Subversion Repositories openrisc_me

These notes were written to record the current state of this code.

Much of it was written during the investigation work.

At present this stuff is only partially functional. Do not assume

anything works. In particular things like constructor/destructors and

init/fini sections have not been fully implemented.

Initial Investigations

======================

Attempts to build a simple shared library using the existing

tools. Command line is something like:

xxx-gcc -shared -o libfoo.so foo.so

arm-elf                 no - includes crt0 which fails to find main() etc.

thumb-elf               no - includes crt0 which fails to find main() etc.

i686-pc-linux-gnu       yes

i386-elf                no - tries to build program

mn10300                 no - tries to build program

powerpc-eabi            no - implicit ref to libc.so

sh-elf                  no - tries to build program

sparclite               no - fails to find crtn.o

mips-tx39-elf           yes - but seriously mangles PHDR DYNAMIC section

mips66vr4300-elf        yes - but seriously mangles PHDR DYNAMIC section

Building new Toolchains

=======================

Given the poor results from our standard toolchains, it was decided to

try and use Linux-targeted toolchains, which are guranteed to have the

necessary support.

These builds all use bindutils-2.1.1, gcc-2.95.2 and gdb-5.0.

arm-unknown-linux-gnu   build of libgcc fails looking for asm/unistd.h

All MIPS Linux toolchains use collect2 constructors, so no priorities.

MIPS support also requires PIC code support, which needs HAL

changes. In this case it is fairly easy since the assembler does a lot

of the conversion for us but there are still some things that need

fixing.

MIPS BSD toolchains fail building libgcc, but adding files from

openbsd sources allows these to build. However, these then fail to

build proper PIC code and omit some features.

PowerPC toolchains need to use the full ABI, not the ebedded one, with

TOCs and all the trimmings. This requires major changes to the

HAL. Or maybe not - not too sure about this one.

Since we are having so much difficulty getting any of these to work,

try to get it running on the i686-pc-linux-gnu synthetic target, since

we know that works.

Synthetic Target

================

To enable a progam to be capable of loading a shared library it must

include a DYNAMIC section. This includes the symbol, string and hash

tables needed to satisfy any references from the loaded library back

to the executable. The only way I have so far worked out to make this

happen is to link the executable against a dynamic library. This needs

the -Wl,-static flag to be removed.

A simple library, libdlforce.so has been created to make this

happen. It is not even necessary for the progam to call into the

library, just having it on the command line is enough.

Generation of usable libraries and executables is very sensitive to

the exact form of the linker scripts used.

src/dynamic.ld has been replaced by a very lightly edited copy of

i686-pc-linux-gnu/H-i686-pc-linux-gnu/i686-pc-linux-gnu/lib/ldscripts/elf_i386.xs

To make the main executable work correctly the i386.dynamic.ld script

in this directory must be copied over target.ld before building any

programs. I have not yet worked out what the problems are, but the

original target.ld causes programs built for dynamic loading to

SIGSEGV in ld.so.

If we try to use the POSIX package, we get spurious calls to

pthread_mutex_unlock() from somewhere in the Linux runtime. This may

be a result of using a different linker script, however.

Retesting toolchains

====================

Having got the synthetic target sort-of working, now go back and see

what happens when configuring each of our standard toolchains for the

loader.

arm-elf         - build of shared library with external references

                  result in "undefined reference to `fee'".

mips-tx39-elf   - mangles DYNAMIC section as before.

powerpc-eabi    - Compiler selects a libgcc.a that contains references

                  to "abort" and "strcmp". With these defined we get

                  sensible looking libraries.