OpenBSD: another approach to finding stack bounds

OpenBSD provides pthread_stackseg_np(), which directly reports
the stack-bounds information that Racket needs, so we can use
that instead of the approach used on other Unix variants. The
approach used for other Unix variants seems not to work for OpenBSD
because the stack location at the point that main() is called
is already significantly far from the stack base (on the order
of 100k on a 32-bit system in my test using OpenBSD 5.2).

racket/src/racket/sconfig.h

@@ -322,15 +322,12 @@
 # endif
 
 # include <sys/param.h>
-# if OpenBSD < 201211
-/* This is needed for (pre-5.2) userspace threads: */
-#  define ASSUME_FIXED_STACK_SIZE
-#  define FIXED_STACK_SIZE 1048576
-# endif
 
 # include "uconfig.h"
 # undef HAS_STANDARD_IOB
 # define HAS_BSD_IOB
+# undef UNIX_FIND_STACK_BOUNDS
+# define PTHREAD_STACKSEG_FIND_STACK_BOUNDS
 
 /* Default UNIX_STACK_MAXIMUM is too big for a non-root user. */
 # undef UNIX_STACK_MAXIMUM
@@ -1515,6 +1512,8 @@
      line.
     ASSUME_FIXED_STACK_SIZE assumes that the main stack size is
      always FIXED_STACK_SIZE.
+    PTHREAD_STACKSEG_FIND_STACK_BOUNDS finds stack bounds using
+     pthread_stackseg_np().
     Use only one of these if DO_STACK_CHECK is used, or none otherwise. */
 
  /* FIXED_STACK_SIZE <X> sets the stack size to <X> when the

racket/src/racket/src/eval.c

@@ -144,6 +144,11 @@
 #include <sys/time.h>
 #include <sys/resource.h>
 #endif
+#ifdef PTHREAD_STACKSEG_FIND_STACK_BOUNDS
+# include <sys/signal.h>
+# include <pthread.h>
+# include <pthread_np.h>
+#endif
 #ifdef WINDOWS_FIND_STACK_BOUNDS
 #include <windows.h>
 #endif
@@ -595,9 +600,6 @@ void scheme_init_stack_check()
 {
   int *v, stack_grows_up;
   uintptr_t deeper;
-#ifdef UNIX_FIND_STACK_BOUNDS
-  struct rlimit rl;
-#endif
   
   deeper = scheme_get_deeper_address();
   stack_grows_up = (deeper > (uintptr_t)&v);
@@ -665,12 +667,14 @@ void scheme_init_stack_check()
 # endif
 
 # ifdef UNIX_FIND_STACK_BOUNDS
-    getrlimit(RLIMIT_STACK, &rl);
-  
     {
+      struct rlimit rl;
       uintptr_t bnd, lim;
+
       bnd = (uintptr_t)scheme_get_current_os_thread_stack_base();
 
+      getrlimit(RLIMIT_STACK, &rl);
+
 #  ifdef LINUX_FIND_STACK_BASE
       bnd = adjust_stack_base(bnd);
 #  endif
@@ -689,6 +693,14 @@ void scheme_init_stack_check()
       scheme_stack_boundary = bnd;
     }
 # endif
+
+# ifdef PTHREAD_STACKSEG_FIND_STACK_BOUNDS
+    {
+      stack_t stack;
+      pthread_stackseg_np(pthread_self(), &stack);
+      scheme_stack_boundary = (uintptr_t)((char *)stack.ss_sp - (stack.ss_size - STACK_SAFETY_MARGIN));
+    }
+# endif
   }
 #endif
 

racket/src/racket/src/module.c

@@ -28,7 +28,7 @@
 #include "schmach.h"
 #include "schexpobs.h"
 
-#define MIN(l,o) ((l) < (o) ? (l) : (o))
+#define mz_MIN(l,o) ((l) < (o) ? (l) : (o))
 
 /* globals */
 SHARED_OK Scheme_Object *(*scheme_module_demand_hook)(int, Scheme_Object **);
@@ -3673,7 +3673,7 @@ int scheme_resolved_module_path_value_matches(Scheme_Object *rmp, Scheme_Object
   else if (SCHEME_BYTE_STRINGP(rmp_val) && SCHEME_SYMBOLP(o)) {
     return !strncmp(SCHEME_BYTE_STR_VAL(rmp_val), 
                     SCHEME_SYM_VAL(o), 
-                    MIN(SCHEME_BYTE_STRLEN_VAL(rmp_val), SCHEME_SYM_LEN(o)));
+                    mz_MIN(SCHEME_BYTE_STRLEN_VAL(rmp_val), SCHEME_SYM_LEN(o)));
   }  else {
     scheme_arg_mismatch("scheme_resolved_module_path_value_matches", 
                         "internal error: unknown type of resolved_module_path_value",

racket/src/racket/src/mzstkchk.h

@@ -21,7 +21,7 @@
 # if defined(UNIX_FIND_STACK_BOUNDS) || defined(WINDOWS_FIND_STACK_BOUNDS) \
      || defined(MACOS_FIND_STACK_BOUNDS) || defined(ASSUME_FIXED_STACK_SIZE) \
      || defined(BEOS_FIND_STACK_BOUNDS) || defined(OSKIT_FIXED_STACK_BOUNDS) \
-     || defined(PALM_FIND_STACK_BOUNDS)
+     || defined(PALM_FIND_STACK_BOUNDS) || defined(PTHREAD_STACKSEG_FIND_STACK_BOUNDS)
   uintptr_t _stk_pos;
 
   _stk_pos = (uintptr_t)&_stk_pos;

racket/src/racket/src/schpriv.h

@@ -1705,7 +1705,7 @@ typedef struct Scheme_Overflow {
 #if defined(UNIX_FIND_STACK_BOUNDS) || defined(WINDOWS_FIND_STACK_BOUNDS) \
     || defined(MACOS_FIND_STACK_BOUNDS) || defined(ASSUME_FIXED_STACK_SIZE) \
     || defined(BEOS_FIND_STACK_BOUNDS) || defined(OSKIT_FIXED_STACK_BOUNDS) \
-    || defined(PALM_FIND_STACK_BOUNDS)
+    || defined(PALM_FIND_STACK_BOUNDS) || defined(PTHREAD_STACKSEG_FIND_STACK_BOUNDS)
 # define USE_STACK_BOUNDARY_VAR
 THREAD_LOCAL_DECL(extern uintptr_t scheme_stack_boundary);
 /* Same as scheme_stack_boundary, but set to an extreme value when feul auto-expires,