Formerly the init functions were called in the opposite of the
order in which libraries were loaded, and libraries were loaded
according to a breadth-first traversal of the dependency graph.
That ordering came from SVR4.0, and it was easy to implement but
not always sensible.
Now we do a depth-first walk over the dependency graph and call
the init functions in an order such that each shared object's needed
objects are initialized before the shared object itself. At the
same time we build a list of finalization (fini) functions in the
opposite order, to guarantee correct C++ destructor ordering whenever
possible. (It may not be possible if dlopen and dlclose are used
in strange ways, but we come as close as one can come.)
The need for this renovation has become apparent as more programs
have started using multithreading. The multithreaded C library
libc_r requires initialization, whereas the standard libc does not.
Since virtually every other object depends on the C library, it is
important that it get initialized first.
lock against themselves, causing infinite spinning. Brian Feldman
found this problem when testing with Mozilla and supplied the fix,
which I have revised slightly.
Here is the failure scenario. A thread calls dlopen() and acquires
the writer lock. While the thread still holds the lock, a signal
is delivered and caught. The signal handler tries to call a function
which hasn't been bound yet. It thus enters the dynamic linker
and tries to acquire the reader lock. Since the writer lock is
already held, it will spin forever in the signal handler. The
thread holding the lock won't be able to progress and release the
lock.
The solution is to block almost all signals while holding the
exclusive lock.
A similar problem could conceivably occur in the opposite order.
Namely, a thread is holding the reader lock and then a signal
handler calls dlopen() or dlclose() and spins waiting for the writer
lock. We deal with this administratively by proclaiming that signal
handlers aren't allowed to call dlopen() or dlclose(). Actually
we don't have to proclaim a thing, since signal handlers aren't
allowed to call any system functions except those which are explicitly
permitted.
Submitted by: Brian Fundakowski Feldman <green>
and for all (I hope). Packages such as wine, JDK, and linuxthreads
should no longer have any problems with re-entering the dynamic
linker.
This commit replaces the locking used in the dynamic linker with a
new spinlock-based reader/writer lock implementation. Brian
Fundakowski Feldman <green> argued for this from the very beginning,
but it took me a long time to come around to his point of view.
Spinlocks are the only kinds of locks that work with all thread
packages. But on uniprocessor systems they can be inefficient,
because while a contender for the lock is spinning the holder of the
lock cannot make any progress toward releasing it. To alleviate
this disadvantage I have borrowed a trick from Sleepycat's Berkeley
DB implementation. When spinning for a lock, the requester does a
nanosleep() call for 1 usec. each time around the loop. This will
generally yield the CPU to other threads, allowing the lock holder
to finish its business and release the lock. I chose 1 usec. as the
minimum sleep which would with reasonable certainty not be rounded
down to 0.
The formerly machine-independent file "lockdflt.c" has been moved
into the architecture-specific subdirectories by repository copy.
It now contains the machine-dependent spinlocking code. For the
spinlocks I used the very nifty "simple, non-scalable reader-preference
lock" which I found at
<http://www.cs.rochester.edu/u/scott/synchronization/pseudocode/rw.html>
on all CPUs except the 80386 (the specific CPU model, not the
architecture). The 80386 CPU doesn't support the necessary "cmpxchg"
instruction, so on that CPU a simple exclusive test-and-set lock
is used instead. 80386 CPUs are detected at initialization time by
trying to execute "cmpxchg" and catching the resulting SIGILL
signal.
To reduce contention for the locks, I have revamped a couple of
key data structures, permitting all common operations to be done
under non-exclusive (reader) locking. The only operations that
require exclusive locking now are the rare intrusive operations
such as dlopen() and dlclose().
The dllockinit() interface is now deprecated. It still exists,
but only as a do-nothing stub. I plan to remove it as soon as is
reasonably possible. (From the very beginning it was clearly
labeled as experimental and subject to change.) As far as I know,
only the linuxthreads port uses dllockinit(). This interface turned
out to have several problems. As one example, when the dynamic
linker called a client-supplied locking function, that function
sometimes needed lazy binding, causing re-entry into the dynamic
linker and a big looping mess. And in any case, it turned out to be
too burdensome to require threads packages to register themselves
with the dynamic linker.
