 64 bit time support conversion is finished (i.e. arm with
+         Y2038 support).  */
+# if __LINUX_KERNEL_VERSION >= 0x050100
+#  define __ASSUME_TIME64_SYSCALLS 1
+# endif
+#endif
diff --git a/sysdeps/unix/sysv/linux/x86_64/kernel-features.h b/sysdeps/unix/sysv/linux/x86_64/kernel-features.h
index 26280f57ec..e1e923f497 100644
--- a/sysdeps/unix/sysv/linux/x86_64/kernel-features.h
+++ b/sysdeps/unix/sysv/linux/x86_64/kernel-features.h
@@ -24,3 +24,12 @@
 #endif
 
 #include_next <kernel-features.h>
+
+/* For x32, which is a special case in respect to 64 bit time support,
+   the __ASSUME_TIME64_SYSCALLS define needs to be explicitly undefined.
+
+   It uses Linux time related syscalls for x86_64 (in compatibility
+   mode).  */
+#ifdef __ILP32__
+# undef __ASSUME_TIME64_SYSCALLS
+#endif
-- 
2.11.0