Re: Unable to step over functions in arm-elf binary

[Colin MacDonald <colin_mac2002@yahoo.co.uk>]

OK, so I have a breakpoint on a line that calls a function.  When I hit the breakpoint the backtrace shows this:

#0  CPlatform::RunTestSuite (this=0x207ffb4) at Common/Platform.cpp:113
#1  0x01017db0 in main (argc=17253984, argv=0x0) at OtherFiles/Main.cpp:37

This is fine so far.  Line 113 of platform.cpp calls a function called vs_status.  If I stepi until I first hit vs_status I get the following as the backtrace:

#0  vs_status (pInBuf=0x0) at Common/PlatformIO.cpp:149
#1  0x00000000 in ?? ()

Doesn't look happy.  If I execute another stepi then pInBuf is picked up.  Another few stepi instructions then fills in the backtrace properly:

#0  vs_status (pInBuf=0x207ffb4 "Ôé\006\001\224Ù\006\001ØV\a\001¬\r")
    at Common/PlatformIO.cpp:153
#1  0x010034f8 in CPlatform::RunTestSuite (this=0x207ffb4)
    at Common/Platform.cpp:113
#2  0x01017db0 in main (argc=17253984, argv=0x0) at OtherFiles/Main.cpp:37

which seems fine.

The code in the region of line 2401 in infrun.c:

  if (!frame_id_eq (get_frame_id (get_current_frame ()), step_frame_id)
      && frame_id_eq (frame_unwind_id (get_current_frame ()), step_frame_id))
    {

should
determine whether or not we have stepped into a subroutine and, if so,
will go on to set a breakpoint at the caller's location in the desired
way.  The frame_id_eq call is returning zero, however, so I don't get
the breakpoint.  With frame debug on I get a pile of stuff the
culminates in:

{ frame_id_eq (l={!stack,!code,!special},r={stack=0x207ff68,code=0x10032dc,!special}) -> 0 }

which
makes me think that get_current_frame is returning something
unexpected.  Certainly if I bypass the above test then I get a failure
assertion in
    insert_step_resume_breakpoint_at_caller (get_current_frame ());

I've tried building with -mapcs-frame but it doesn't seem to make any difference.  And that's me into guesswork now.

Colin MacDonald


----- Original Message ----
From: Daniel Jacobowitz <drow@false.org>
To: Colin MacDonald <colin_mac2002@yahoo.co.uk>
Cc: gdb@sourceware.org
Sent: Thursday, 22 February, 2007 1:12:59 PM
Subject: Re: Unable to step over functions in arm-elf binary

On Thu, Feb 22, 2007 at 12:56:04PM +0000, Colin MacDonald wrote:
> I'm using GDB / Insight 6.5.  First attempts with 6.6 appear to show the same behaviour.
> 
> I updated my remote serial server to support $vCont packets as well as the basic $c and $s packets but no joy.

I recommend you single step (using stepi) to the first instruction of
a function you can't "next" over, and try "backtrace".  If it's wrong,
that's your problem.  Keep stepi'ing a bit until you're into the
function body.

Another thing that may be helpful is "set debug infrun 1".


-- 
Daniel Jacobowitz
CodeSourcery





	
	
		
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