[PATCH] add -fprolog-pad=N option to c-family

[Torsten Duwe <duwe at suse dot de>]

Hi Maxim,

thanks for starting the work on this; I have added the missing
command line option. It builds now and the resulting compiler generates
a linux kernel with the desired properties, so work can continue there.

	Torsten

diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 9bc02fc..57265c5 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -393,6 +393,7 @@ static tree handle_designated_init_attribute (tree *, tree, tree, int, bool *);
 static tree handle_bnd_variable_size_attribute (tree *, tree, tree, int, bool *);
 static tree handle_bnd_legacy (tree *, tree, tree, int, bool *);
 static tree handle_bnd_instrument (tree *, tree, tree, int, bool *);
+static tree handle_prolog_pad_attribute (tree *, tree, tree, int, bool *);
 
 static void check_function_nonnull (tree, int, tree *);
 static void check_nonnull_arg (void *, tree, unsigned HOST_WIDE_INT);
@@ -833,6 +834,8 @@ const struct attribute_spec c_common_attribute_table[] =
 			      handle_bnd_legacy, false },
   { "bnd_instrument",         0, 0, true, false, false,
 			      handle_bnd_instrument, false },
+  { "prolog_pad",	      1, 1, false, true, true,
+			      handle_prolog_pad_attribute, false },
   { NULL,                     0, 0, false, false, false, NULL, false }
 };
 
@@ -9663,6 +9666,16 @@ handle_designated_init_attribute (tree *node, tree name, tree, int,
   return NULL_TREE;
 }
 
+static tree
+handle_prolog_pad_attribute (tree *, tree name, tree, int,
+			     bool *)
+{
+  warning (OPT_Wattributes,
+	   "%qE attribute is used", name);
+
+  return NULL_TREE;
+}
+
 
 /* Check for valid arguments being passed to a function with FNTYPE.
    There are NARGS arguments in the array ARGARRAY.  */
diff --git a/gcc/c-family/c-opts.c b/gcc/c-family/c-opts.c
index 9ae181f..31a8026 100644
--- a/gcc/c-family/c-opts.c
+++ b/gcc/c-family/c-opts.c
@@ -532,6 +532,10 @@ c_common_handle_option (size_t scode, const char *arg, int value,
       cpp_opts->ext_numeric_literals = value;
       break;
 
+    case OPT_fprolog_pad_:
+      prolog_nop_pad_size = value;
+      break;
+
     case OPT_idirafter:
       add_path (xstrdup (arg), AFTER, 0, true);
       break;
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index aafd802..929ebb6 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -1407,6 +1407,10 @@ fpreprocessed
 C ObjC C++ ObjC++
 Treat the input file as already preprocessed.
 
+fprolog-pad=
+C ObjC C++ ObjC++ RejectNegative Joined UInteger Var(prolog_nop_pad_size) Init(0)
+Pad NOPs before each function prolog
+
 ftrack-macro-expansion
 C ObjC C++ ObjC++ JoinedOrMissing RejectNegative UInteger
 ; converted into ftrack-macro-expansion=
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 1ce7181..9d10b10 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -4553,6 +4553,10 @@ will select the smallest suitable mode.
 This section describes the macros that output function entry
 (@dfn{prologue}) and exit (@dfn{epilogue}) code.
 
+@deftypefn {Target Hook} void TARGET_ASM_PRINT_PROLOG_PAD (FILE *@var{file}, unsigned HOST_WIDE_INT @var{pad_size}, bool @var{record_p})
+Generate prologue pad
+@end deftypefn
+
 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_PROLOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size})
 If defined, a function that outputs the assembler code for entry to a
 function.  The prologue is responsible for setting up the stack frame,
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index a0a0a81..bda6d5c 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -3662,6 +3662,8 @@ will select the smallest suitable mode.
 This section describes the macros that output function entry
 (@dfn{prologue}) and exit (@dfn{epilogue}) code.
 
