tui/1963: segfault when navigating in 'layout asm'

Joshua Neuheisel jneuheisel@gmail.com
Wed Nov 23 13:28:00 GMT 2005


The following reply was made to PR tui/1963; it has been noted by GNATS.

From: Joshua Neuheisel <jneuheisel@gmail.com>
To: gdb-gnats@sources.redhat.com
Cc:  
Subject: Re: tui/1963: segfault when navigating in 'layout asm'
Date: Wed, 23 Nov 2005 08:23:59 -0500

 Just some helpful information:
 
 I can confirm this bug for gdb in CVS on 22 Nov 2005 with an i686 
 running Fedora Core 4 Linux/GNU, kernel version 2.6.13.
 
 The problem occurs in tui_vertical_disassem_scroll, which is called when 
 the user presses the "down arrow" key as described in the bug report.  
 Since we've never seen a source code window yet, the function 
 set_current_source_symtab_and_line has not yet been called.  This causes 
 the call to get_current_source_symtab_and_line to return a 
 symtab_and_line structure which is all zero.  The logic of 
 tui_vertical_disassem_scroll then calls get_frame_pc on 
 deprecated_selected_frame, which is NULL.  get_frame_pc tries to do a 
 NULL dereference, and SEG faults.
 
 To fix the problem, I'm using the following patch.  The main idea is 
 that tui_update_source_window_as_is ignores the symtab struct whenever 
 the first argument is not a SRC_WIN, so we can skip trying to find it in 
 the first place.
 
 Index: gdb/tui/tui-disasm.c
 ===================================================================
 RCS file: /cvs/src/src/gdb/tui/tui-disasm.c,v
 retrieving revision 1.15
 diff -u -r1.15 tui-disasm.c
 --- gdb/tui/tui-disasm.c    1 Nov 2005 17:40:25 -0000    1.15
 +++ gdb/tui/tui-disasm.c    23 Nov 2005 13:12:57 -0000
 @@ -379,16 +379,10 @@
      {
        CORE_ADDR pc;
        tui_win_content content;
 -      struct symtab *s;
        struct tui_line_or_address val;
        int max_lines, dir;
 -      struct symtab_and_line cursal = 
 get_current_source_symtab_and_line ();
  
        content = (tui_win_content) TUI_DISASM_WIN->generic.content;
 -      if (cursal.symtab == (struct symtab *) NULL)
 -    s = find_pc_symtab (get_frame_pc (deprecated_selected_frame));
 -      else
 -    s = cursal.symtab;
  
        /* account for hilite */
        max_lines = TUI_DISASM_WIN->generic.height - 2;
 @@ -397,6 +391,6 @@
  
        val.loa = LOA_ADDRESS;
        val.u.addr = tui_find_disassembly_address (pc, dir);
 -      tui_update_source_window_as_is (TUI_DISASM_WIN, s, val, FALSE);
 +      tui_update_source_window_as_is (TUI_DISASM_WIN, NULL, val, FALSE);
      }
  }
 
 
 Joshua Neuheisel
 jneuheisel@gmail.com
 
 



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