Subject: Re: tracking program counter / assembling objdump output
To: None <port-m68k@NetBSD.org>
From: None <SigmFSK@aol.com>
Date: 10/12/2006 06:50:44
In a message dated 10/12/2006 2:45:34 A.M. Eastern Standard Time,
Because it isn't possible.
The disassembler cannot know whether constants should be absolute numbers,
diffences between addresses, or addresses themselves. So when you
reassemmble the output you'll end up with incorrect code.
Thanks David. I followed agrier's suggestion last night to ask the binutils
mailing list and got a similar response. I still think it would be neat to
make a converter from objdump output to gcc-assemblable source and have it
ask for human help when needed, but the more I think about - not neat enough to
actually go through the work of doing it.
> It appears that the objdump output is quite similar to, but deliberately
> different from, the assembly created from compiling a c program with "gcc
> Is there a mechanism to convert the objdump disassembly output to an
> assemblable form?
Apart from doing this by hand, no.
> Or is that a deliberate objdump decision to have the output
> different, as my desire is inherently unworkable,
It was a deliberate decision but the motive was to make disassembler's
output be useful to people who want to examine the contents of a binary
file, not to allow re-assembly. To this end, more information is
presented to the user than is needed to just re-assemble the
> as modifying the disassembly
> would change all the branch offsets and cause everything to break?
No, the real problem is coping with relocations. The disassembled
output of a file is not just the textual disassembly, but also the
relocations that are associated with that disassembly. You would need
some way to re-install those relocations back into the assembler source,
possibly regenerating local labels as you go. A difficult task.