+@hook TARGET_ASM_PRINT_PROLOG_PAD
+
 @hook TARGET_ASM_FUNCTION_PROLOGUE
 
 @hook TARGET_ASM_FUNCTION_END_PROLOGUE
diff --git a/gcc/final.c b/gcc/final.c
index 1edc446..e0cff80 100644
--- a/gcc/final.c
+++ b/gcc/final.c
@@ -1753,6 +1753,7 @@ void
 final_start_function (rtx_insn *first, FILE *file,
 		      int optimize_p ATTRIBUTE_UNUSED)
 {
+  unsigned HOST_WIDE_INT pad_size = prolog_nop_pad_size;
   block_depth = 0;
 
   this_is_asm_operands = 0;
@@ -1765,6 +1766,21 @@ final_start_function (rtx_insn *first, FILE *file,
 
   high_block_linenum = high_function_linenum = last_linenum;
 
+  tree prolog_pad_attr
+    = lookup_attribute ("prolog_pad", TYPE_ATTRIBUTES (TREE_TYPE (current_function_decl)));
+  if (prolog_pad_attr)
+    {
+      tree prolog_pad_value = TREE_VALUE (TREE_VALUE (prolog_pad_attr));
+
+      if (tree_fits_uhwi_p (prolog_pad_value))
+	pad_size = tree_to_uhwi (prolog_pad_value);
+      else
+	gcc_unreachable ();
+
+    }
+  if (pad_size > 0)
+    targetm.asm_out.print_prolog_pad (file, pad_size, true);
+
   if (flag_sanitize & SANITIZE_ADDRESS)
     asan_function_start ();
 
diff --git a/gcc/target.def b/gcc/target.def
index d754337..63d3285 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -288,6 +288,12 @@ hidden, protected or internal visibility as specified by @var{visibility}.",
  void, (tree decl, int visibility),
  default_assemble_visibility)
 
+DEFHOOK
+(print_prolog_pad,
+ "Generate prologue pad",
+ void, (FILE *file, unsigned HOST_WIDE_INT pad_size, bool record_p),
+ default_print_prolog_pad)
+
 /* Output the assembler code for entry to a function.  */
 DEFHOOK
 (function_prologue,
diff --git a/gcc/targhooks.c b/gcc/targhooks.c
index dcf0863..05ab26d 100644
--- a/gcc/targhooks.c
+++ b/gcc/targhooks.c
@@ -1499,6 +1499,23 @@ default_use_by_pieces_infrastructure_p (unsigned HOST_WIDE_INT size,
   return move_by_pieces_ninsns (size, alignment, max_size + 1) < ratio;
 }
 
+void
+default_print_prolog_pad (FILE *file, unsigned HOST_WIDE_INT pad_size,
+			  bool record_p)
+{
+  if (record_p)
+    fprintf (file, "1:");
+  for (unsigned i = 0; i < pad_size; ++i)
+    fprintf (file, "\tnop\n");
+  if (record_p)
+    {
+      fprintf (file, "\t.section __prolog_pads_loc, \"a\",@progbits\n");
+      fprintf (file, "\t.quad 1b\n");
+      fprintf (file, "\t.long %lu\n", pad_size);
+      fprintf (file, "\t.previous\n");
+    }
+}
+
 bool
 default_profile_before_prologue (void)
 {
diff --git a/gcc/targhooks.h b/gcc/targhooks.h
index 47b5cfc..d03f993 100644
--- a/gcc/targhooks.h
+++ b/gcc/targhooks.h
@@ -199,6 +199,7 @@ extern bool default_use_by_pieces_infrastructure_p (unsigned HOST_WIDE_INT,
 						    enum by_pieces_operation,
 						    bool);
 
+extern void default_print_prolog_pad (FILE *, unsigned HOST_WIDE_INT , bool);
 extern bool default_profile_before_prologue (void);
 extern reg_class_t default_preferred_reload_class (rtx, reg_class_t);
 extern reg_class_t default_preferred_output_reload_class (rtx, reg_class_t);
diff --git a/gcc/testsuite/c-c++-common/attribute-prolog_pad-1.c b/gcc/testsuite/c-c++-common/attribute-prolog_pad-1.c
new file mode 100644
index 0000000..7404dc5
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attribute-prolog_pad-1.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+
+void f1(void) __attribute__((prolog_pad(1)));
+void f2(void) __attribute__((prolog_pad(2)));
+
+void
+f1 (void)
+{
+  f2 ();
+}
+
+void f2 (void)
+{
+  f1 ();
+}