Re: i386 stack missalignment on main

[Jan Hubicka <jh at suse dot cz>]

> On Mon, Jul 30, 2001 at 02:16:52PM +0200, Jan Hubicka wrote:
> > I need to augument gcc to output something like
> > 
> > .globl main:
> > main:
> > <align stack and move arguments>
> > call label
> > <return>
> > label:
> > normal code
> > 
> > and whether it is safe to expect main to have maximally two arguments then.
> 
> No, you can't.  First, main has 3 arguments.  Two, you've
> got to return the stack to normal when leaving main, so
> no simple hack is going to cut it.
Here is updated patch.  It accepts main with 3 arguments.
The returning is handled properly too.

Mon Jul 30 15:25:00 CEST 2001  Jan Hubicka  <jh@suse.cz>

	* i386.c (ix86_output_main_function_alignment_hack): New function.
	(TARGET_ASM_FUNCTION_PROLOGUE): Default to it.

Index: i386.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/config/i386/i386.c,v
retrieving revision 1.289
diff -c -3 -p -r1.289 i386.c
*** i386.c	2001/07/23 21:16:01	1.289
--- i386.c	2001/07/30 16:59:59
*************** static HOST_WIDE_INT ix86_GOT_alias_set 
*** 574,579 ****
--- 574,580 ----
  static void ix86_adjust_counter PARAMS ((rtx, HOST_WIDE_INT));
  static rtx ix86_expand_aligntest PARAMS ((rtx, int));
  static void ix86_expand_strlensi_unroll_1 PARAMS ((rtx, rtx));
+ static void ix86_output_main_function_alignment_hack PARAMS ((FILE *f, int));
  
  struct ix86_address
  {
*************** static int ix86_comp_type_attributes PAR
*** 634,639 ****
--- 635,644 ----
  							  HOST_WIDE_INT));
  #  undef TARGET_ASM_FUNCTION_PROLOGUE
  #  define TARGET_ASM_FUNCTION_PROLOGUE ix86_osf_output_function_prologue
+ #else
+ #  undef TARGET_ASM_FUNCTION_PROLOGUE
+ #  define TARGET_ASM_FUNCTION_PROLOGUE \
+    ix86_output_main_function_alignment_hack
  #endif
  
  #undef TARGET_ASM_OPEN_PAREN
*************** ix86_memory_move_cost (mode, class, in)
*** 10774,10777 ****
--- 10779,10824 ----
  	return ((in ? ix86_cost->int_load[2] : ix86_cost->int_store[2])
  		* (int) GET_MODE_SIZE (mode) / 4);
      }
+ }
+ 
+ /* Most of current runtimes (Jul 2001) do not align stack properly when
+    entering main, so emit an wrapper to align stack before the real main
+    code is called.
+   
+    This can eventually go if we manage to fix the runtimes or teach gcc
+    to dynamically align stack in main automatically.
+ 
+    Adding check to configure is probably not good idea, as binarry can move
+    from one shared library to older.  */
+ 
+ static void
+ ix86_output_main_function_alignment_hack (file, size)
+      FILE *file;
+      int size ATTRIBUTE_UNUSED;
+ {
+   rtx label;
+   char buf[256];
+   /* Check that we see main function with maximally 8 bytes of arguments.
+      if so, emit the hack to align stack for runtimes, where this constraint
+      is broken.  */
+   if (strcmp (cfun->name, "main"))
+     return;
+   if (cfun->pops_args || cfun->args_size > 12)
+     return;
+   if (PREFERRED_STACK_BOUNDARY <= 2)
+     return;
+   label = gen_label_rtx ();
+   fprintf (file, "\tpushl\t%%ebp\n");
+   fprintf (file, "\tmovl\t%%esp, %%ebp\n");
+   fprintf (file, "\tandl\t$0xfffffff0, %%esp\n");
+   fprintf (file, "\tpushl\t%%ebp\n");
+   fprintf (file, "\tpushl\t16(%%ebp)\n");
+   fprintf (file, "\tpushl\t12(%%ebp)\n");
+   fprintf (file, "\tpushl\t8(%%ebp)\n");
+   fprintf (file, "\tcall\t");
+   ASM_GENERATE_INTERNAL_LABEL (buf, "L", CODE_LABEL_NUMBER (label));
+   assemble_name (file, buf);
+   fprintf (file, "\n\tleave\n");
+   fprintf (file, "\tret\n");
+   ASM_OUTPUT_INTERNAL_LABEL (file, "L", CODE_LABEL_NUMBER (label));
  }