Port to GNU/Linux HPPA malloc

On this platform, you cannot reliably malloc objects containing
values of type pthread_mutex_t or pthread_cond_t, since malloc
guarantees only 8-byte alignment but these two types require
16-byte alignment.  See GCC bug 115750
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115750> reported by
Sam James and Emacs bug 79936 <https://bugs.gnu.org/79936>
reported by John Paul Adrian Glaubitz.
* configure.ac (ALIGNOF_MAX_ALIGN_T, ALIGNOF_PTHREAD_COND_T)
(ALIGNOF_PTHREAD_MUTEX_T) [HAVE_PTHREAD]: New C macros.
* src/systhread.c (sys_mutex_init, sys_mutex_lock)
(sys_mutex_unlock, sys_cond_init, sys_cond_wait)
(sys_cond_signal, sys_cond_broadcast, sys_cond_destroy):
Use SYTHREAD_ALIGN_PTR to convert sys_mutex_t and sys_cond_t to
pthread_mutex_t and pthread_cond_t, since runtime conversion is
needed on GNU/Linux HPPA.
* src/systhread.h (SYSTHREAD_ALIGN_ROOM, SYSTHREAD_ALIGN_PTR):
New macros, which affect the generated code only on
unusual platforms like GNU/Linux HPPA.
(sys_mutex_t, sys_cond_t) [HAVE_PTHREAD]: Use them.

configure.ac

@@ -3425,6 +3425,12 @@ if test "$ac_cv_header_pthread_h" && test "$opsys" != "mingw32"; then
      done])
   if test "$emacs_cv_pthread_lib" != no; then
     AC_DEFINE([HAVE_PTHREAD], [1], [Define to 1 if you have POSIX threads.])
+    m4_foreach([emacs_type],
+      [[max_align_t], [pthread_cond_t], [pthread_mutex_t]],
+      [AC_CHECK_ALIGNOF(emacs_type,
+	 [[#include <stddef.h>
+	   #include <pthread.h>
+	 ]])])
     case $emacs_cv_pthread_lib in
       -*) LIB_PTHREAD=$emacs_cv_pthread_lib;;
     esac

src/systhread.c

@@ -106,8 +106,9 @@ sys_thread_yield (void)
 #include <sched.h>
 
 void
-sys_mutex_init (sys_mutex_t *mutex)
+sys_mutex_init (sys_mutex_t *sys_mutex)
 {
+  pthread_mutex_t *mutex = SYSTHREAD_ALIGN_PTR (pthread_mutex_t, sys_mutex);
   pthread_mutexattr_t *attr_ptr;
 #ifdef ENABLE_CHECKING
   pthread_mutexattr_t attr;
@@ -135,22 +136,25 @@ sys_mutex_init (sys_mutex_t *mutex)
 }
 
 void
-sys_mutex_lock (sys_mutex_t *mutex)
+sys_mutex_lock (sys_mutex_t *sys_mutex)
 {
+  pthread_mutex_t *mutex = SYSTHREAD_ALIGN_PTR (pthread_mutex_t, sys_mutex);
   int error = pthread_mutex_lock (mutex);
   eassert (error == 0);
 }
 
 void
-sys_mutex_unlock (sys_mutex_t *mutex)
+sys_mutex_unlock (sys_mutex_t *sys_mutex)
 {
+  pthread_mutex_t *mutex = SYSTHREAD_ALIGN_PTR (pthread_mutex_t, sys_mutex);
   int error = pthread_mutex_unlock (mutex);
   eassert (error == 0);
 }
 
 void
-sys_cond_init (sys_cond_t *cond)
+sys_cond_init (sys_cond_t *sys_cond)
 {
+  pthread_cond_t *cond = SYSTHREAD_ALIGN_PTR (pthread_cond_t, sys_cond);
   int error = pthread_cond_init (cond, NULL);
   /* We could get ENOMEM.  Can't do anything except aborting.  */
   if (error != 0)
@@ -161,22 +165,26 @@ sys_cond_init (sys_cond_t *cond)
 }
 
