[RFA] Add option to skip prologue in "break FILE:LINENO" (take 2)

[Joel Brobecker <brobecker@adacore.com>]

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Hello,

Following a request for comments regarding a proposed change of behavior
when inserting a breakpoint on a specific line number, we received a
variety of comments, and it appears very clearly that the proposal
was at the very least controversial.

So, here is a new proposal where the existing behavior is preserved.
A new set/show command is introduced to allow the user to configure
GDB to activate the new proposed behavior:

    (gdb) set/show breakpoint skip-prologue

The help text for this command explains the purpose of this option:

  Set the debugger behavior when inserting a breakpoint on a specific line.
  When inserting a breakpoint on a specific line number that corresponds
  to the prologue of a function, the debugger will automatically adjust
  its location to the first line past the prologue if this option is set.

By default, this option is OFF, preserving the current behavior.
I think this should take care of all the objections I read so far.

2008-01-10  Joel Brobecker  <brobecker@adacore.com>

        * breakpoint.c (breakpoint_skip_prologue_p): New static global.
        (show_breakpoint_skip_prologue): New function.
        (skip_prologue_sal): New function.
        (resolve_sal_pc): Adjust SAL past prologue if the SAL was computed
        from a line number and breakpoint_skip_prologue_p is set.
        (_initialize_breakpoint): Add new set/show break skip-prologue
        command.

Tested on x86-linux, no regression.
A new testcase, a NEWs entry, and proper documentation will be submitted
later if the patch is approved.

OK to commit?

Thanks,
-- 
Joel

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Index: breakpoint.c
===================================================================
--- breakpoint.c	(revision 117)
+++ breakpoint.c	(revision 124)
@@ -246,6 +246,20 @@ Automatic usage of hardware breakpoints 
 		    value);
 }
 
+/* When a user inserts a breakpoint on a specific line that corresponds
+   to a function prologue, GDB should automatically adjust the location
+   to the first line past the prologue if BREAKPOINT_SKIP_PROLOGUE_P
+   is non-zero.  */
+static int breakpoint_skip_prologue_p = 0;
+static void
+show_breakpoint_skip_prologue (struct ui_file *file, int from_tty,
+			       struct cmd_list_element *c, const char *value)
+{
+  fprintf_filtered (file, _("\
+When breaking on a specific line, automatic adjustment of the breakpoint\n\
+location past the function prologue is %s.\n"),
+		    value);
+}
 
 void _initialize_breakpoint (void);
 
@@ -5446,6 +5460,25 @@ gdb_breakpoint (char *address, char *con
 			       0);
 }
 
+/* Adjust SAL to the first instruction past the function prologue.
+   The end of the prologue is determined using the line table from
+   the debugging information.
+
+   If SAL is already past the prologue, then do nothing.  */
+
+static void
+skip_prologue_sal (struct symtab_and_line *sal)
+{
+  struct symbol *sym = find_pc_function (sal->pc);
+  struct symtab_and_line start_sal;
+
+  if (sym == NULL)
+    return;
+
+  start_sal = find_function_start_sal (sym, 1);
+  if (sal->pc < start_sal.pc)
+    *sal = start_sal;
+}
 
 /* Helper function for break_command_1 and disassemble_command.  */
 
@@ -5460,6 +5493,13 @@ resolve_sal_pc (struct symtab_and_line *
 	error (_("No line %d in file \"%s\"."),
 	       sal->line, sal->symtab->filename);
       sal->pc = pc;
+
+      /* If this SAL corresponds to a breakpoint inserted using
+         a line number, and the debugger is configured to skip
+         function prologues in that case, then adjust the SAL
+         if necessary.  */
+      if (sal->explicit_line && breakpoint_skip_prologue_p)
+        skip_prologue_sal (sal);
     }
 
   if (sal->section == 0 && sal->symtab != NULL)
@@ -8282,6 +8322,18 @@ a warning will be emitted for such break
 			   show_automatic_hardware_breakpoints,
 			   &breakpoint_set_cmdlist,
 			   &breakpoint_show_cmdlist);
-  
+
+  add_setshow_boolean_cmd ("skip-prologue", class_breakpoint,
+                           &breakpoint_skip_prologue_p, _("\
+Set the debugger behavior when inserting a breakpoint on a specific line."),
+                           _("\
+Show the debugger behavior when inserting a breakpoint on a specific line."),
+                           _("\
+When inserting a breakpoint on a specific line number that corresponds\n\
+to the prologue of a function, the debugger will automatically adjust\n\
+its location to the first line past the prologue if this option is set."),
+                           NULL, show_breakpoint_skip_prologue,
+                           &breakpoint_set_cmdlist, &breakpoint_show_cmdlist);
+
   automatic_hardware_breakpoints = 1;
 }