diff --git a/ChangeLog b/ChangeLog index c69f63fcfe..fcad4ff9ff 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,8 +1,14 @@ +1998-07-29 Mark Kettenis + + * sysdeps/mach/hurd/dl-sysdep.c (__lseek): New function. + (__getpid): New function. + (abort): New function. + 1998-07-29 15:07 Ulrich Drepper * sysdeps/arm/fpu/Dist: New file. Add ieee754.h. - * nis/nis_chache2_xdr.c: Removed. + * nis/nis_cache2_xdr.c: Removed. * nis/nis_cache.c: Removed. * nis/nis_cache2.h: Removed. diff --git a/linuxthreads/Banner b/linuxthreads/Banner index c1a3821f13..37c35586be 100644 --- a/linuxthreads/Banner +++ b/linuxthreads/Banner @@ -1 +1 @@ -linuxthreads-0.7 by Xavier Leroy +linuxthreads-0.8 by Xavier Leroy diff --git a/linuxthreads/ChangeLog b/linuxthreads/ChangeLog index 3027bd1655..c3f7dc3dc8 100644 --- a/linuxthreads/ChangeLog +++ b/linuxthreads/ChangeLog @@ -1,3 +1,20 @@ +1998-07-29 Xavier Leroy + + * Banner: Bump version number to 0.8 + * FAQ.html: Many updates, in particular w.r.t. debugging. + * manager.c: Support for non-default stacksize for + LinuxThreads-allocated stacks; + don't use guard pages for stacks with default size, rely on + rlimit(RLIMIT_STACK) instead (it's cheaper). + * attr.c: Likewise. + * cancel.c: Use __pthread_sig_cancel and __pthread_sig_restart + everywhere instead of PTHREAD_SIG_CANCEL and PTHREAD_SIG_RESTART. + * condvar.c: Likewise. + * internals.h: Likewise. + * restart.h: Likewise. + * signals.c: Likewise. + * pthread.c: Likewise; set rlimit(RLIMIT_STACK) as we need it. + 1998-07-23 Andreas Schwab * weaks.c: Define pthread_mutexattr_[sg]ettype instead of diff --git a/linuxthreads/FAQ.html b/linuxthreads/FAQ.html index 45d2387db2..e0de566c6a 100644 --- a/linuxthreads/FAQ.html +++ b/linuxthreads/FAQ.html @@ -5,6 +5,7 @@

LinuxThreads Frequently Asked Questions
(with answers)

+

[For LinuxThreads version 0.8]

@@ -14,7 +15,7 @@ D. Problems, weird behaviors, potential bugs
E. Missing functions, wrong types, etc
F. C++ issues
-G. Debugging LinuxThreads programs
+G. Debugging LinuxThreads programs
H. Compiling multithreaded code; errno madness
I. X-Windows and other libraries
J. Signals and threads
@@ -30,7 +31,7 @@ LinuxThreads is a Linux library for multi-threaded programming. It implements the Posix 1003.1c API (Application Programming Interface) for threads. It runs on any Linux system with kernel 2.0.0 -or more recent, and a suitable C library (see section B). +or more recent, and a suitable C library (see section C).

A.2: What are threads?

@@ -61,7 +62,7 @@ I/O, and graphical user interfaces.

It's an API for multi-threaded programming standardized by IEEE as part of the POSIX standards. Most Unix vendors have endorsed the POSIX 1003.1c standard. Implementations of the 1003.1c API are -already available under Sun Solaris 2.5, Digital Unix 4.0, +already available under Sun Solaris 2.5, Digital Unix 4.0, Silicon Graphics IRIX 6, and should soon be available from other vendors such as IBM and HP. More generally, the 1003.1c API is replacing relatively quickly the proprietary threads library that were @@ -176,11 +177,27 @@ including 1003.1c, with some extensions and clarifications.

C.1: Which version of the C library should I use with LinuxThreads?

-Most current Linux distributions come with libc version 5, maintained -by H.J.Lu. For LinuxThreads to work properly, you must use either -libc 5.2.18 or libc 5.4.12 or later. Avoid 5.3.12 and 5.4.7: these -have problems with the per-thread errno variable. -

+The best choice by far is glibc 2, a.k.a. libc 6. It offers very good +support for multi-threading, and LinuxThreads has been closely +integrated with glibc 2. The glibc 2 distribution contains the +sources of a specially adapted version of LinuxThreads.

+ +glibc 2 comes preinstalled as the default C library on several Linux +distributions, such as RedHat 5.0 and 5.1, and recent beta versions of +Debian. Those distributions include the version of LinuxThreads matching +glibc 2.

+ +

C.2: My system has libc 5 preinstalled, not glibc +2. Can I still use LinuxThreads?

+ +Yes, but you're likely to run into some problems, as libc 5 only +offers minimal support for threads and contains some bugs that affect +multithreaded programs.

+ +The versions of libc 5 that work best with LinuxThreads are +libc 5.2.18 on the one hand, and libc 5.4.12 or later on the other hand. +Avoid 5.3.12 and 5.4.7: these have problems with the per-thread errno +variable.

Unfortunately, many popular Linux distributions (e.g. RedHat 4.2) come with libc 5.3.12 preinstalled -- the one that does not work with @@ -190,30 +207,21 @@ of RedHat 4, there is a RPM package for libc-5.4 in the "contrib" area of RedHat FTP sites.

-

C.2: What about glibc 2, a.k.a. libc 6?

- -It's the next generation libc for Linux, developed by Ulrich -Drepper and other FSF collaborators. glibc 2 offers much better -support for threads than libc 5. Indeed, thread support was -planned from the very early stages of glibc 2, while it's a -last-minute addition to libc 5. glibc 2 actually comes with a -specially adapted version of LinuxThreads, which you can drop in the -glibc 2 sources as an add-on package. -

C.3: So, should I switch to glibc 2, or stay with a recent libc 5?

-Depends how you plan to do it. Switching an already installed +I'd recommend you switch to glibc 2. Even for single-threaded +programs, glibc 2 is more solid and more standard-conformant than libc +5. And the shortcomings of libc 5 almost preclude any serious +multi-threaded programming.

