rtems/doc/FAQ/debug.texi

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@c  COPYRIGHT (c) 1988-2002.
@c  On-Line Applications Research Corporation (OAR).
@c  All rights reserved.
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@node Debugging Hints, Executable Size, , Top

@chapter Debugging Hints
@ifinfo
@menu
* Executable Size::
* Malloc::
* How do I determine how much memory is left?::
* How do I convert an executable to IEEE-695?::
@end menu
@end ifinfo

The questions in this category are hints that can ease debugging.


@node Executable Size, Why is my executable so big?, Debugging Hints, Debugging Hints

@section Executable Size
@ifinfo
@menu
* Why is my executable so big?::
@end menu
@end ifinfo


@node Why is my executable so big?, Malloc, Executable Size, Executable Size

@subsection Why is my executable so big?

There are two primary causes for this.  The most common is that
you are doing an @code{ls -l} and looking at the actual file
size -- not the size of the code in the target image.  This
file could be in an object format such as ELF or COFF and
contain debug information.  If this is the case, it could
be an order of magnitude larger than the required code space.
Use the strip command in your cross toolset to remove debugging
information.

The following example was done using the i386-rtems cross toolset
and the pc386 BSP.  Notice that with symbolic information included
the file @code{hello.exe} is almost a megabyte and would barely fit
on a boot floppy.  But there is actually only about 93K of code
and initialized data.  The other 800K is symbolic information
which is not required to execute the application.

@example
$ ls -l hello.exe
-rwxrwxr-x    1 joel     users      930515 May  2 09:50 hello.exe
$ i386-rtems-size hello.exe
   text	   data	    bss	    dec	    hex	filename
  88605	   3591	  11980	 104176	  196f0	hello.exe
$ i386-rtems-strip hello.exe
$ ls -l hello.exe
-rwxrwxr-x    1 joel     users      106732 May  2 10:02 hello.exe
$ i386-rtems-size hello.exe
   text	   data	    bss	    dec	    hex	filename
  88605	   3591	  11980	 104176	  196f0	hello.exe
@end example

Another alternative is that the executable file is in an ASCII
format such as Motorola Srecords.  In this case, there is
no debug information in the file but each byte in the target
image requires two bytes to represent.  On top of that, there
is some overhead required to specify the addresses where the image
is to be placed in target memory as well as checksum information.
In this case, it is not uncommon to see executable files
that are between two and three times larger than the actual
space required in target memory.

Remember, the debugging information is required to do symbolic
debugging with gdb.  Normally gdb obtains its symbolic information
from the same file that it gets the executable image from.  However,
gdb does not require that the executable image and symbolic
information be obtained from the same file.  So you might
want to create a @code{hello_with_symbols.exe}, copy that
file to @code{hello_without_symbols.exe}, and strip
@code{hello_without_symbols.exe}.  Then gdb would have to
be told to read symbol information from @code{hello_with_symbols.exe}.
The gdb command line option @code{-symbols} or command
@code{symbol-file} may be used to specify the file read
for symbolic information.



@node Malloc, Is malloc reentrant?, Why is my executable so big?, Debugging Hints

@section Malloc
@ifinfo
@menu
* Is malloc reentrant?::
* When is malloc initialized?::
@end menu
@end ifinfo


@node Is malloc reentrant?, When is malloc initialized?, Malloc, Malloc

@subsection Is malloc reentrant?

Yes.  The RTEMS Malloc implementation is reentrant.  It is
implemented as calls to the Region Manager in the Classic API.


@node When is malloc initialized?, How do I determine how much memory is left?, Is malloc reentrant?, Malloc

@subsection When is malloc initialized?

During BSP initialization, the @code{bsp_libc_init} routine
is called.  This routine initializes the heap as well as
the RTEMS system call layer (open, read, write, etc.) and
the RTEMS reentrancy support for the Cygnus newlib Standard C
Library.

The @code{bsp_libc_init} routine is passed the size and starting
address of the memory area to be used for the program heap as well
as the amount of memory to ask @code{sbrk} for when the heap is
exhausted.  For most BSPs, all memory available is placed in the
program heap thus it can not be extended dynamically by calls to
@code{sbrk}.


@node How do I determine how much memory is left?, How much memory is left in the RTEMS Workspace?, When is malloc initialized?, Debugging Hints

@section How do I determine how much memory is left?
@ifinfo
@menu
* How much memory is left in the RTEMS Workspace?::
* How much memory is left in the Heap?::
@end menu
@end ifinfo

First there are two types of memory: RTEMS Workspace and Program Heap.
The RTEMS Workspace is the memory used by RTEMS to allocate control
structures for system objects like tasks and semaphores, task
stacks, and some system data structures like the ready chains.
The Program Heap is where "malloc'ed" memory comes from.

Both are essentially managed as heaps based on the Heap Manager
in the RTEMS SuperCore.  The RTEMS Workspace uses the Heap Manager
directly while the Program Heap is actually based on an RTEMS Region
from the Classic API.  RTEMS Regions are in turn based on the Heap
Manager in the SuperCore.


@node How much memory is left in the RTEMS Workspace?, How much memory is left in the Heap?, How do I determine how much memory is left?, How do I determine how much memory is left?

@subsection How much memory is left in the RTEMS Workspace?

An executive workspace overage can be fairly easily spotted with a
debugger.  Look at _Workspace_Area.  If first == last, then there is only
one free block of memory in the workspace (very likely if no task
deletions).  Then do this:

(gdb) p *(Heap_Block *)_Workspace_Area->first
$3 = @{back_flag = 1, front_flag = 68552, next = 0x1e260, previous = 0x1e25c@}

In this case, I had 68552 bytes left in the workspace.


@node How much memory is left in the Heap?, How do I convert an executable to IEEE-695?, How much memory is left in the RTEMS Workspace?, How do I determine how much memory is left?

@subsection How much memory is left in the Heap?

The C heap is a region so this should work:

(gdb) p *((Region_Control *)_Region_Information->local_table[1])->Memory->first
$9 = @{back_flag = 1, front_flag = 8058280, next = 0x7ea5b4,
  previous = 0x7ea5b0@}

In this case, the first block on the C Heap has 8,058,280 bytes left.


@node How do I convert an executable to IEEE-695?, , How much memory is left in the Heap?, Debugging Hints

@section How do I convert an executable to IEEE-695?

This section is based on an email from Andrew Bythell
<abythell@@nortelnetworks.com> in July 1999.

Using Objcopy to convert m68k-coff to IEEE did not work.  The new IEEE
object could not be read by tools like the XRay BDM Debugger.

The exact nature of this problem is beyond me, but I did narrow it down to a
problem with objcopy in binutils 2-9.1.  To no surprise, others have
discovered this problem as well, as it has been fixed in later releases.

I compiled a snapshot of the development sources from 07/26/99 and
everything now works as it should.  The development sources are at
@uref{http://sourceware.cygnus.com/binutils} (thanks Ian!)

Additional notes on converting an m68k-coff object for use with XRay (and
others):

@enumerate


@item The m68k-coff object must be built with the -gstabs+ flag.  The -g flag
alone didn't work for me.

@item Run Objcopy with the --debugging flag to copy debugging information.

@end enumerate