Update the thread stack base when `scm_with_guile' is invoked multiple times.

* NEWS: Update.

* libguile/threads.c (scm_i_init_thread_for_guile): When the thread is
  already guilified, update `t->base' so that it corresponds to the new
  stack base.  Bug report and patch by Linas Vepstas <linasvepstas@gmail.com>.

* test-suite/standalone/Makefile.am (test_scm_with_guile_CFLAGS,
  test_scm_with_guile_LDADD): New.
  (check_PROGRAMS, TESTS): Add `test-scm-with-guile'.

NEWS

@@ -41,6 +41,8 @@ available: Guile is now always configured in "maintainer mode".
 ** Fix build failure on Debian hppa architecture (bad stack growth detection)
 ** Fix `gcd' when called with a single, negative argument.
 ** Fix `Stack overflow' errors seen when building on some platforms
+** Fix bug when `scm_with_guile ()' was called several times from the
+   same thread
 
 
 Changes in 1.8.5 (since 1.8.4)

libguile/threads.c

@@ -594,9 +594,18 @@ scm_i_init_thread_for_guile (SCM_STACKITEM *base, SCM parent)
       /* This thread is already guilified but not in guile mode, just
 	 resume it.
 
-	 XXX - base might be lower than when this thread was first
-	 guilified.
-       */
+         A user call to scm_with_guile() will lead us to here.  This could
+         happen from anywhere on the stack, and in particular lower on the
+         stack than when it was when this thread was first guilified.  Thus,
+         `base' must be updated.  */
+#if SCM_STACK_GROWS_UP
+      if (base < t->base)
+         t->base = base;
+#else
+      if (base > t->base)
+         t->base = base;
+#endif
+
       scm_enter_guile ((scm_t_guile_ticket) t);
       return 1;
     }

test-suite/standalone/.gitignore

@@ -6,3 +6,4 @@
 /test-unwind
 /test-with-guile-module
 /test-use-srfi
+/test-scm-with-guile

test-suite/standalone/Makefile.am

@@ -121,9 +121,14 @@ test_with_guile_module_LDADD = ${top_builddir}/libguile/libguile.la
 check_PROGRAMS += test-with-guile-module
 TESTS += test-with-guile-module
 
+test_scm_with_guile_CFLAGS = ${test_cflags}
+test_scm_with_guile_LDADD = ${top_builddir}/libguile/libguile.la
+check_PROGRAMS += test-scm-with-guile
+TESTS += test-scm-with-guile
+
 else
 
-EXTRA_DIST += test-with-guile-module.c
+EXTRA_DIST += test-with-guile-module.c test-scm-with-guile.c
 
 endif
 

test-suite/standalone/test-scm-with-guile.c

@@ -0,0 +1,66 @@
+/* Copyright (C) 2008 Free Software Foundation, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+
+/* Test whether `scm_with_guile ()' can be called several times from a given
+   thread, but from a different stack depth.  Up to 1.8.5, `scm_with_guile
+   ()' would not update the thread's `base' field, which would then confuse
+   the GC.
+
+   See http://lists.gnu.org/archive/html/guile-devel/2008-11/msg00037.html
+   for a detailed report.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include <libguile.h>
+
+static void *
+entry_point (void *arg)
+{
+  /* Invoke the GC.  If `THREAD->base' is incorrect, then Guile will just
+     segfault somewhere in `scm_mark_locations ()'.  */
+  scm_gc ();
+
+  return NULL;
+}
+
+static void
+go_deeper_into_the_stack (unsigned level)
+{
+  /* The assumption is that the compiler is not smart enough to optimize this
+     out.  */
+  if (level > 0)
+    go_deeper_into_the_stack (level - 1);
+  else
+    scm_with_guile (entry_point, NULL);
+}
+
+
+int
+main (int argc, char *argv[])
+{
+  /* Invoke `scm_with_guile ()' from someplace deep into the stack.  */
+  go_deeper_into_the_stack (100);
+
+  /* Invoke it from much higher into the stack.  This time, Guile is expected
+     to update the `base' field of the current thread.  */
+  scm_with_guile (entry_point, NULL);
+
+  return 0;
+}