"ld-elf.so.1.old". The dynamic linker is a critical component of
the system, and it is difficult to recover if it is damaged and
there isn't a working backup available. For instance, parts of
the toolchain such as the assembler are dynamically linked, making
it impossible to build a new dynamic linker if the installed one
doesn't work.
DWARF2 exception tables emitted by the compiler for C++ sources.
These tables are tightly packed, and they contain some relocated
addresses which are not well-aligned.
really used in bsd.man.mk).
Don't uselessly set MANSRC ("." is in the path by default, and there are
no ordering problems).
Fixed some other style bugs.
interface, and statically link them to the programs using them.
These functions, upon reflection and discussion, are too generically
named for a library interface with such specific functionality.
Also the api that they use, whilst ok for private use, isn't good
enough for a libc function.
Additionally there were complications with the build/install-world
process. It depends heavily upon xinstall, which got broken by
the change in api, and caused bootstrap problems and general mayhem.
There is work in progress to address future problems that may be
caused by changes in install-chain tools, and better names for
{g|s}etflags can be derived when some future program requires them.
For now the code has been left in src/lib/libc/gen (it started off
in src/bin/ls).
It's important to provide library functions for manipulating file
flag strings if we ever want this interface to be adopted outside
of the source tree, but now isn't necessarily the right moment
with 4.0-release just around the corner.
Approved: jkh
When hostname is not set, ftpd core dumps, because there is no
NULL check for freeing name resolving information for its own
hostname.
So the check is added.
Approved by: jkh
Some of rcmd related function is need to be updated to
support IPv6. Some of them are already updated as standard
document. But there is also several de-facto functions and
they are not listed in standard documents.
They are,
iruserok() (used by rlogind, rshd)
ruserok() (used by kerberos, etc)
KAME package updated those functions in original way.
iruserok_af()
ruserok_af()
But recently there was discussion on IETF IPng mailing
list about how to sync those API, and it is decided,
-Those function is not standard and not documented.
-But let BSDs sync their API as de-facto.
And after some discussion, it is announced that
-add update to iruserok() as iruserok_sa()
-no ruserok() API change(it is only updated internaly)
So I sync those API before 4.0 is released.
The changes are,
-prototype changes
-ruserok() internal update (use iruserok_sa() inside)
-removal of ruserok_af()
-change iruserok_af() as static functioin, and also prefix the name with __.
-add iruserok_sa() (Just call __iruserok_af() inside)
-adding flag AI_ALL to getipnodebyaddr() called from __icheckhost().
This is necessary to support IPv4 communication via AF_INET6 socket
could be correctly authenticated via iruserok_sa()
-irusreok_af() call is replaced to iruserok_sa() call
in rlogind, and rshd.
Approved by: jkh
figure out which shared object(s) contain the the locking methods
and fully bind those objects as if they had been loaded with
LD_BIND_NOW=1. The goal is to keep the locking methods from
requiring any lazy binding. Otherwise infinite recursion occurs
in _rtld_bind.
This fixes the infinite recursion problem in the linuxthreads port.
just a few of them. This looks like it solves the recent
ld-elf.so.1: assert failed: /usr/src/libexec/rtld-elf/lockdflt.c:55
failures seen by some applications such as JDK.
init and fini functions. Now the code is very careful to hold no
locks when calling these functions. Thus the dynamic linker cannot
be re-entered with a lock already held.
Remove the tolerance for recursive locking that I added in revision
1.2 of dllockinit.c. Recursive locking shouldn't happen any more.
Mozilla and JDK users: I'd appreciate confirmation that things still
work right (or at least the same) with these changes.
. add Xrs to hosts.equiv(5), auth.conf(5), services(5) to some pages
. sort Xrs in SEE ALSO sections
Patches based on PR: docs/15680
Submitted by: Christian Weisgerber <naddy@mips.rhein-neckar.de>
locking functions. If an application loads a shared object with
dlopen() and the shared object has an init function which requires
lazy binding, then _rtld_bind is called when the thread is already
inside the dynamic linker. This leads to a recursive acquisition
of the lock, which I was not expecting -- hence the assert failure.