+ +Switching an already installed system from libc 5 to glibc 2 is not completely straightforward. See the Glibc2 -HOWTO for more information. -But (re-)installing a Linux distribution based on glibc 2 is easy. -One such distribution available now is RedHat 5.0. Debian and other -Linux distributors will also provide glibc 2-based distributions in the -near future. -

+HOWTO for more information. Much easier is (re-)installing a +Linux distribution based on glibc 2, such as RedHat 5.1.

-

C.4: Where can I find glibc 2 and the version of +

C.4: Where can I find glibc 2 and the version of LinuxThreads that goes with it?

On prep.ai.mit.edu and its many, many mirrors around the world. @@ -221,6 +229,14 @@ See http://www.gnu.org/order/ftp.html for a list of mirrors.

+

C.5: Where can I find libc 5 and the version of +LinuxThreads that goes with it?

+ +For libc 5, see ftp://sunsite.unc.edu/pub/Linux/devel/GCC/.

+ +For the libc 5 version of LinuxThreads, see +ftp://ftp.inria.fr/INRIA/Projects/cristal/Xavier.Leroy/linuxthreads/.

+

@@ -230,14 +246,14 @@ for a list of mirrors.

file libc_r/dirent.c You probably mean: -

 
+
         libc_r/dirent.c:94: structure has no member named `dd_lock'
 

 I haven't actually seen this problem, but several users reported it.
 My understanding is that something is wrong in the include files of
 your Linux installation (/usr/include/*). Make sure
-you're using a supported version of the C library. (See section B).

+you're using a supported version of the libc 5 library. (See question C.2).

 
 
D.2: When I compile LinuxThreads, I run into problems with
 /usr/include/sched.h: there are several occurrences of
@@ -246,7 +262,7 @@ HREF="#B">B).

 Yes, /usr/include/sched.h that comes with libc 5.3.12 is broken.
 Replace it with the sched.h file contained in the
 LinuxThreads distribution.  But really you should not be using libc
-5.3.12 with LinuxThreads! (See question C.1.)

+5.3.12 with LinuxThreads! (See question C.1.)

 
 
D.3: My program does fdopen() on a file
 descriptor opened on a pipe.  When I link it with LinuxThreads,
@@ -262,7 +278,7 @@ You wouldn't be using glibc 2.0, by any chance?  That's a known bug
 with glibc 2.0.  Please upgrade to 2.0.1 or later.

 
 
D.5: When I'm running a program that creates N
-threads, top or ps 
+threads, top or ps
 display N+2 processes that are running my program. What do all these
 processes correspond to?

 
@@ -279,39 +295,53 @@ is strong contention on a mutex: instead of giving the mutex to each
 thread in turn, it seems that it's almost always the same thread that
 gets the mutex. Isn't this completely broken behavior?

 
-What happens is the following: when a thread unlocks a mutex, all
-other threads that were waiting on the mutex are sent a signal which
-makes them runnable.  However, the kernel scheduler may or may not
-restart them immediately.  If the thread that unlocked the mutex
-tries to lock it again immediately afterwards, it is likely that it
-will succeed, because the threads haven't yet restarted.  This results
-in an apparently very unfair behavior, when the same thread repeatedly
-locks and unlocks the mutex, while other threads can't lock the mutex.

+That behavior has mostly disappeared in recent releases of
+LinuxThreads (version 0.8 and up).  It was fairly common in older
+releases, though.
 
-This is perfectly acceptable behavior with respect to the POSIX
-standard: for the default scheduling policy, POSIX makes no guarantees
-of fairness, such as "the thread waiting for the mutex for the longest
-time always acquires it first".  This allows implementations of
-mutexes to remain simple and efficient.  Properly written
-multithreaded code avoids that kind of heavy contention on mutexes,
-and does not run into fairness problems.  If you need scheduling
-guarantees, you should consider using the real-time scheduling
-policies SCHED_RR and SCHED_FIFO, which have
-precisely defined scheduling behaviors. 

+What happens in LinuxThreads 0.7 and before is the following: when a
+thread unlocks a mutex, all other threads that were waiting on the
+mutex are sent a signal which makes them runnable.  However, the
+kernel scheduler may or may not restart them immediately.  If the
+thread that unlocked the mutex tries to lock it again immediately
+afterwards, it is likely that it will succeed, because the threads
+haven't yet restarted.  This results in an apparently very unfair
+behavior, when the same thread repeatedly locks and unlocks the mutex,
+while other threads can't lock the mutex.

+
+In LinuxThreads 0.8 and up, pthread_unlock restarts only
+one waiting thread, and pre-assign the mutex to that thread.  Hence,
+if the thread that unlocked the mutex tries to lock it again
+immediately, it will block until other waiting threads have had a
+chance to lock and unlock the mutex.  This results in much fairer
+scheduling.

+
+Notice however that even the old "unfair" behavior is perfectly
+acceptable with respect to the POSIX standard: for the default
+scheduling policy, POSIX makes no guarantees of fairness, such as "the
+thread waiting for the mutex for the longest time always acquires it
+first".  Properly written multithreaded code avoids that kind of heavy
+contention on mutexes, and does not run into fairness problems.  If
+you need scheduling guarantees, you should consider using the
+real-time scheduling policies SCHED_RR and
+SCHED_FIFO, which have precisely defined scheduling
+behaviors. 

 
 
D.7: I have a simple test program with two threads
 that do nothing but printf() in tight loops, and from the
 printout it seems that only one thread is running, the other doesn't
 print anything!

 
-If you wait long enough, you should see the second thread kick in.
-But still, you're right, one thread prevents the other one from
-running for long periods of time.  The reason is explained in
+Again, this behavior is characteristic of old releases of LinuxThreads
+(0.7 and before); more recent versions (0.8 and up) should not exhibit
+this behavior.

+
+The reason for this behavior is explained in
 question D.6 above: printf() performs
 locking on stdout, and thus your two threads contend very
 heavily for the mutex associated with stdout.  But if you
 do some real work between two calls to printf(), you'll
-see that scheduling becomes much smoother. 

+see that scheduling becomes much smoother.

 
 
D.8: I've looked at <pthread.h>
 and there seems to be a gross error in the pthread_cleanup_push
@@ -347,7 +377,7 @@ but then the POSIX guys discovered it was redundant with
 <pthread.h>.
 For instance, the second argument to pthread_create()
 should be a pthread_attr_t, not a
-pthread_attr_t *. Also, didn't you forget to declare 
+pthread_attr_t *. Also, didn't you forget to declare
 pthread_attr_default?

