Relaxation and .debug_loc section

[Michael Eager]

Andreas Schwab wrote:
> Michael Eager <eager@eagercon.com> writes:
> 
>> When the relaxation pass shrinks the code, these offsets
>> point to the wrong locations.  I've looked through other
>> targets to see if there is anything which looks like it
>> fixes up the .debug_loc section after relaxation, but
>> I haven't found anything.
> 
> I think if you want to do linker relaxing you have to tell the assembler
> not to resolve such relocations.

There's no way to do that.   The offsets are simple expressions.
The assembler converts them to integer values.

The entries in the .debug_loc table look like the following:
$LLST2:
	.4byte	$LFB4-$Ltext0         <==
	.4byte	$LCFI8-$Ltext0        <==
	.2byte	0x1
	.byte	0x51
	.4byte	0x0
	.4byte	0x0

The values marked <== are offsets into the .text section and
need to be modified when the size of the section changes.

I'm writing the code to step through the .debug_loc data
and fix up these offsets.  It's not complex, I just didn't
want to duplicate existing code.

Unfortunately, all of the relaxation code is target-dependent
code.  Much of it could be common routines, with the target
specific code deciding which addresses need to be relaxed.

-- 
Michael Eager	 eager@eagercon.com
1960 Park Blvd., Palo Alto, CA 94306  650-325-8077