This work-around makes the default locking functions handle recursive
locking. It is NOT the correct fix -- that should be implemented
at the generic locking level rather than in the default locking
functions. I will implement the correct fix in a future commit.
Since the dllockinit() interface will likely need to change, warn
about that in both the man page and the header file.
functions to be used by the dynamic linker. This can be called by
threads packages at start-up time. I will add the call to libc_r
soon.
Also add a default locking method that is used up until dllockinit()
is called. The default method works by blocking SIGVTALRM, SIGPROF,
and SIGALRM in critical sections. It is based on the observation
that most user-space threads packages implement thread preemption
with one of these signals (usually SIGVTALRM).
The dynamic linker has never been reentrant, but it became less
reentrant in revision 1.34 of "src/libexec/rtld-elf/rtld.c".
Starting with that revision, multiple threads each doing lazy
binding could interfere with each other. The usual symptom was
that a symbol was falsely reported as undefined at start-up time.
It was rare but not unseen. This commit fixes it.
happened as it was working around problems elsewhere (ie: binutils/ld
not doing the right thing according to the ELF design). libcrypt has
been adjusted to not need the runtime -lmd. It's still not quite right
(ld is supposed to work damnit) but at least it doesn't impact all the
users of libcrypt in Marcel's cross-build model.
assumption that only getty processes can be managed. Describe the
SysV-like ability to keep arbitrary long-running processes alive
using a non-device first field in /etc/ttys.
PR: 12767
Submitted by: Peter Jeremy <peter.jeremy@alcatel.com.au>
bptypes.h originally defined int32 to be of type long. This obviously
doesn't work on the Alpha. By defining int32 (and u_int32) in terms of
int32_t (and u_int32_t) it now is what it says it should be.
Two occurrences of 'unsigned int32' have been changed to 'u_int32' for
consistency.
Submitted by: Wilko Bulte <wilko@yedi.iaf.nl>
libjava peeks into the dynamic linker's private Obj_Entry structures.
My recent changes introduced some new members near the front of
the structures, causing libjava to get the wrong fields. This commit
moves the new members toward the end of the structure so that the
layout of the portion that is relevant to JDK remains the same as
before.
I will work with the JDK porting team to see if we can come up with
a less fragile way for them to do what they need to do. I understand
the current approach was necessary in order to work around some
limitations of the dynamic linker. Maybe it's not necessary any
more.
PT_INTERP program header entry, to ensure that gdb always finds
the right dynamic linker.
Use obj->relocbase to simplify a few calculations where appropriate.
loaded separately by dlopen that have global symbols with identical
names. Viewing each dlopened object as a DAG which is linked by its
DT_NEEDED entries in the dynamic table, the search order is as
follows:
* If the referencing object was linked with -Bsymbolic, search it
internally.
* Search all dlopened DAGs containing the referencing object.
* Search all objects loaded at program start up.
* Search all objects which were dlopened() using the RTLD_GLOBAL
flag (which is now supported too).
The search terminates as soon as a strong definition is found.
Lacking that, the first weak definition is used.
These rules match those of Solaris, as best I could determine them
from its vague manual pages and the results of experiments I performed.
PR: misc/12438
violations in certain obscure cases involving failed dlopens. Many
thanks to Archie Cobbs for providing me with a good test case.
Eliminate a block that existed only to localize a declaration.
the dynamic linker didn't clean up properly. A subsequent dlopen()
of the same object would appear to succeed.
Another excellent fix from Max Khon.
PR: bin/12471
Submitted by: Max Khon <fjoe@iclub.nsu.ru>
discovered by Hidetoshi Shimokawa. Large programs need multiple
GOTs. The lazy binding stub in the PLT can be reached from any of
these GOTs, but the dynamic linker only has enough information to
fix up the first GOT entry. Thus calls through the other GOTs went
through the time-consuming lazy binding process on every call.
This fix rewrites the PLT entries themselves to bypass the lazy
binding.
Tested by Hidetoshi Shimokawa and Steve Price.
Reviewed by: Doug Rabson <dfr@freebsd.org>
o main returns int not void
o use return 0 at end of main when needed
o use braces to avoid potentially ambiguous else
o don't default to type int (and also remove a useless register
modifier).