 
 No, I didn't.  What you're describing is draft 4 of the POSIX
@@ -402,29 +432,23 @@ threads when one thread receives the SIGSTOP signal!
 One day, LinuxThreads will implement that behavior, and the
 non-portable hack with SIGSTOP won't work anymore.

 
-
E.5: LinuxThreads does not implement
-pthread_attr_setstacksize() nor
-pthread_attr_setstackaddr().  Why? 

+
E.5: Does LinuxThreads implement
+pthread_attr_setstacksize() and
+pthread_attr_setstackaddr()?

 
-These two functions are part of optional components of the POSIX
-standard, meaning that portable applications should test for the
-"feature test" macros _POSIX_THREAD_ATTR_STACKSIZE and
-_POSIX_THREAD_ATTR_STACKADDR (respectively) before using these
-functions.

+These optional functions are provided in recent versions of
+LinuxThreads (0.8 and up).  Earlier releases did not provide these
+optional components of the POSIX standard.

 
-pthread_attr_setstacksize() lets the programmer specify
-the maximum stack size for a thread.  In LinuxThreads, stacks start
-small (4k) and grow on demand to a fairly large limit (2M), which
-cannot be modified on a per-thread basis for architectural reasons.
-Hence there is really no need to specify any stack size yourself: the
-system does the right thing all by itself.  Besides, there is no
-portable way to estimate the stack requirements of a thread, so
-setting the stack size is pretty useless anyway.

-
-pthread_attr_setstackaddr() is even more questionable: it
-lets users specify the stack location for a thread.  Again,
-LinuxThreads takes care of that for you.  Why you would ever need to
-set the stack address escapes me.

+Even if pthread_attr_setstacksize() and
+pthread_attr_setstackaddr() are now provided, we still
+recommend that you do not use them unless you really have strong
+reasons for doing so.  The default stack allocation strategy for
+LinuxThreads is nearly optimal: stacks start small (4k) and
+automatically grow on demand to a fairly large limit (2M).
+Moreover, there is no portable way to estimate the stack requirements
+of a thread, so setting the stack size yourself makes your program
+less reliable and non-portable.

 
 
E.6: LinuxThreads does not support the
 PTHREAD_SCOPE_PROCESS value of the "contentionscope"
@@ -507,54 +531,21 @@ want to use the libg++, I have a libg++ add-on for egcs.
 

 

 
-
G.  Debugging LinuxThreads programs

+
G. Debugging LinuxThreads programs

 
 
G.1: Can I debug LinuxThreads program using gdb?

 
-Essentially, no.  gdb is basically not aware of the threads.  It
-will let you debug the main thread, and also inspect the global state,
-but you won't have any control over the other threads.  Worse, you
-can't put any breakpoint anywhere in the code: if a thread other than
-the main thread hits the breakpoint, it will just crash!

+Yes, but not with the stock gdb 4.17.  You need a specially patched
+version of gdb 4.17 developed by Eric Paire and colleages at The Open
+Group, Grenoble.  The patches against gdb 4.17 are available at
+http://www.gr.opengroup.org/java/jdk/linux/debug.htm.
+Precompiled binaries of the patched gdb are available in RedHat's RPM
+format at http://odin.appliedtheory.com/.
 
-For running gdb on the main thread, you need to instruct gdb to ignore
-the signals used by LinuxThreads. Just do:
-
-        handle SIGUSR1 nostop pass noprint
-        handle SIGUSR2 nostop pass noprint
+
G.2: Does it work with post-mortem debugging?

 
-

-
-
G.2: What about attaching to a running thread using
-the attach command of gdb?

-
-For reasons I don't fully understand, this does not work.

-
-
G.3: But I know gdb supports threads on some
-platforms! Why not on Linux?

-
-You're correct that gdb has some built-in support for threads, in
-particular the IRIX "sprocs" model, which is a "one thread = one
-process" model fairly close to LinuxThreads.  But gdb under IRIX uses
-ioctls on /proc to control debugged processes, while
-under Linux it uses the traditional ptrace(). The support
-for threads is built in the /proc interface, but some
-work remains to be done to have it in the ptrace()
-interface.  In summary, it should not be impossible to get gdb to work
-with LinuxThreads, but it's definitely not trivial.
-
-
G.4: OK, I'll do post-mortem debugging, then.  But
-gdb cannot read core files generated by a multithreaded program!  Or,
-the core file is readable from gcc, but does not correspond to the
-thread that crashed!  What happens?

-
-Some versions of gdb do indeed have problems with post-mortem
-debugging in general, but this is not specific to LinuxThreads.
-Recent Linux distributions seem to have corrected this problem,
-though.

-
-Regarding the fact that the core file does not correspond to the
-thread that crashed, the reason is that the kernel will not dump core
+Not very well.  Generally, the core file does not correspond to the
+thread that crashed.  The reason is that the kernel will not dump core
 for a process that shares its memory with other processes, such as the
 other threads of your program.  So, the thread that crashes silently
 disappears without generating a core file.  Then, all other threads of
@@ -564,7 +555,7 @@ one that dies is no longer sharing its memory with anyone else, so the
 kernel generates a core file for that thread.  Unfortunately, that's
 not the thread you are interested in.
 
-
G.5: How can I debug multithreaded programs, then?

+
G.3: Any other ways to debug multithreaded programs, then?

 
 Assertions and printf() are your best friends.  Try to debug
 sequential parts in a single-threaded program first.  Then, put
@@ -572,8 +563,8 @@ sequential parts in a single-threaded program first.  Then, put
 Also, check invariants often with the assert() macro.  In truth,
 there is no other effective way (save for a full formal proof of your
 program) to track down concurrency bugs.  Debuggers are not really
-effective for concurrency problems, because they disrupt program
-execution too much.

+effective for subtle concurrency problems, because they disrupt
+program execution too much.

 
 

 

@@ -597,7 +588,7 @@ program, stdio functions require additional locking, which the macros
 don't perform, so we must call functions instead.

 
 
  •  More importantly, <errno.h> redefines errno when
-_REENTRANT is 
+_REENTRANT is
 defined, so that errno refers to the thread-specific errno location
 rather than the global errno variable.  This is achieved by the
 following #define in <errno.h>:
@@ -664,32 +655,24 @@ code concludes that it cannot handle the error and stops.
    
