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do_tzset() did't always reset the DST transition rules r0 and r1. That
means the rules from older TZ settings could leak into newer ones.
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this further reduces the number of source files which need to include
libc.h and thereby be potentially exposed to libc global state and
internals.
this will also facilitate further improvements like adding an inline
fast-path, if we want to do so later.
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commits leading up to this one have moved the vast majority of
libc-internal interface declarations to appropriate internal headers,
allowing them to be type-checked and setting the stage to limit their
visibility. the ones that have not yet been moved are mostly
namespace-protected aliases for standard/public interfaces, which
exist to facilitate implementing plain C functions in terms of POSIX
functionality, or C or POSIX functionality in terms of extensions that
are not standardized. some don't quite fit this description, but are
"internally public" interfacs between subsystems of libc.
rather than create a number of newly-named headers to declare these
functions, and having to add explicit include directives for them to
every source file where they're needed, I have introduced a method of
wrapping the corresponding public headers.
parallel to the public headers in $(srcdir)/include, we now have
wrappers in $(srcdir)/src/include that come earlier in the include
path order. they include the public header they're wrapping, then add
declarations for namespace-protected versions of the same interfaces
and any "internally public" interfaces for the subsystem they
correspond to.
along these lines, the wrapper for features.h is now responsible for
the definition of the hidden, weak, and weak_alias macros. this means
source files will no longer need to include any special headers to
access these features.
over time, it is my expectation that the scope of what is "internally
public" will expand, reducing the number of source files which need to
include *_impl.h and related headers down to those which are actually
implementing the corresponding subsystems, not just using them.
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This manifests itself in mktime if tm_isdst = 1 and the current TZ= is
a POSIX timezone specification. mktime would see that tm_isdst was set
to 0 by __secs_to_zone, and subtract 'oppoff' (dst_off) - gmtoff from
the resultant time. This meant that mktime returned a time that was
exactly double the GMT offset of the desired timezone when tm_isdst
was = 1.
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In all cases this is just a change from two volatile int to one.
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notes by maintainer:
both C and POSIX use the term UTC to specify related functionality,
despite POSIX defining it as something more like UT1 or historical
(pre-UTC) GMT without leap seconds. neither specifies the associated
string for %Z. old choice of "GMT" violated principle of least
surprise for users and some applications/tests. use "UTC" instead.
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the time of day at which daylight time switches over is specified in
local time in the dst state prior to the transition. the code for
handling this wrongly assumed it needed to switch whether dst or
standard offset is applied to the transition time when the dst end
date is before the dst start date (souther hemisphere summer), but in
fact the end transition time should always be adjusted for dst, and
the start transition time should always be adjusted for standard time.
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Fix parsing of the < > quoted time zone names. Compare the correct
character instead of repeatedly comparing the first character.
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tm_gmtoff is a nonstandard field, but on historical systems which have
this field, it stores the offset of the local time zone from GMT or
UTC. this is the opposite of the POSIX extern long timezone object and
the offsets used in POSIX-form TZ strings, which represent the offset
from local time to UTC. previously we were storing these negated
offsets in tm_gmtoff too.
programs which only used this field indirectly via strftime were not
affected since strftime performed the negation for presentation.
however, some programs and libraries accesse tm_gmtoff directly and
were obtaining negated time zone offsets.
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this improves compatibility with the behavior of other systems and
with some applications which set an empty TZ var to disable use of
local time by mktime, etc.
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the memory model we use internally for atomics permits plain loads of
values which may be subject to concurrent modification without
requiring that a special load function be used. since a compiler is
free to make transformations that alter the number of loads or the way
in which loads are performed, the compiler is theoretically free to
break this usage. the most obvious concern is with atomic cas
constructs: something of the form tmp=*p;a_cas(p,tmp,f(tmp)); could be
transformed to a_cas(p,*p,f(*p)); where the latter is intended to show
multiple loads of *p whose resulting values might fail to be equal;
this would break the atomicity of the whole operation. but even more
fundamental breakage is possible.
with the changes being made now, objects that may be modified by
atomics are modeled as volatile, and the atomic operations performed
on them by other threads are modeled as asynchronous stores by
hardware which happens to be acting on the request of another thread.
