Fix dwarf3 compile_unit debug info

[Alexandre Oliva <aoliva at redhat dot com>]

When the PC range of a compile unit is not contiguous, we emit a
non-standard DW_AT_entry_pc as an attribute for a compile_unit node in
dwarf3 debug info, instead of the standard DW_AT_low_pc.

Also, we fail to emit DW_AT_ranges for such a node.

This patch fixes both points.

I tested it with both hot/cold splitting and function sections, as
well as with a full bootstrap&test cycle on amd64-linux-gnu.

The ranges probably won't quite work as expected in case of discarded
sections (.GNU.linkonce, garbage collected or merged), since IIRC
removed labels will resolve to zero in debug sections, and this will
make the range list appear to be terminated at that point.  I don't
see any way to avoid this, unfortunately.  Any ideas?

Note that the same information is available in DW_AT_low/high_pc or
DW_AT_ranges in individual functions, and most of the information
(except for hot/cold splitting IIRC) is available in .debug_aranges,
but aranges don't have the same problem because, unlike ranges, the
end address is given not by the explicit address, but by an offset, so
it won't be zero even if the section is discarded.  A zero base
address with a non-zero offset, however, could turn into a different
problem.  I haven't tackled any of the aranges issues in this patch.

Ok to install?

for gcc/ChangeLog
from  Alexandre Oliva  <aoliva@redhat.com>

	* dwarf2out.c (dw_ranges_by_label_ref): New typedef.
	(dw_ranges_struct): Rename block_num to num.  Adjust.
	(dw_ranges_by_label_struct): New.
	(ranges_by_label, ranges_by_label_allocated,
	ranges_by_label_in_use): New variables.
	(add_ranges_num): Factored most of the code out of...
	(add_ranges): ... this one.  Rewrite in terms of the former.
	(add_ranges_by_labels): New.
	(output_ranges): Output by-label ranges.
	(dwarf2out_finish): Output range for multiple-section
	compile_unit.  Output standard DW_AT_low_pc in addition to
	unexpected DW_AT_entry_pc.

Index: gcc/dwarf2out.c
===================================================================
--- gcc/dwarf2out.c.orig	2006-12-26 03:00:57.000000000 -0200
+++ gcc/dwarf2out.c	2006-12-26 03:01:02.000000000 -0200
@@ -3683,6 +3683,7 @@ typedef struct dw_line_info_struct *dw_l
 typedef struct dw_separate_line_info_struct *dw_separate_line_info_ref;
 typedef struct pubname_struct *pubname_ref;
 typedef struct dw_ranges_struct *dw_ranges_ref;
+typedef struct dw_ranges_by_label_struct *dw_ranges_by_label_ref;
 
 /* Each entry in the line_info_table maintains the file and
    line number associated with the label generated for that
@@ -3765,7 +3766,15 @@ DEF_VEC_ALLOC_O(pubname_entry, gc);
 
 struct dw_ranges_struct GTY(())
 {
-  int block_num;
+  /* If this is positive, it's a block number, otherwise it's a
+     bitwise-negated index into dw_ranges_by_label.  */
+  int num;
+};
+
+struct dw_ranges_by_label_struct GTY(())
+{
+  const char *begin;
+  const char *end;
 };
 
 /* The limbo die list structure.  */
@@ -3972,6 +3981,16 @@ static GTY(()) unsigned ranges_table_all
 /* Number of elements in ranges_table currently in use.  */
 static GTY(()) unsigned ranges_table_in_use;
 