 
    H.4: With LinuxThreads, I can no longer use the signals
 SIGUSR1 and SIGUSR2 in my programs! Why? 
    
 
+The short answer is: because the Linux kernel you're using does not
+support realtime signals.  
    
+
 LinuxThreads needs two signals for its internal operation.
 One is used to suspend and restart threads blocked on mutex, condition
-or semaphore operations.  The other is used for thread cancellation.
-Since the only two signals not reserved for the Linux kernel are
-SIGUSR1 and SIGUSR2, LinuxThreads has no
-other choice than using them.  I know this is unfortunate, and hope
-this problem will be addressed in future Linux kernels, either by
-freeing some of the regular signals (unlikely), or by providing more
-than 32 signals (as per the POSIX 1003.1b realtime extensions).
    
+or semaphore operations.  The other is used for thread
+cancellation.
    
 
-In the meantime, you can try to use kernel-reserved signals either in
-your program or in LinuxThreads.  For instance,
-SIGSTKFLT and SIGUNUSED appear to be
-unused in the current Linux kernels for the Intel x86 architecture.
-To use these in LinuxThreads, the only file you need to change
-is internals.h, more specifically the two lines:
-
    -        #define PTHREAD_SIG_RESTART SIGUSR1
-        #define PTHREAD_SIG_CANCEL SIGUSR2
-
    
-Replace them by e.g.
-
    -        #define PTHREAD_SIG_RESTART SIGSTKFLT
-        #define PTHREAD_SIG_CANCEL SIGUNUSED
-
    
-Warning: you're doing this at your own risks.
    
+On ``old'' kernels (2.0 and early 2.1 kernels), there are only 32
+signals available and the kernel reserves all of them but two:
+SIGUSR1 and SIGUSR2.  So, LinuxThreads has
+no choice but use those two signals.
    
+
+On recent kernels (late 2.1 kernels and the forthcoming 2.2 kernels),
+more than 32 signals are provided in the form of realtime signals.
+When run on one of those kernels, LinuxThreads uses two reserved
+realtime signals for its internal operation, thus leaving
+SIGUSR1 and SIGUSR2 free for user code.
    
 
 
    H.5: Is the stack of one thread visible from the
 other threads?  Can I pass a pointer into my stack to other threads?
@@ -731,16 +714,21 @@ occurred.
    
 
    I.2: So, what can I do to build a multithreaded X
 Windows client? 
    
 
-The best solution is to recompile the X libraries with multithreading
+The best solution is to use X libraries that have been compiled with
+multithreading options set.  Linux distributions that come with glibc
+2 as the main C library generally provide thread-safe X libraries.
+At least, that seems to be the case for RedHat 5.
    
+
+You can try to recompile yourself the X libraries with multithreading
 options set.  They contain optional support for multithreading; it's
-just that all binary distributions for Linux were built without this
-support.  See the file README.Xfree3.3 in the LinuxThreads
-distribution for patches and info on how to compile thread-safe X
-libraries from the Xfree3.3 distribution.  The Xfree3.3 sources are
-readily available in most Linux distributions, e.g. as a source RPM
-for RedHat.  Be warned, however, that X Windows is a huge system, and
-recompiling even just the libraries takes a lot of time and disk
-space.
    
+just that the binaries provided by your Linux distribution were built
+without this support.  See the file README.Xfree3.3 in
+the LinuxThreads distribution for patches and info on how to compile
+thread-safe X libraries from the Xfree3.3 distribution.  The Xfree3.3
+sources are readily available in most Linux distributions, e.g. as a
+source RPM for RedHat.  Be warned, however, that X Windows is a huge
+system, and recompiling even just the libraries takes a lot of time
+and disk space.
    
 
 Another, less involving solution is to call X functions only from the
 main thread of your program.  Even if all threads have their own errno
@@ -752,9 +740,8 @@ only. 
    
 
    This is a lot of work. Don't you have precompiled
 thread-safe X libraries that you could distribute?
    
 
-No, I don't.  Sorry.  But you could approach the maintainers of
-your Linux distribution to see if they would be willing to provide
-thread-safe X libraries.
    
+No, I don't.  Sorry.  But consider installing a Linux distribution
+that comes with thread-safe X libraries, such as RedHat 5.
    
 
 
    I.3: Can I use library FOO in a multithreaded
 program?
    
@@ -786,8 +773,7 @@ execute code not compiled with -D_REENTRANT.
    
 
 
 Because both LinuxThreads and SVGAlib use the signals
-SIGUSR1 and SIGUSR2.  One of the two should
-be recompiled to use different signals.  See question SIGUSR1 and SIGUSR2.  See question H.4.
 
    
 
@@ -856,7 +842,7 @@ handled by that thread.  As long as no thread is blocking the signal,
 the behavior conforms to the standard: one (unspecified) thread of the
 program handles the signal.  But if the thread to which PID the signal
 is sent blocks the signal, and some other thread does not block the
-signal, then LinuxThreads will simply queue in 
+signal, then LinuxThreads will simply queue in
 that thread and execute the handler only when that thread unblocks
 the signal, instead of executing the handler immediately in the other
 thread that does not block the signal.
    
@@ -966,20 +952,6 @@ pretty good job of making kernel-level context switches between
 threads efficient.  LinuxThreads is just following the general
 direction they set.
    
 
-
    K.3: I looked at the LinuxThreads sources, and I saw
-quite a lot of spinlocks and busy-waiting loops to acquire these
-spinlocks.  Isn't this a big waste of CPU time?
    
-
-Look more carefully.  Spinlocks are used internally to protect
-LinuxThreads's data structures, but these locks are held for very
-short periods of time: 10 instructions or so.  The probability that a
-thread has to loop busy-waiting on a taken spinlock for more than,
-say, 100 cycles is very, very low.  When a thread needs to wait on a
-mutex, condition, or semaphore, it actually puts itself on a waiting
-queue, then suspends on a signal, consuming no CPU time at all.  The
-thread will later be restarted by sending it a signal when the state
-of the mutex, condition, or semaphore changes.
    
