Re: info frame ADDR internal error

[Pedro Alves <pedro@codesourcery.com>]

:-(

Was going to commit the patch, but then I tried it on x86 (I was on x86-64 before) ...

 (top-gdb) bt
 #0  main (argc=1, argv=0xffffd524) at ../../src/gdb/gdb.c:28

 (top-gdb) info frame 1
 Stack frame at 0x1:
  eip = 0x0; saved eip 0xf7f26f59

 Breakpoint 1, internal_error (file=0x8314a4f "../../src/gdb/valops.c", line=662,
     string=0x8314a19 "%s: Assertion `%s' failed.") at ../../src/gdb/utils.c:972
 972       va_start (ap, string);

 (top-gdb) bt
 #0  internal_error (file=0x8314a4f "../../src/gdb/valops.c", line=662, string=0x8314a19 "%s: Assertion `%s' failed.")
     at ../../src/gdb/utils.c:972
 #1  0x08116c44 in value_fetch_lazy (val=0x883f960) at ../../src/gdb/valops.c:662
 #2  0x0810b766 in value_contents_all (value=0x883f960) at ../../src/gdb/value.c:375
 #3  0x081efd43 in frame_register_unwind (frame=0x8421250, regnum=5, optimizedp=0xffc759f4, lvalp=0xffc759e8,
     addrp=0xffc759f0, realnump=0xffc759ec, bufferp=0xffc75a40 "...") at ../../src/gdb/frame.c:603
 #4  0x081eff19 in frame_unwind_register (frame=0x8421250, regnum=5, buf="...") at ../../src/gdb/frame.c:639
 #5  0x081eff3d in get_frame_register (frame=0x84212e4, regnum=5, buf="...") at ../../src/gdb/frame.c:647
 #6  0x0809c2b7 in i386_frame_cache (this_frame=0x84212e4, this_cache=0x84212e8) at ../../src/gdb/i386-tdep.c:1306
 #7  0x0809c47e in i386_frame_this_id (this_frame=0x84212e4, this_cache=0x84212e8, this_id=0x8421304)
     at ../../src/gdb/i386-tdep.c:1369
 #8  0x081ef2cb in get_frame_id (fi=0x84212e4) at ../../src/gdb/frame.c:261
 #9  0x081f194d in get_frame_base (fi=0x84212e4) at ../../src/gdb/frame.c:1666
 #10 0x0814cd44 in frame_info (addr_exp=0x83f5133 "1", from_tty=1) at ../../src/gdb/stack.c:995
 #11 0x080d51b7 in do_cfunc (c=0x84187c0, args=0x83f5133 "1", from_tty=1) at ../../src/gdb/cli/cli-decode.c:67

Here's the offender:

 int
 value_fetch_lazy (struct value *val)
 {
   gdb_assert (value_lazy (val));
   allocate_value_contents (val);
   if (VALUE_LVAL (val) == lval_memory)
     {
       CORE_ADDR addr = VALUE_ADDRESS (val) + value_offset (val);
       int length = TYPE_LENGTH (check_typedef (value_enclosing_type (val)));
 
       if (length)
 	read_memory (addr, value_contents_all_raw (val), length);
     }
   else if (VALUE_LVAL (val) == lval_register)
     {
       struct frame_info *frame;
       int regnum;
       struct type *type = check_typedef (value_type (val));
       struct value *new_val = val, *mark = value_mark ();
 
       /* Offsets are not supported here; lazy register values must
 	 refer to the entire register.  */
       gdb_assert (value_offset (val) == 0);
 
       while (VALUE_LVAL (new_val) == lval_register && value_lazy (new_val))
 	{
 	  frame = frame_find_by_id (VALUE_FRAME_ID (new_val));
                  ^^^^^^^^^^^^^^^^
 	  regnum = VALUE_REGNUM (new_val);
 
 	  gdb_assert (frame != NULL);
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^

 (top-gdb) p VALUE_FRAME_ID (new_val)
 $1 = {stack_addr = 1, code_addr = 0, special_addr = 0, stack_addr_p = 1, code_addr_p = 1, special_addr_p = 0}

The new frame that create_new_frame created, isn't linked in the
regular ( current_frame->... ) frame chain, it lives in its own chain,
so this frame_find_by_id call isn't going to find it, unless you
get lucky.

This reinforces the bad things I was saying about create_new_frame.

Any suggestions on how this could be fixed?

Before we go farther, is this a valid use case at all?  Could
we rip this piece of parse_frame_specification_1 out instead?  It's been
broken for years now --- I can reproduce the original internal error
on gdb-6.0:

 >./gdb ./gdb
 GNU gdb 6.0
 Copyright 2003 Free Software Foundation, Inc.
 ...
 (top-gdb) b main
 Breakpoint 3 at 0x8077aa4: file ../../gdb-6.0/gdb/gdb.c, line 30.
 (top-gdb) r
 Starting program: /home/pedro/gdb/ancient/build-6.0/gdb/gdb
 Breakpoint 3, main (argc=1, argv=0xffd15254) at ../../gdb-6.0/gdb/gdb.c:30
 30        memset (&args, 0, sizeof args);
 (top-gdb) info frame 1
 Stack frame at 0x1:
  eip = 0x0; saved eip
 ../../gdb-6.0/gdb/dwarf2-frame.c:518: internal-error: dwarf2_frame_cache: Assertion `fde != NULL' failed.

Note that "info frame ADDR" and "frame ADDR" do look for a frame in
the regular chain that matches ADDR, before resorting to hacking up
a new one with create_new_frame.

-- 
Pedro Alves