+/* Array of pairs of labels referenced in ranges_table.  */
+static GTY ((length ("ranges_by_label_allocated")))
+     dw_ranges_by_label_ref ranges_by_label;
+
+/* Number of elements currently allocated for ranges_by_label.  */
+static GTY(()) unsigned ranges_by_label_allocated;
+
+/* Number of elements in ranges_by_label currently in use.  */
+static GTY(()) unsigned ranges_by_label_in_use;
+
 /* Size (in elements) of increments by which we may expand the
    ranges_table.  */
 #define RANGES_TABLE_INCREMENT 64
@@ -4128,7 +4147,9 @@ static void add_pubtype (tree, dw_die_re
 static void output_pubnames (VEC (pubname_entry,gc) *);
 static void add_arange (tree, dw_die_ref);
 static void output_aranges (void);
+static unsigned int add_ranges_num (int);
 static unsigned int add_ranges (tree);
+static unsigned int add_ranges_by_labels (const char *, const char *);
 static void output_ranges (void);
 static void output_line_info (void);
 static void output_file_names (void);
@@ -7531,7 +7552,7 @@ output_aranges (void)
    was placed.  */
 
 static unsigned int
-add_ranges (tree block)
+add_ranges_num (int num)
 {
   unsigned int in_use = ranges_table_in_use;
 
@@ -7545,12 +7566,48 @@ add_ranges (tree block)
 	      RANGES_TABLE_INCREMENT * sizeof (struct dw_ranges_struct));
     }
 
-  ranges_table[in_use].block_num = (block ? BLOCK_NUMBER (block) : 0);
+  ranges_table[in_use].num = num;
   ranges_table_in_use = in_use + 1;
 
   return in_use * 2 * DWARF2_ADDR_SIZE;
 }
 
+/* Add a new entry to .debug_ranges corresponding to a block, or a
+   range terminator if BLOCK is NULL.  */
+
+static unsigned int
+add_ranges (tree block)
+{
+  return add_ranges_num (block ? BLOCK_NUMBER (block) : 0);
+}
+
+/* Add a new entry to .debug_ranges corresponding to a pair of
+   labels.  */
+
+static unsigned int
+add_ranges_by_labels (const char *begin, const char *end)
+{
+  unsigned int in_use = ranges_by_label_in_use;
+
+  if (in_use == ranges_by_label_allocated)
+    {
+      ranges_by_label_allocated += RANGES_TABLE_INCREMENT;
+      ranges_by_label
+	= ggc_realloc (ranges_by_label,
+		       (ranges_by_label_allocated
+			* sizeof (struct dw_ranges_by_label_struct)));
+      memset (ranges_by_label + ranges_by_label_in_use, 0,
+	      RANGES_TABLE_INCREMENT
+	      * sizeof (struct dw_ranges_by_label_struct));
+    }
+
+  ranges_by_label[in_use].begin = begin;
+  ranges_by_label[in_use].end = end;
+  ranges_by_label_in_use = in_use + 1;
+
+  return add_ranges_num (-(int)in_use - 1);
+}
+
 static void
 output_ranges (void)
 {
@@ -7560,9 +7617,9 @@ output_ranges (void)
 
   for (i = 0; i < ranges_table_in_use; i++)
     {
-      int block_num = ranges_table[i].block_num;
+      int block_num = ranges_table[i].num;
 
-      if (block_num)
+      if (block_num > 0)
 	{
 	  char blabel[MAX_ARTIFICIAL_LABEL_BYTES];
 	  char elabel[MAX_ARTIFICIAL_LABEL_BYTES];
@@ -7582,10 +7639,10 @@ output_ranges (void)
 				    text_section_label, NULL);
 	    }
 
-	  /* Otherwise, we add a DW_AT_entry_pc attribute to force the
-	     compilation unit base address to zero, which allows us to
-	     use absolute addresses, and not worry about whether the
-	     target supports cross-section arithmetic.  */
+	  /* Otherwise, the compilation unit base address is zero,
+	     which allows us to use absolute addresses, and not worry
+	     about whether the target supports cross-section
+	     arithmetic.  */
 	  else
 	    {
 	      dw2_asm_output_addr (DWARF2_ADDR_SIZE, blabel,
@@ -7595,6 +7652,38 @@ output_ranges (void)
 