-
 
    
 
    Xavier.Leroy@inria.fr
    
 
diff --git a/linuxthreads/attr.c b/linuxthreads/attr.c
index 7a099857aa..3a19ddc49b 100644
--- a/linuxthreads/attr.c
+++ b/linuxthreads/attr.c
@@ -146,10 +146,8 @@ int __pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize)
   /* First round up the guard size.  */
   guardsize = roundup (guardsize, ps);
 
-  /* The current implementation of LinuxThreads allocates 2MB stack space
-     for each thread.  So the maximum guardsize is 2MB - pagesize.  */
-  if (guardsize >= STACK_SIZE - ps)
-    return EINVAL;
+  /* The guard size must not be larger than the stack itself */
+  if (guardsize >= attr->stacksize) return EINVAL;
 
   attr->guardsize = guardsize;
 
diff --git a/linuxthreads/cancel.c b/linuxthreads/cancel.c
index cd2bbace12..eda5d88154 100644
--- a/linuxthreads/cancel.c
+++ b/linuxthreads/cancel.c
@@ -61,7 +61,7 @@ int pthread_cancel(pthread_t thread)
   handle->h_descr->p_canceled = 1;
   pid = handle->h_descr->p_pid;
   __pthread_unlock(&handle->h_lock);
-  kill(pid, PTHREAD_SIG_CANCEL);
+   kill(pid, __pthread_sig_cancel);
   return 0;
 }
 
diff --git a/linuxthreads/condvar.c b/linuxthreads/condvar.c
index 91067d2d17..480a8e426e 100644
--- a/linuxthreads/condvar.c
+++ b/linuxthreads/condvar.c
@@ -86,7 +86,7 @@ pthread_cond_timedwait_relative(pthread_cond_t *cond,
     } else {
       /* Unblock the restart signal */
       sigemptyset(&unblock);
-      sigaddset(&unblock, PTHREAD_SIG_RESTART);
+      sigaddset(&unblock, __pthread_sig_restart);
       sigprocmask(SIG_UNBLOCK, &unblock, &initial_mask);
       /* Sleep for the required duration */
       retsleep = __libc_nanosleep(reltime, NULL);
diff --git a/linuxthreads/internals.h b/linuxthreads/internals.h
index d68adeb987..62c14c606d 100644
--- a/linuxthreads/internals.h
+++ b/linuxthreads/internals.h
@@ -130,16 +130,13 @@ struct pthread_request {
 
 /* Signals used for suspend/restart and for cancellation notification.  */
 
-#ifdef SIGRTMIN
-/* The have real-time signals.  */
 extern int __pthread_sig_restart;
 extern int __pthread_sig_cancel;
-# define PTHREAD_SIG_RESTART __pthread_sig_restart
-# define PTHREAD_SIG_CANCEL __pthread_sig_cancel
-#else
-# define PTHREAD_SIG_RESTART SIGUSR1
-# define PTHREAD_SIG_CANCEL SIGUSR2
-#endif
+
+/* Default signals used if we don't have realtime signals */
+
+#define DEFAULT_SIG_RESTART SIGUSR1
+#define DEFAULT_SIG_CANCEL SIGUSR2
 
 /* Global array of thread handles, used for validating a thread id
    and retrieving the corresponding thread descriptor. Also used for
diff --git a/linuxthreads/manager.c b/linuxthreads/manager.c
index d14a57ccd7..41acf01b29 100644
--- a/linuxthreads/manager.c
+++ b/linuxthreads/manager.c
@@ -23,6 +23,7 @@
 #include 
 #include 		/* for poll */
 #include            /* for mmap */
+#include 
 #include 
 #include            /* for waitpid macros */
 #include 
@@ -99,11 +100,11 @@ int __pthread_manager(void *arg)
   /* Set the error variable.  */
   __pthread_manager_thread.p_errnop = &__pthread_manager_thread.p_errno;
   __pthread_manager_thread.p_h_errnop = &__pthread_manager_thread.p_h_errno;
-  /* Block all signals except PTHREAD_SIG_RESTART, PTHREAD_SIG_CANCEL
+  /* Block all signals except __pthread_sig_restart, __pthread_sig_cancel
      and SIGTRAP */
   sigfillset(&mask);
-  sigdelset(&mask, PTHREAD_SIG_RESTART);
-  sigdelset(&mask, PTHREAD_SIG_CANCEL); /* for debugging new threads */
+  sigdelset(&mask, __pthread_sig_restart);
+  sigdelset(&mask, __pthread_sig_cancel); /* for debugging new threads */
   sigdelset(&mask, SIGTRAP);            /* for debugging purposes */
   sigprocmask(SIG_SETMASK, &mask, NULL);
   /* Raise our priority to match that of main thread */
@@ -161,7 +162,7 @@ int __pthread_manager(void *arg)
         break;
       case REQ_DEBUG:
         /* Make gdb aware of new thread */
-        if (__pthread_threads_debug) raise(PTHREAD_SIG_CANCEL);
+	if (__pthread_threads_debug) raise(__pthread_sig_cancel);
         restart(request.req_thread);
         break;
       }
@@ -205,6 +206,78 @@ static int pthread_start_thread(void *arg)
   return 0;
 }
 
