native gdb.sum gdb.base/interrupt.exp

[Richard Henderson]

On Fri, Aug 03, 2001 at 07:56:55PM +0200, Jan Hubicka wrote:
> > What if we attack the unaligned stack problem in main
> > by making main appear use alloca to align the frame?
> This sounds like good idea, modulo the pesimization of
> code in main. I am not sure how important it is except
> for trivial benchmarks.

I'm currently testing the following patch.  I've reverted the
ix86_output_main_function_alignment_hack patch in advance in
hopes of getting a clean run out of the regression tester.

At -O0, we get 

        andl    $-16, %esp
        movl    $0, %eax
        subl    %eax, %esp

which is slightly silly, but not overmuch.  With any optimization
things clean up as you'd hope.


r~


	* config/i386/i386.h (FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN): New.
	* function.c (expand_main_function): Implement it.
	* doc/tm.texi: Document it.

Index: function.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/function.c,v
retrieving revision 1.288
diff -u -p -r1.288 function.c
--- function.c	2001/08/01 18:03:28	1.288
+++ function.c	2001/08/04 16:49:09
@@ -6315,10 +6315,35 @@ mark_varargs ()
 void
 expand_main_function ()
 {
-#if !defined (HAS_INIT_SECTION)
+#ifdef FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN
+  if (FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN)
+    {
+      int align = PREFERRED_STACK_BOUNDARY / BITS_PER_UNIT;
+      rtx tmp;
+
+      /* Forcably align the stack.  */
+#ifdef STACK_GROWS_DOWNWARD
+      tmp = expand_binop (Pmode, and_optab, stack_pointer_rtx,
+			  GEN_INT (-align), stack_pointer_rtx, 1, OPTAB_WIDEN);
+#else
+      tmp = expand_binop (Pmode, add_optab, stack_pointer_rtx,
+			  GEN_INT (align - 1), NULL_RTX, 1, OPTAB_WIDEN);
+      tmp = expand_binop (Pmode, and_optab, tmp, GEN_INT (-align),
+			  stack_pointer_rtx, 1, OPTAB_WIDEN);
+#endif
+      if (tmp != stack_pointer_rtx)
+	emit_move_insn (stack_pointer_rtx, tmp);
+      
+      /* Enlist allocate_dynamic_stack_space to pick up the pieces.  */
+      tmp = force_reg (Pmode, const0_rtx);
+      allocate_dynamic_stack_space (tmp, NULL_RTX, BIGGEST_ALIGNMENT);
+    }
+#endif
+
+#ifndef HAS_INIT_SECTION
   emit_library_call (gen_rtx_SYMBOL_REF (Pmode, NAME__MAIN), 0,
 		     VOIDmode, 0);
-#endif /* not HAS_INIT_SECTION */
+#endif
 }
 
 extern struct obstack permanent_obstack;
Index: config/i386/i386.h
===================================================================
RCS file: /cvs/gcc/gcc/gcc/config/i386/i386.h,v
retrieving revision 1.195
diff -u -p -r1.195 i386.h
--- i386.h	2001/07/15 16:59:06	1.195
+++ i386.h	2001/08/04 16:49:11
@@ -640,6 +640,13 @@ extern int ix86_arch;
    aligned; the compiler cannot rely on having this alignment.  */
 #define PREFERRED_STACK_BOUNDARY ix86_preferred_stack_boundary
 
+/* As of July 2001, many runtimes to not align the stack properly when
+   entering main.  This causes expand_main_function to forcably align
+   the stack, which results in aligned frames for functions called from
+   main, though it does nothing for the alignment of main itself.  */
+#define FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN \
+  (ix86_preferred_stack_boundary > STACK_BOUNDARY)
+
 /* Allocation boundary for the code of a function. */
 #define FUNCTION_BOUNDARY 16
 
Index: doc/tm.texi
===================================================================
RCS file: /cvs/gcc/gcc/gcc/doc/tm.texi,v
retrieving revision 1.42
diff -u -p -r1.42 tm.texi
--- tm.texi	2001/08/04 01:31:41	1.42
+++ tm.texi	2001/08/04 16:49:15
@@ -1028,6 +1028,12 @@ for the desired alignment (measured in b
 also defined, this macro must evaluate to a value equal to or larger
 than @code{STACK_BOUNDARY}.
 
+@findex FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN
+@item FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN
+A C expression that evaluates true if @code{PREFERRED_STACK_BOUNDARY} is
+not guaranteed by the runtime and we should emit code to align the stack
+at the beginning of @code{main}.
+
 @cindex @code{PUSH_ROUNDING}, interaction with @code{PREFERRED_STACK_BOUNDARY}
 If @code{PUSH_ROUNDING} is not defined, the stack will always be aligned
 to the specified boundary.  If @code{PUSH_ROUNDING} is defined and specifies