Re: [RFA] Fix "break foo" when `foo's prologue ends before line table

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 11 May 2009 23:49:10 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: gdb-patches@sourceware.org
> 
> > Date: Mon, 11 May 2009 21:27:09 +0200
> > From: Joel Brobecker <brobecker@adacore.com>
> > Cc: gdb-patches@sourceware.org
> > 
> > I'm always reluctant to introduce code I don't understand, and usually
> > leave it out until I see a bug - that's why I was asking. Have you
> > tried without this part?
> 
> No, but I will.

OK, I tried it, and it does work, at least in the 2 test cases I could
try.

Here's an updated patch, which incorporates the comments in this
thread:

  . It uses a single symtab for the function's symbol
  . It stops looking as soon as it finds the first linetable entry
    whose PC is in the range of the function's PC values

OK to commit?

2009-05-09  Eli Zaretskii  <eliz@gnu.org>

	* symtab.c (skip_prologue_using_lineinfo): New function.
	(find_function_start_sal): Use it to get to the first line of
	function's body that has an entry in the lineinfo table.

--- symtab.c~0	2009-04-01 02:21:07.000000000 +0300
+++ symtab.c	2009-05-16 13:49:42.296906500 +0300
@@ -2599,6 +2599,46 @@
   return pc;
 }
 
+/* Given a function start address FUNC_ADDR and SYMTAB, find the first
+   address for that function that has an entry in SYMTAB's line info
+   table.  If such an entry cannot be found, return FUNC_ADDR
+   unaltered.  */
+CORE_ADDR
+skip_prologue_using_lineinfo (CORE_ADDR func_addr, struct symtab *symtab)
+{
+  CORE_ADDR func_start, func_end;
+  struct linetable *l;
+  int ind, i, len;
+  int best_lineno = 0;
+  CORE_ADDR best_pc = func_addr;
+
+  /* Get the range for the function's PC values, or give up if we
+     cannot, for some reason.  */
+  if (!find_pc_partial_function (func_addr, NULL, &func_start, &func_end))
+    return func_addr;
+
+  l = LINETABLE (symtab);
+  if (l == NULL)
+    return func_addr;
+
+  /* Linetable entries are ordered by PC values, see the commentary in
+     symtab.h where `struct linetable' is defined.  Thus, the first
+     entry whose PC is in the range [FUNC_START..FUNC_END] is the
+     address we are looking for.  */
+  for (i = 0; i < l->nitems; i++)
+    {
+      struct linetable_entry *item = &(l->item[i]);
+
+      /* Don't use line numbers of zero, they mark special entries in
+	 the table.  See the commentary on symtab.h before the
+	 definition of struct linetable.  */
+      if (item->line > 0 && func_start <= item->pc && item->pc <= func_end)
+	return item->pc;
+    }
+
+  return func_addr;
+}
+
 /* Given a function symbol SYM, find the symtab and line for the start
    of the function.
    If the argument FUNFIRSTLINE is nonzero, we want the first line
@@ -2649,6 +2689,15 @@
       sal = find_pc_sect_line (pc, SYMBOL_OBJ_SECTION (sym), 0);
     }
 
+  /* If we still don't have a valid source line, try to find the first
+     PC in the lineinfo table that belongs to the same function.  */
+  if (funfirstline && sal.symtab == NULL)
+    {
+      pc = skip_prologue_using_lineinfo (pc, SYMBOL_SYMTAB (sym));
+      /* Recalculate the line number.  */
+      sal = find_pc_sect_line (pc, SYMBOL_OBJ_SECTION (sym), 0);
+    }
+
   sal.pc = pc;
 
   return sal;