Reviewed by: obrien and chuckr
function. It was an ill-considered feature. It didn't solve the
problem I wanted it to solve. And it added Yet Another Version
Number that would have to be maintained at every release point.
I'm nuking it now before anybody grows too fond of it.
_init() functions, initialize the global variables "__progname" and
"environ". This makes it possible for the _init() functions to call
things like getenv() and err().
the Makefile, and move it down into the architecture-specific
subdirectories.
Eliminate an asm() statement for the i386.
Make the dynamic linker work if it is built as an executable instead
of as a shared library. See i386/Makefile.inc to find out how to
do it. Note, this change is not enabled and it might never be
enabled. But it might be useful in the future. Building the
dynamic linker as an executable should make it start up faster,
because it won't have any relocations. But in practice I suspect
the difference is negligible.
MAXHOSTNAMELEN and call trimdomain() before implementing
the -u option.
This allows local hosts of a lan with a long domain name to
appear properly in utmp by base host name (w/o domain) rather
than by IP number.
friends are terminated and allow for a maximum
host name length of MAXHOSTNAMELEN - 1.
Put parenthesis around sizeof args.
Make some variables static.
Fix telnetd -u (broken by my last commit)
Prompted by: bde
lookup on the incoming IP, do a forward lookup on
the result and make sure that the IP is in the
resulting list. If it's not, put the IP number
in utmp/wtmp instead of the rogue name.
Stolen from: rlogind
Suggested by: sef
avoid crashing inside rtld (since it's easy) since everything else handles
it. Of course, if the target program checks argv[], it'll fall over.
Reviewed by: jdp
damn useful thing for using with serial consoles in clusters etc or secure
console locations. Using a custom gettytab entry for console with
an entry like 'al=root' means that there is *always* a root login ready on
the console. This should replace hacks like those which go with conserver
etc. (This is a loaded gun, watch out for those feet!)
Submitted by: "Andrew J. Korty" <ajk@purdue.edu>
There's not much point in having uucpd behave differently than
login(1) for this, and now uucpd is compatible to the default chat
script of Taylor UUCP which sends a single \r at first.
While i was at it, added a few strategic ``errno = 0;''s, so at least
an `Undefined error 0' will be returned for things like a closed
connection while reading the login ID or password, as opposed to an
even more bogus thing like `No such file or directory'.
on rshd and rlogind. However, note that:
1: rshd used to drop a connection with -a if the hostname != ip address.
This is unneeded, because iruserok() does it's own checking.
It was also wrong if .rhosts had an explicit IP address in it,
connections would be dropped from that host solely because the DNS was
mismatched even though it was explicitly intended to work by IP address.
2: rlogind and rshd check the hostname mappings by default now because that
is what goes into the utmp/wtmp and logs. If the hostname != ip address,
then it uses the IP address for logging/utmp/wtmp purposes. There isn't
much point logging ficticious hostnames.
3: rshd -a is now accepted (but ignored) for compatability. If you really
want to make life miserable for people with bad reverse DNS, use tcpd in
paranoid mode (which is questionable anyway, given DNS ttl tweaking).
Removed getuid() root check so ntalkd can be run from a tty sandbox.
It isn't suid root anyway, who knows why the getuid() check was even
in there in the first place!
rtld would accept the first shared library it found with the right
major version number, even if the minor version number was too low.
If a different version of the shared library with an adequate minor
version number appeared later in the search path, it would not be
found.
Now the rtld searches all locations first looking for a library
with a minor version that is high enough. Only if such a library
is not found will it fall back to accepting a minor version number
that is too low. As before, a warning comes out in that case.
This solves some problems encountered when building an older world
on a -current system.
References from GDB to "printf" and various other functions would
find the versions in the dynamic linker itself, rather than the
versions in the program's libc. This fix moves the GDB link map
entry for the dynamic linker to the end of the search list, where
its symbols will be found only if they are not found anywhere else.
It was suggested by Doug Rabson, though I implemented it a little
differently.
I personally would prefer to leave the dynamic linker's entry out
of the GDB search list altogether. But Doug argues that it is
handy there for such things as setting breakpoints on dlopen().
So it stays for now, at least.
Note, if we ever integrate the dynamic linker with libc (which has
several important benefits to recommend it), this whole problem
goes away.
