[RFA] Patch to skip_prologue_using_sal() for oneline stub functions

[Fred Fish]

If a function optimizes down to a single return instruction, there is
no prologue, and skip_prologue_using_sal will return a PC that is
probably the first instruction of the next following function.  In
this case, we want to return the start_pc, so that the caller will
know that it needs to run the architecture specific prologue scanner
to figure out what is going on.

This fixes the following failures for MIPS:

  FAIL: gdb.base/break.exp: breakpoint small function, optimized file
  FAIL: gdb.base/break.exp: run until function breakpoint, optimized file
  FAIL: gdb.base/break.exp: run until breakpoint set at small function, optimized file

-Fred

============================================================================

2006-05-10  Fred Fish  <fnf@specifix.com>

	* symtab.c (skip_prologue_using_sal): Handle single line functions
	like "foo(){}", which may optimize down to a single return inst.

Index: symtab.c
===================================================================
RCS file: /cvs/src/src/gdb/symtab.c,v
retrieving revision 1.146
diff -c -p -r1.146 symtab.c
*** symtab.c	17 Dec 2005 22:34:03 -0000	1.146
--- symtab.c	10 May 2006 14:19:07 -0000
*************** skip_prologue_using_sal (CORE_ADDR func_
*** 4030,4035 ****
--- 4030,4040 ----
    prologue_sal = find_pc_line (start_pc, 0);
    if (prologue_sal.line != 0)
      {
+       /* If there is only one sal that covers the entire function,
+ 	 then it is probably a single line function, like
+ 	 "foo(){}". */
+       if (prologue_sal.end == end_pc)
+ 	return start_pc;
        while (prologue_sal.end < end_pc)
  	{
  	  struct symtab_and_line sal;