 void
-sys_cond_wait (sys_cond_t *cond, sys_mutex_t *mutex)
+sys_cond_wait (sys_cond_t *sys_cond, sys_mutex_t *sys_mutex)
 {
+  pthread_cond_t *cond = SYSTHREAD_ALIGN_PTR (pthread_cond_t, sys_cond);
+  pthread_mutex_t *mutex = SYSTHREAD_ALIGN_PTR (pthread_mutex_t, sys_mutex);
   int error = pthread_cond_wait (cond, mutex);
   eassert (error == 0);
 }
 
 void
-sys_cond_signal (sys_cond_t *cond)
+sys_cond_signal (sys_cond_t *sys_cond)
 {
+  pthread_cond_t *cond = SYSTHREAD_ALIGN_PTR (pthread_cond_t, sys_cond);
   int error = pthread_cond_signal (cond);
   eassert (error == 0);
 }
 
 void
-sys_cond_broadcast (sys_cond_t *cond)
+sys_cond_broadcast (sys_cond_t *sys_cond)
 {
+  pthread_cond_t *cond = SYSTHREAD_ALIGN_PTR (pthread_cond_t, sys_cond);
   int error = pthread_cond_broadcast (cond);
   eassert (error == 0);
 #ifdef HAVE_NS
@@ -189,8 +197,9 @@ sys_cond_broadcast (sys_cond_t *cond)
 }
 
 void
-sys_cond_destroy (sys_cond_t *cond)
+sys_cond_destroy (sys_cond_t *sys_cond)
 {
+  pthread_cond_t *cond = SYSTHREAD_ALIGN_PTR (pthread_cond_t, sys_cond);
   int error = pthread_cond_destroy (cond);
   eassert (error == 0);
 }

src/systhread.h

@@ -27,11 +27,45 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 
 #include <pthread.h>
 
-/* A system mutex is just a pthread mutex.  This is only used for the
+/* Deal with platforms like GNU/Linux on 32-bit HPPA, where pthread_mutex_t
-   GIL.  */
+   and pthread_cond_t have alignments stricter than what malloc guarantees.
-typedef pthread_mutex_t sys_mutex_t;
+   Unfortunately POSIX allows this curious situation.
+   Do this by allocating possibly-poorly-aligned objects a bit larger
+   than pthread_mutex_t and pthread_cond_t, and then aligning pointers
+   to these objects at runtime.  */
 
+#if (ALIGNOF_PTHREAD_COND_T <= ALIGNOF_MAX_ALIGN_T \
+     && ALIGNOF_PTHREAD_MUTEX_T <= ALIGNOF_MAX_ALIGN_T)
+/* The typical case.  Align PTR for TYPE *, where PTR is of type TYPE *
+   and is already aligned properly.  */
+# define SYSTHREAD_ALIGN_PTR(type, ptr) (ptr)
+#else
+/* An unusual case, e.g., GNU/Linux 32-bit HPPA.
+   Aligning SYSTHREAD_ALIGN_ROOM (TYPE) * up for TYPE * results in a
+   valid pointer.  TYPE's alignment must be at least that of int;
+   in practice it is always greater than that of max_align_t.  */
+# define SYSTHREAD_ALIGN_ROOM(type) \
+    union { int i; char room[sizeof (type) + alignof (type) - alignof (int)]; }
+/* Align PTR up for TYPE *.
+   PTR should be of type SYSTHREAD_ALIGN_ROOM (TYPE) *.  */
+# define SYSTHREAD_ALIGN_PTR(type, ptr) \
+    ((type *) ((uintptr_t) ((ptr)->room  + (alignof (type) - alignof (int))) \
+	       & ~(alignof (type) - alignof (int))))
+#endif
+
+/* A system mutex is just a pthread mutex, possibly with alignment slop.
+   It is used only for the GIL.  */
+#if ALIGNOF_PTHREAD_MUTEX_T <= ALIGNOF_MAX_ALIGN_T
+typedef pthread_mutex_t sys_mutex_t;
+#else
+typedef SYSTHREAD_ALIGN_ROOM (pthread_mutex_t) sys_mutex_t;
+#endif
+
+#if ALIGNOF_PTHREAD_COND_T <= ALIGNOF_MAX_ALIGN_T
 typedef pthread_cond_t sys_cond_t;
+#else
+typedef SYSTHREAD_ALIGN_ROOM (pthread_cond_t) sys_cond_t;
+#endif
 
 /* A system thread.  */
 typedef pthread_t sys_thread_t;