+static int pthread_allocate_stack(const pthread_attr_t *attr,
+                                  pthread_descr default_new_thread,
+                                  int pagesize,
+                                  pthread_descr * out_new_thread,
+                                  char ** out_new_thread_bottom,
+                                  char ** out_guardaddr,
+                                  size_t * out_guardsize)
+{
+  pthread_descr new_thread;
+  char * new_thread_bottom;
+  char * guardaddr;
+  size_t stacksize, guardsize;
+
+  if (attr != NULL && attr->stackaddr_set)
+    {
+      /* The user provided a stack. */
+      new_thread =
+        (pthread_descr) ((long)(attr->stackaddr) & -sizeof(void *)) - 1;
+      new_thread_bottom = (char *) attr->stackaddr - attr->stacksize;
+      guardaddr = NULL;
+      guardsize = 0;
+    }
+  else
+    {
+      /* Allocate space for stack and thread descriptor at default address */
+      new_thread = default_new_thread;
+      new_thread_bottom = (char *) new_thread - STACK_SIZE;
+      if (mmap((caddr_t)((char *)(new_thread + 1) - INITIAL_STACK_SIZE),
+               INITIAL_STACK_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC,
+               MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED | MAP_GROWSDOWN,
+               -1, 0) == MAP_FAILED)
+        /* Bad luck, this segment is already mapped. */
+        return -1;
+      /* We manage to get a stack.  Now see whether we need a guard
+         and allocate it if necessary.  Notice that the default
+         attributes (stack_size = STACK_SIZE - pagesize and
+         guardsize = pagesize) do not need a guard page, since
+         the RLIMIT_STACK soft limit prevents stacks from
+         running into one another. */
+      if (attr == NULL ||
+          attr->guardsize == 0 ||
+          (attr->guardsize == pagesize &&
+           attr->stacksize == STACK_SIZE - pagesize))
+        {
+          /* We don't need a guard page. */
+          guardaddr = NULL;
+          guardsize = 0;
+        }
+      else
+        {
+          /* Put a bad page at the bottom of the stack */
+          stacksize = roundup(attr->stacksize, pagesize);
+          if (stacksize >= STACK_SIZE - pagesize)
+            stacksize = STACK_SIZE - pagesize;
+          guardaddr = (void *)new_thread - stacksize;
+          guardsize = attr->guardsize;
+          if (mmap ((caddr_t) guardaddr, guardsize, 0, MAP_FIXED, -1, 0)
+              == MAP_FAILED)
+            {
+              /* We don't make this an error.  */
+              guardaddr = NULL;
+              guardsize = 0;
+            }
+        }
+    }
+  *out_new_thread = new_thread;
+  *out_new_thread_bottom = new_thread_bottom;
+  *out_guardaddr = guardaddr;
+  *out_guardsize = guardsize;
+  return 0;
+}
+
 static int pthread_handle_create(pthread_t *thread, const pthread_attr_t *attr,
 				 void * (*start_routine)(void *), void *arg,
 				 sigset_t * mask, int father_pid)
@@ -214,8 +287,9 @@ static int pthread_handle_create(pthread_t *thread, const pthread_attr_t *attr,
   pthread_descr new_thread;
   char * new_thread_bottom;
   pthread_t new_thread_id;
-  void *guardaddr = NULL;
+  char *guardaddr = NULL;
   size_t guardsize = 0;
+  int pagesize = __getpagesize();
 
   /* First check whether we have to change the policy and if yes, whether
      we can  do this.  Normally this should be done by examining the
@@ -223,50 +297,17 @@ static int pthread_handle_create(pthread_t *thread, const pthread_attr_t *attr,
      but this is hard to implement.  FIXME  */
   if (attr != NULL && attr->schedpolicy != SCHED_OTHER && geteuid () != 0)
     return EPERM;
-  /* Find a free stack segment for the current stack */
+  /* Find a free segment for the thread, and allocate a stack if needed */
   for (sseg = 1; ; sseg++)
     {
       if (sseg >= PTHREAD_THREADS_MAX)
 	return EAGAIN;
       if (__pthread_handles[sseg].h_descr != NULL)
 	continue;
-
-      if (attr == NULL || !attr->stackaddr_set)
-	{
-	  new_thread = thread_segment(sseg);
-	  new_thread_bottom = (char *) new_thread - STACK_SIZE;
-	  /* Allocate space for stack and thread descriptor. */
-	  if (mmap((caddr_t)((char *)(new_thread+1) - INITIAL_STACK_SIZE),
-		   INITIAL_STACK_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC,
-		   MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED | MAP_GROWSDOWN,
-		   -1, 0) != MAP_FAILED)
-	    {
-	      /* We manage to get a stack.  Now see whether we need a guard
-		 and allocate it if necessary.  */
-	      if (attr == NULL || attr->guardsize != 0)
-		{
-		  guardsize = attr ? attr->guardsize : __getpagesize ();
-		  guardaddr = mmap ((caddr_t)((char *)(new_thread+1)
-					      - STACK_SIZE),
-				    guardsize, 0, MAP_FIXED, -1, 0);
-		  if (guardaddr == MAP_FAILED)
-		    {
-		      /* We don't make this an error.  */
-		      guardaddr = NULL;
-		      guardsize = 0;
-		    }
-		}
-	      break;
-	    }
-	  /* It seems part of this segment is already mapped. Try the next. */
-	}
-      else
-	{
-	  new_thread = (pthread_descr) ((long) attr->stackaddr
-					& -sizeof(void *)) - 1;
-	  new_thread_bottom = (char *) attr->stackaddr - attr->stacksize;
-	  break;
-	}
+      if (pthread_allocate_stack(attr, thread_segment(sseg), pagesize,
+                                 &new_thread, &new_thread_bottom,
+                                 &guardaddr, &guardsize) == 0)
+        break;
     }
   /* Allocate new thread identifier */
   pthread_threads_counter += PTHREAD_THREADS_MAX;
@@ -329,7 +370,7 @@ static int pthread_handle_create(pthread_t *thread, const pthread_attr_t *attr,
   /* Do the cloning */
   pid = __clone(pthread_start_thread, (void **) new_thread,
                 CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND |
-                PTHREAD_SIG_RESTART,
+                __pthread_sig_restart,
                 new_thread);
   /* Check if cloning succeeded */
   if (pid == -1) {
@@ -492,7 +533,7 @@ static void pthread_handle_exit(pthread_descr issuing_thread, int exitcode)
   for (th = issuing_thread->p_nextlive;
        th != issuing_thread;
        th = th->p_nextlive) {
-    kill(th->p_pid, PTHREAD_SIG_CANCEL);
+    kill(th->p_pid, __pthread_sig_cancel);
   }
   /* Now, wait for all these threads, so that they don't become zombies
      and their times are properly added to the thread manager's times. */
@@ -505,7 +546,7 @@ static void pthread_handle_exit(pthread_descr issuing_thread, int exitcode)
   _exit(0);
 }
 
-/* Handler for PTHREAD_SIG_RESTART in thread manager thread */
+/* Handler for __pthread_sig_restart in thread manager thread */
 
 void __pthread_manager_sighandler(int sig)
 {
diff --git a/linuxthreads/pthread.c b/linuxthreads/pthread.c
index a7511f7eee..313220e7a0 100644
--- a/linuxthreads/pthread.c
+++ b/linuxthreads/pthread.c
@@ -22,6 +22,7 @@
 #include 
 #include 
 #include 
+#include 
 #include "pthread.h"
 #include "internals.h"
 #include "spinlock.h"
@@ -134,8 +135,8 @@ const int __pthread_offsetof_pid = offsetof(struct _pthread_descr_struct,
                                             p_pid);
 
