Add support for detecting register-stack overrun on IA64.

Per recent investigation, the register stack can grow faster than the
regular stack depending on compiler and choice of options.  To avoid
crashes we must check both stacks in check_stack_depth().

Since this is poorly-tested code, committing only to HEAD for the
moment ... but we might want to consider back-patching later.

src/backend/tcop/postgres.c

@@ -119,6 +119,12 @@ static long max_stack_depth_bytes = 100 * 1024L;
  */
 char	   *stack_base_ptr = NULL;
 
+/*
+ * On IA64 we also have to remember the register stack base.
+ */
+#if defined(__ia64__) || defined(__ia64)
+char	   *register_stack_base_ptr = NULL;
+#endif
 
 /*
  * Flag to mark SIGHUP. Whenever the main loop comes around it
@@ -2983,6 +2989,35 @@ ProcessInterrupts(void)
 }
 
 
+/*
+ * IA64-specific code to fetch the AR.BSP register for stack depth checks.
+ *
+ * We currently support gcc and icc here.
+ */
+#if defined(__ia64__) || defined(__ia64)
+
+#include <asm/ia64regs.h>
+
+static __inline__ char *
+ia64_get_bsp(void)
+{
+	char	   *ret;
+
+#ifndef __INTEL_COMPILER
+	/* the ;; is a "stop", seems to be required before fetching BSP */
+	__asm__ __volatile__(
+		";;\n"
+		"	mov	%0=ar.bsp	\n"
+:		"=r"(ret));
+#else
+  ret = (char *) __getReg(_IA64_REG_AR_BSP);
+#endif
+  return ret;
+}
+
+#endif /* IA64 */
+
+
 /*
  * check_stack_depth: check for excessively deep recursion
  *
@@ -3026,6 +3061,29 @@ check_stack_depth(void)
 						 "after ensuring the platform's stack depth limit is adequate.",
 						 max_stack_depth)));
 	}
+
+	/*
+	 * On IA64 there is a separate "register" stack that requires its own
+	 * independent check.  For this, we have to measure the change in the
+	 * "BSP" pointer from PostgresMain to here.  Logic is just as above,
+	 * except that we know IA64's register stack grows up.
+	 *
+	 * Note we assume that the same max_stack_depth applies to both stacks.
+	 */
+#if defined(__ia64__) || defined(__ia64)
+	stack_depth = (long) (ia64_get_bsp() - register_stack_base_ptr);
+
+	if (stack_depth > max_stack_depth_bytes &&
+		register_stack_base_ptr != NULL)
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_STATEMENT_TOO_COMPLEX),
+				 errmsg("stack depth limit exceeded"),
+				 errhint("Increase the configuration parameter \"max_stack_depth\" (currently %dkB), "
+						 "after ensuring the platform's stack depth limit is adequate.",
+						 max_stack_depth)));
+	}
+#endif /* IA64 */
 }
 
 /* GUC assign hook for max_stack_depth */
@@ -3435,6 +3493,9 @@ PostgresMain(int argc, char *argv[], const char *username)
 
 	/* Set up reference point for stack depth checking */
 	stack_base_ptr = &stack_base;
+#if defined(__ia64__) || defined(__ia64)
+	register_stack_base_ptr = ia64_get_bsp();
+#endif
 
 	/* Compute paths, if we didn't inherit them from postmaster */
 	if (my_exec_path[0] == '\0')