as / ld problem/question

Shane Stevens shane@bluetongue.com
Mon Jan 20 22:06:00 GMT 2003


Hi all,
I am new to this messageboard and the gnu/binutils environment, so
please forgive me if this question is obvious.

Here is the basic idea of the pipeline I would like to write.

I work with embedded systems with small memory footprints and so I would
like to offline compile and partially link data such that it resides in
a nice contiguous block that is relocatable.

I will then write a small relocation loader which will take a section
table with a relocation offset table and run-time patch addresses upon
load.  I can't use the gnu compiler for the embedded run-time code
because there are already compilers/linkers for for me to use, so that
means I need to be able to write my own relocation code.

So in a nutshell: I want to have a pipeline that takes a bunch of
assembled data files, links them together and emits a relocatable ELF
file.  I will write a tool on top of the final output that strips the
file down to what I specifically need.  I will write a run-time loader
with relocation to load the file at an arbitrary address.

Rather than reinvent the wheel and write a relocatable assembler/linker
for the purposes of compiling data (not code), I would like to us 'as'
and 'ld'.  Again, I might add this is my first experience with gnu.  I
normally code with Microsoft products. :|

I have downloaded the cygwin package and after a few tests I have found
that 'ld' does indeed support relocatable hunks so all the information I
need is in the output.  However, the output files are quite verbose,
even with most information stripped out via the command line options,
and besides I need to get the files as small as possible, so I intend to
write my own stripping tool which gets the file down to exactly what I
need.

Some problems I have encountered thus far are:
1. I can't seem to output an ELF file from the Win32 'ld' even after
putting '-format -elf32-little' on the 'ld' command line.  This is the
most frustrating.  'objcopy' seems to do it, but I need both little/big
endian assembled/linked output and I can't seem get all combinations.
The linker SAYS it can output ELF files. 2. It would appear that there
is a fair amount of documentation on the .ELF format, but I can't find
ANY read/write libraries. 3. I can't seem to find documentation or code
on the GNU relocation method.  'dllopen' is the function I want I think.


Any advice you might have would be greatly appreciated.


Shane Stevens
Lead Programmer
bluetongue
www.bluetongue.com





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