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[Bug libc/18396] New: timezone internal code for time_t_max and time_t_min is UB
- From: "nszabolcs at gmail dot com" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Mon, 11 May 2015 17:05:32 +0000
- Subject: [Bug libc/18396] New: timezone internal code for time_t_max and time_t_min is UB
- Auto-submitted: auto-generated
https://sourceware.org/bugzilla/show_bug.cgi?id=18396
Bug ID: 18396
Summary: timezone internal code for time_t_max and time_t_min
is UB
Product: glibc
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: libc
Assignee: unassigned at sourceware dot org
Reporter: nszabolcs at gmail dot com
CC: drepper.fsp at gmail dot com
Target Milestone: ---
recent gcc change exposed an invalid -1 << n in timezone/private.h
if time_t is signed:
/* The minimum and maximum finite time values. */
static time_t const time_t_min =
(TYPE_SIGNED(time_t)
? (time_t) -1 << (CHAR_BIT * sizeof (time_t) - 1)
: 0);
static time_t const time_t_max =
(TYPE_SIGNED(time_t)
? - (~ 0 < 0) - ((time_t) -1 << (CHAR_BIT * sizeof (time_t) - 1))
: -1);
the gcc warning may get silenced as it caused other problems:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66066
but the UB should be fixed.
There is no simple solution: the above code seems to want to support
non-two's-complement signed int representations too.
I think a solution based on (uintmax_t)-1 >> n can work for time_t_max
with reasonable assumptions, otherwise arch specific soulution can be used.
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