 	  fmt = NULL;
 	}
+
+      /* Negative block_num stands for an index into ranges_by_label.  */
+      else if (block_num < 0)
+	{
+	  int lab_idx = - block_num - 1;
+
+	  if (!have_multiple_function_sections)
+	    {
+	      gcc_unreachable ();
+#if 0
+	      /* If we ever use add_ranges_by_labels () for a single
+		 function section, all we have to do is to take out
+		 the #if 0 above.  */
+	      dw2_asm_output_delta (DWARF2_ADDR_SIZE,
+				    ranges_by_label[lab_idx].begin,
+				    text_section_label,
+				    fmt, i * 2 * DWARF2_ADDR_SIZE);
+	      dw2_asm_output_delta (DWARF2_ADDR_SIZE,
+				    ranges_by_label[lab_idx].end,
+				    text_section_label, NULL);
+#endif
+	    }
+	  else
+	    {
+	      dw2_asm_output_addr (DWARF2_ADDR_SIZE,
+				   ranges_by_label[lab_idx].begin,
+				   fmt, i * 2 * DWARF2_ADDR_SIZE);
+	      dw2_asm_output_addr (DWARF2_ADDR_SIZE,
+				   ranges_by_label[lab_idx].end,
+				   NULL);
+	    }
+	}
       else
 	{
 	  dw2_asm_output_data (DWARF2_ADDR_SIZE, 0, NULL);
@@ -14374,10 +14463,43 @@ dwarf2out_finish (const char *filename)
       add_AT_lbl_id (comp_unit_die, DW_AT_high_pc, text_end_label);
     }
 
-  /* If it wasn't, we need to give .debug_loc and .debug_ranges an appropriate
-     "base address".  Use zero so that these addresses become absolute.  */
-  else if (have_location_lists || ranges_table_in_use)
-    add_AT_addr (comp_unit_die, DW_AT_entry_pc, const0_rtx);
+  else
+    {
+      unsigned fde_idx = 0;
+
+      /* We need to give .debug_loc and .debug_ranges an appropriate
+	 "base address".  Use zero so that these addresses become
+	 absolute.  Historically, we've emitted the unexpected
+	 DW_AT_entry_pc instead of DW_AT_low_pc for this purpose.
+	 Emit both to give time for other tools to adapt.  */
+      add_AT_addr (comp_unit_die, DW_AT_low_pc, const0_rtx);
+      add_AT_addr (comp_unit_die, DW_AT_entry_pc, const0_rtx);
+
+      add_AT_range_list (comp_unit_die, DW_AT_ranges,
+			 add_ranges_by_labels (text_section_label,
+					       text_end_label));
+      if (flag_reorder_blocks_and_partition)
+	add_ranges_by_labels (cold_text_section_label,
+			      cold_end_label);
+
+      for (fde_idx = 0; fde_idx < fde_table_in_use; fde_idx++)
+	{
+	  dw_fde_ref fde = &fde_table[fde_idx];
+
+	  if (fde->dw_fde_switched_sections)
+	    {
+	      add_ranges_by_labels (fde->dw_fde_hot_section_label,
+				    fde->dw_fde_hot_section_end_label);
+	      add_ranges_by_labels (fde->dw_fde_unlikely_section_label,
+				    fde->dw_fde_unlikely_section_end_label);
+	    }
+	  else
+	    add_ranges_by_labels (fde->dw_fde_begin,
+				  fde->dw_fde_end);
+	}
+
+      add_ranges (NULL);
+    }
 
   /* Output location list section if necessary.  */
   if (have_location_lists)

-- 
Alexandre Oliva         http://www.lsd.ic.unicamp.br/~oliva/
FSF Latin America Board Member         http://www.fsfla.org/
Red Hat Compiler Engineer   aoliva@{redhat.com, gcc.gnu.org}
Free Software Evangelist  oliva@{lsd.ic.unicamp.br, gnu.org}