 /* Signal numbers used for the communication.  */
-int __pthread_sig_restart;
-int __pthread_sig_cancel;
+int __pthread_sig_restart = DEFAULT_SIG_RESTART;
+int __pthread_sig_cancel = DEFAULT_SIG_CANCEL;
 
 /* These variables are used by the setup code.  */
 extern int _errno;
@@ -149,7 +150,7 @@ static void pthread_handle_sigrestart(int sig);
 
 /* Initialize the pthread library.
    Initialization is split in two functions:
-   - a constructor function that blocks the PTHREAD_SIG_RESTART signal
+   - a constructor function that blocks the __pthread_sig_restart signal
      (must do this very early, since the program could capture the signal
       mask with e.g. sigsetjmp before creating the first thread);
    - a regular function called from pthread_create when needed. */
@@ -160,6 +161,8 @@ static void pthread_initialize(void)
 {
   struct sigaction sa;
   sigset_t mask;
+  struct rlimit limit;
+  int max_stack;
 
   /* If already done (e.g. by a constructor called earlier!), bail out */
   if (__pthread_initial_thread_bos != NULL) return;
@@ -172,6 +175,15 @@ static void pthread_initialize(void)
      STACK_SIZE boundary. */
   __pthread_initial_thread_bos =
     (char *)(((long)CURRENT_STACK_FRAME - 2 * STACK_SIZE) & ~(STACK_SIZE - 1));
+  /* Play with the stack size limit to make sure that no stack ever grows
+     beyond STACK_SIZE minus two pages (one page for the thread descriptor
+     immediately beyond, and one page to act as a guard page). */
+  getrlimit(RLIMIT_STACK, &limit);
+  max_stack = STACK_SIZE - 2 * __getpagesize();
+  if (limit.rlim_cur > max_stack) {
+    limit.rlim_cur = max_stack;
+    setrlimit(RLIMIT_STACK, &limit);
+  }
   /* Update the descriptor for the initial thread. */
   __pthread_initial_thread.p_pid = __getpid();
   /* If we have special thread_self processing, initialize that for the
@@ -190,8 +202,8 @@ static void pthread_initialize(void)
     {
       /* The kernel does not support real-time signals.  Use as before
 	 the available signals in the fixed set.  */
-      __pthread_sig_restart = SIGUSR1;
-      __pthread_sig_cancel = SIGUSR2;
+      __pthread_sig_restart = DEFAULT_SIG_RESTART;
+      __pthread_sig_cancel = DEFAULT_SIG_CANCEL;
     }
 #endif
   /* Setup signal handlers for the initial thread.
@@ -201,14 +213,14 @@ static void pthread_initialize(void)
   sigemptyset(&sa.sa_mask);
   sa.sa_flags = SA_RESTART; /* does not matter for regular threads, but
                                better for the thread manager */
-  __sigaction(PTHREAD_SIG_RESTART, &sa, NULL);
+  __sigaction(__pthread_sig_restart, &sa, NULL);
   sa.sa_handler = pthread_handle_sigcancel;
   sa.sa_flags = 0;
-  __sigaction(PTHREAD_SIG_CANCEL, &sa, NULL);
+  __sigaction(__pthread_sig_cancel, &sa, NULL);
 
-  /* Initially, block PTHREAD_SIG_RESTART. Will be unblocked on demand. */
+  /* Initially, block __pthread_sig_restart. Will be unblocked on demand. */
   sigemptyset(&mask);
-  sigaddset(&mask, PTHREAD_SIG_RESTART);
+  sigaddset(&mask, __pthread_sig_restart);
   sigprocmask(SIG_BLOCK, &mask, NULL);
   /* Register an exit function to kill all other threads. */
   /* Do it early so that user-registered atexit functions are called
@@ -254,7 +266,7 @@ int __pthread_initialize_manager(void)
   __pthread_manager_reader = manager_pipe[0]; /* reading end */
   __pthread_manager_thread.p_pid = pid;
   /* Make gdb aware of new thread manager */
-  if (__pthread_threads_debug) raise(PTHREAD_SIG_CANCEL);
+  if (__pthread_threads_debug) raise(__pthread_sig_cancel);
   /* Synchronize debugging of the thread manager */
   request.req_kind = REQ_DEBUG;
   __libc_write(__pthread_manager_request, (char *) &request, sizeof(request));
@@ -433,7 +445,7 @@ static void pthread_handle_sigrestart(int sig)
    The debugging strategy is as follows:
    On reception of a REQ_DEBUG request (sent by new threads created to
    the thread manager under debugging mode), the thread manager throws
-   PTHREAD_SIG_CANCEL to itself. The debugger (if active) intercepts
+   __pthread_sig_cancel to itself. The debugger (if active) intercepts
    this signal, takes into account new threads and continue execution
    of the thread manager by propagating the signal because it doesn't
    know what it is specifically done for. In the current implementation,
diff --git a/linuxthreads/restart.h b/linuxthreads/restart.h
index 4b4a1d7937..54a6f50321 100644
--- a/linuxthreads/restart.h
+++ b/linuxthreads/restart.h
@@ -18,7 +18,7 @@
 
 static inline void restart(pthread_descr th)
 {
-  kill(th->p_pid, PTHREAD_SIG_RESTART);
+  kill(th->p_pid, __pthread_sig_restart);
 }
 
 static inline void suspend(pthread_descr self)
@@ -26,11 +26,11 @@ static inline void suspend(pthread_descr self)
   sigset_t mask;
 
   sigprocmask(SIG_SETMASK, NULL, &mask); /* Get current signal mask */
-  sigdelset(&mask, PTHREAD_SIG_RESTART); /* Unblock the restart signal */
+  sigdelset(&mask, __pthread_sig_restart); /* Unblock the restart signal */
   do {
     self->p_signal = 0;
     sigsuspend(&mask);                   /* Wait for signal */
-  } while (self->p_signal != PTHREAD_SIG_RESTART);
+  } while (self->p_signal !=__pthread_sig_restart );
 }
 
