Re: RFA: Fix calculation of size of builtin setjmp buffer

[Nicholas Clifton <nickc at redhat dot com>]

Hi Jakub,

> But what will this do on targets where POINTER_SIZE is smaller than
> BITS_PER_WORD?  E.g. I think some options on s390 or ppc.
> If you want it to be always 5 pointers, then you want
>    tmp = size_int (4);
> and not something else, otherwise it really depends on how exactly it is
> used, perhaps it can be 5 * MAX (BITS_PER_WORD / POINTER_SIZE, 1) - 1
> or whatever else, but 5 * POINTER_SIZE / BITS_PER_WORD is definitely wrong.

Ah -I had not considered this.

OK - how about this revision ?  It allocates a buffer big enough to hold 
5 things, either pointers or words, whichever is bigger.  The comments 
are suitably adjusted as well.

Cheers
  Nick


Index: gcc/except.c
===================================================================
--- gcc/except.c	(revision 210096)
+++ gcc/except.c	(working copy)
@@ -286,8 +286,9 @@
       tmp = size_int (FIRST_PSEUDO_REGISTER + 2 - 1);
 #endif
 #else
-      /* builtin_setjmp takes a pointer to 5 words.  */
-      tmp = size_int (5 * BITS_PER_WORD / POINTER_SIZE - 1);
+      /* builtin_setjmp uses a buffer big enough to hold
+	 5 pointers or 5 words, whichever is bigger.  */
+      tmp = size_int ((5 * MAX (POINTER_SIZE, BITS_PER_WORD)) / 
BITS_PER_WORD - 1);
 #endif
       tmp = build_index_type (tmp);
       tmp = build_array_type (ptr_type_node, tmp);
Index: gcc/builtins.c
===================================================================
--- gcc/builtins.c	(revision 210096)
+++ gcc/builtins.c	(working copy)
@@ -977,10 +977,10 @@
   emit_insn (gen_blockage ());
 }

-/* __builtin_longjmp is passed a pointer to an array of five words (not
-   all will be used on all machines).  It operates similarly to the C
-   library function of the same name, but is more efficient.  Much of
-   the code below is copied from the handling of non-local gotos.  */
+/* __builtin_longjmp is passed a pointer to an array of five word/pointer
+   sized entries, not all will be used on all machines.  It operates 
similarly
+   to the C library function of the same name, but is more efficient.  Much
+   of the code below is copied from the handling of non-local gotos.  */

 static void
 expand_builtin_longjmp (rtx buf_addr, rtx value)
@@ -1204,10 +1204,10 @@
   return const0_rtx;
 }

-/* __builtin_update_setjmp_buf is passed a pointer to an array of five 
words
-   (not all will be used on all machines) that was passed to 
__builtin_setjmp.
-   It updates the stack pointer in that block to correspond to the current
-   stack pointer.  */
+/* __builtin_update_setjmp_buf is passed a pointer to an array of five
+   entries (not all will be used on all machines) that was passed to
+   __builtin_setjmp.  It updates the stack pointer in that block to
+   correspond to the current stack pointer.  */

 static void
 expand_builtin_update_setjmp_buf (rtx buf_addr)
@@ -6205,8 +6205,8 @@
       gcc_unreachable ();

     case BUILT_IN_SETJMP_SETUP:
-      /* __builtin_setjmp_setup is passed a pointer to an array of five 
words
-          and the receiver label.  */
+      /* __builtin_setjmp_setup is passed a pointer to an array of five
+	 entries and the receiver label.  */
       if (validate_arglist (exp, POINTER_TYPE, POINTER_TYPE, VOID_TYPE))
 	{
 	  rtx buf_addr = expand_expr (CALL_EXPR_ARG (exp, 0), subtarget,
@@ -6239,9 +6239,9 @@
 	}
       break;

-      /* __builtin_longjmp is passed a pointer to an array of five words.
-	 It's similar to the C library longjmp function but works with
-	 __builtin_setjmp above.  */
+      /* __builtin_longjmp is passed a pointer to an array of five
+	 entries.  It's similar to the C library longjmp function
+	 but works with __builtin_setjmp above.  */
     case BUILT_IN_LONGJMP:
       if (validate_arglist (exp, POINTER_TYPE, INTEGER_TYPE, VOID_TYPE))
 	{
Index: gcc/doc/md.texi
===================================================================
--- gcc/doc/md.texi	(revision 210096)
+++ gcc/doc/md.texi	(working copy)
@@ -6112,10 +6112,15 @@
 A typical reason why you might need this pattern is if some value, such
 as a pointer to a global table, must be restored.  Though it is
 preferred that the pointer value be recalculated if possible (given the
-address of a label for instance).  The single argument is a pointer to
-the @code{jmp_buf}.  Note that the buffer is five words long and that
-the first three are normally used by the generic mechanism.
+address of a label for instance).

+The single argument is a pointer to the @code{jmp_buf}.  This buffer
+is big enough to hold five @code{word_mode} or @code{Pmode} sized
+entries, whichever is bigger.  The generic machanism uses just the
+first three entries, (to hold the frame pointer, return address and
+stack pointer respectively), but target specific code can use all five
+of them.
+
 @cindex @code{builtin_setjmp_receiver} instruction pattern
 @item @samp{builtin_setjmp_receiver}
 This pattern, if defined, contains code needed at the site of a