Re: utmp 64 bit time_t support

[Paul Eggert <eggert@cs.ucla.edu>]

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On 2023-08-04 00:28, Andreas Schwab wrote:
> It could just re-interpret the timestamp field as an unsigned number.

Thanks for suggesting that. Although it a hack, it's likely better than 
the hack that was already in Gnulib, so I installed the attached patch 
into Gnulib. We can use this as an idea for fixing glibc bug 30701.

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From 0a7a71a4f24b4608662b4532bd17aef758f049fd Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Sat, 5 Aug 2023 11:16:12 -0700
Subject: [PATCH] readutmp: anticipate Y2038 hack for utmp

* lib/readutmp.c (struct utmpx32): Use unsigned int for tv_sec,
not int, as that is more likely to work after 2038.
Suggested by Andreas Schwab in:
https://sourceware.org/pipermail/libc-alpha/2023-August/150661.html
---
 ChangeLog      | 6 ++++++
 lib/readutmp.c | 7 ++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index e1437b1b41..80ac7184d8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2023-08-05  Paul Eggert  <eggert@cs.ucla.edu>
 
+	readutmp: anticipate Y2038 hack for utmp
+	* lib/readutmp.c (struct utmpx32): Use unsigned int for tv_sec,
+	not int, as that is more likely to work after 2038.
+	Suggested by Andreas Schwab in:
+	https://sourceware.org/pipermail/libc-alpha/2023-August/150661.html
+
 	diffseq: simplify lint removal
 	* lib/diffseq.h (IF_LINT): Remove.
 	Instead, always ignore the diagnostic, as that’s simpler
diff --git a/lib/readutmp.c b/lib/readutmp.c
index ac1c851e97..b8eba076fa 100644
--- a/lib/readutmp.c
+++ b/lib/readutmp.c
@@ -491,7 +491,12 @@ copy_utmp_entry (STRUCT_UTMP *dst, STRUCT_UTMP *src)
     int ut_session;			/* Session ID, used for windowing.  */
     struct
     {
-      int tv_sec;			/* Seconds.  */
+      /* Seconds.  Unsigned not signed, as glibc did not exist before 1970,
+         and if the format is still in use after 2038 its timestamps
+         will surely have the sign bit on.  This hack stops working
+         at 2106-02-07 06:28:16 UTC.  */
+      unsigned int tv_sec;
+
       int tv_usec;			/* Microseconds.  */
     } ut_tv;				/* Time entry was made.  */
     int ut_addr_v6[4];			/* Internet address of remote host.  */
-- 
2.39.2