 static inline void suspend_with_cancellation(pthread_descr self)
@@ -39,7 +39,7 @@ static inline void suspend_with_cancellation(pthread_descr self)
   sigjmp_buf jmpbuf;
 
   sigprocmask(SIG_SETMASK, NULL, &mask); /* Get current signal mask */
-  sigdelset(&mask, PTHREAD_SIG_RESTART); /* Unblock the restart signal */
+  sigdelset(&mask, __pthread_sig_restart); /* Unblock the restart signal */
   /* No need to save the signal mask, we'll restore it ourselves */
   if (sigsetjmp(jmpbuf, 0) == 0) {
     self->p_cancel_jmp = &jmpbuf;
@@ -47,11 +47,11 @@ static inline void suspend_with_cancellation(pthread_descr self)
       do {
 	self->p_signal = 0;
         sigsuspend(&mask);               /* Wait for a signal */
-      } while (self->p_signal != PTHREAD_SIG_RESTART);
+      } while (self->p_signal != __pthread_sig_restart);
     }
     self->p_cancel_jmp = NULL;
   } else {
-    sigaddset(&mask, PTHREAD_SIG_RESTART); /* Reblock the restart signal */
+    sigaddset(&mask, __pthread_sig_restart); /* Reblock the restart signal */
     sigprocmask(SIG_SETMASK, &mask, NULL);
   }
 }
diff --git a/linuxthreads/signals.c b/linuxthreads/signals.c
index 4a83b14d83..ac752d145a 100644
--- a/linuxthreads/signals.c
+++ b/linuxthreads/signals.c
@@ -26,18 +26,18 @@ int pthread_sigmask(int how, const sigset_t * newmask, sigset_t * oldmask)
 
   if (newmask != NULL) {
     mask = *newmask;
-    /* Don't allow PTHREAD_SIG_RESTART to be unmasked.
-       Don't allow PTHREAD_SIG_CANCEL to be masked. */
+    /* Don't allow __pthread_sig_restart to be unmasked.
+       Don't allow __pthread_sig_cancel to be masked. */
     switch(how) {
     case SIG_SETMASK:
-      sigaddset(&mask, PTHREAD_SIG_RESTART);
-      sigdelset(&mask, PTHREAD_SIG_CANCEL);
+      sigaddset(&mask, __pthread_sig_restart);
+      sigdelset(&mask, __pthread_sig_cancel);
       break;
     case SIG_BLOCK:
-      sigdelset(&mask, PTHREAD_SIG_CANCEL);
+      sigdelset(&mask, __pthread_sig_cancel);
       break;
     case SIG_UNBLOCK:
-      sigdelset(&mask, PTHREAD_SIG_RESTART);
+      sigdelset(&mask, __pthread_sig_restart);
       break;
     }
     newmask = &mask;
@@ -94,7 +94,7 @@ int sigaction(int sig, const struct sigaction * act,
 {
   struct sigaction newact;
 
-  if (sig == PTHREAD_SIG_RESTART || sig == PTHREAD_SIG_CANCEL)
+  if (sig == __pthread_sig_restart || sig == __pthread_sig_cancel)
     return EINVAL;
   newact = *act;
   if (act->sa_handler != SIG_IGN && act->sa_handler != SIG_DFL)
@@ -116,9 +116,9 @@ int sigwait(const sigset_t * set, int * sig)
   /* Get ready to block all signals except those in set
      and the cancellation signal */
   sigfillset(&mask);
-  sigdelset(&mask, PTHREAD_SIG_CANCEL);
+  sigdelset(&mask, __pthread_sig_cancel);
   for (s = 1; s <= NSIG; s++) {
-    if (sigismember(set, s) && s != PTHREAD_SIG_CANCEL)
+    if (sigismember(set, s) && s != __pthread_sig_cancel)
       sigdelset(&mask, s);
   }
   /* Test for cancellation */
diff --git a/sysdeps/mach/hurd/dl-sysdep.c b/sysdeps/mach/hurd/dl-sysdep.c
index abaf0b2676..2495af4de9 100644
--- a/sysdeps/mach/hurd/dl-sysdep.c
+++ b/sysdeps/mach/hurd/dl-sysdep.c
@@ -500,6 +500,18 @@ __libc_read (int fd, void *buf, size_t nbytes)
   return nread;
 }
 
+off_t weak_function
+__lseek (int fd, off_t offset, int whence)
+{
+  error_t err;
+  
+  err = __io_seek ((mach_port_t) fd, offset, whence, &offset);
+  if (err)
+    return __hurd_fail (err);
+  
+  return offset;
+}
+
 __ptr_t weak_function
 __mmap (__ptr_t addr, size_t len, int prot, int flags, int fd, off_t offset)
 {
@@ -570,7 +582,6 @@ __fxstat (int vers, int fd, struct stat *buf)
     return __hurd_fail (err);
 
   return 0;
-  
 }
 
 int weak_function
@@ -590,6 +601,19 @@ __xstat (int vers, const char *file, struct stat *buf)
   return 0;
 }
 
+pid_t weak_function
+__getpid ()
+{
+  pid_t pid, ppid;
+  int orphaned;
+  
+  if (__proc_getpids (_dl_hurd_data->portarray[INIT_PORT_PROC],
+		      &pid, &ppid, &orphaned))
+    return -1;
+
+  return pid;
+}
+
 void weak_function
 _exit (int status)
 {
@@ -598,6 +622,29 @@ _exit (int status)
   while (__task_terminate (__mach_task_self ()))
     __mach_task_self_ = (__mach_task_self) ();
 }
+
+/* Try to get a machine dependent instruction which will make the
+   program crash.  This is used in case everything else fails.  */
+#include 
+#ifndef ABORT_INSTRUCTION
+/* No such instruction is available.  */
+# define ABORT_INSTRUCTION
+#endif
+
+void weak_function
+abort (void)
+{
+  /* Try to abort using the system specific command.  */
+  ABORT_INSTRUCTION;
+
+  /* If the abort instruction failed, exit.  */
+  _exit (127);
+
+  /* If even this fails, make sure we never return.  */
+  while (1)
+    /* Try for ever and ever.  */
+    ABORT_INSTRUCTION;
+}
 
 /* This function is called by interruptible RPC stubs.  For initial
    dynamic linking, just use the normal mach_msg.  Since this defn is