such modeling of course does not itself address memory synchronization
between cores/cpus, but that aspect was already handled. this all
seems less than ideal, but it's the best we can do without mandating a
C11 compiler and using the C11 model for atomics.
in the case of pthread_once_t, the ABI type of the underlying object
is not volatile-qualified. so we are assuming that accessing the
object through a volatile-qualified lvalue via casts yields volatile
access semantics. the language of the C standard is somewhat unclear
on this matter, but this is an assumption the linux kernel also makes,
and seems to be the correct interpretation of the standard.
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previously, the hours were considered as a signed quantity while
minutes and seconds were always treated as positive offsets. however,
semantically the '-' sign should negate the whole hh:mm:ss offset.
this bug only affected timezones east of GMT with non-whole-hours
offsets, such as those used in India and Nepal.
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the way this is implemented, it also allows explicit setting of
TZ=/etc/localtime even for suid programs. this is not a problem
because /etc/localtime is a trusted path, much like the trusted
zoneinfo search path.
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previously, setting TZ to the pathname of a file which was not a valid
zoneinfo file would usually cause programs using local time zone based
operations to crash. the new code checks the file size and magic at
the beginning of the file, which seems sufficient to prevent
accidental misconfiguration from causing crashes. attempting to make
fully-robust validation would be futile unless we wanted to drop use
of mmap (shared zoneinfo) and instead read it into a local buffer,
since such validation would be subject to race conditions with
modification of the file.
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since the form TZ=name is reserved for POSIX-form time zone strings,
TZ=:name needs to be used when the zoneinfo filename is in the
top-level zoneinfo directory and therefore does not contain a slash.
previously the leading colon was merely dropped, making it impossible
to access such zones without a full absolute pathname.
changes based on patch by Timo Teräs.
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the rest of the code is not prepared to handle an empty TZ string, so
falling back to __gmt ("GMT"), just as if TZ had been blank or unset,
is the preferable action.
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try+l points to \0, so only one iteration was ever tried.
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we need to skip to the second TZif header, which starts at
skip+44, and then skip another header (20 bytes) plus the following
6 32bit values.
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if sizeof(time_t) == 8, this code path was missing the correct
offset into the zoneinfo file, using the header magic to do
offset calculations.
the 6 32bit fields to be read start at offset 20.
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in this case, the first standard-time and first daylight-time rules
should be taken as the "default" ones to expose.
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if a zoneinfo file is not (or is no longer) in use, don't check the
abbrevs pointers, which may be invalid.
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this may need further revision in the future, since POSIX is rather
unclear on the requirements, and is designed around the assumption of
POSIX TZ specifiers which are not sufficiently powerful to represent
real-world timezones (this is why zoneinfo support was added).
the basic issue is that strftime gets the string and numeric offset
for the timezone from the extra fields in struct tm, which are
initialized when calling localtime/gmtime/etc. however, a conforming
application might have created its own struct tm without initializing
these fields, in which case using __tm_zone (a pointer) could crash.
other zoneinfo-based implementations simply check for a null pointer,
but otherwise can still crash of the field contains junk.
simply ignoring __tm_zone and using tzname[] would "work" but would
give incorrect results in time zones with more complex rules. I feel
like this would lower the quality of implementation.
instead, simply validate __tm_zone: unless it points to one of the
zone name strings managed by the timezone system, assume it's invalid.
this commit also fixes several other minor bugs with formatting:
tm_isdst being negative is required to suppress printing of the zone
formats, and %z was using the wrong format specifiers since the type
of val was changed, resulting in bogus output.
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the empty TZ string was matching equal to the initial value of the
cached TZ name, thus causing do_tzset never to run and never to
initialize the time zone data.
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this commit has two major user-visible parts: zoneinfo-format time
zones are now supported, and overflow handling is intended to be
complete in the sense that all functions return a correct result if
and only if the result fits in the destination type, and otherwise
return an error. also, some noticable bugs in the way DST detection
and normalization worked have been fixed, and performance may be
better than before, but it has not been tested.
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