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Some notes to help future porters. Replace 'ARCH' with whatever arch
you are hacking on.
====================
=== Config Files ===
====================
- create extra/Configs/Config.ARCH
See the other arch files for some good examples. powerpc/sparc/alpha
should be pretty simple templates.
- add ARCH to the 'Target Architecture' list in extra/Configs/Config.in
- Initially you will want to disable shared libraries, since making
the shared library loader work requires you first have basic architecture
support working. Thus you should add HAVE_NO_SHARED and ARCH_HAS_NO_LDSO
to Config.ARCH's HAVE_ELF
====================
=== libc sysdeps ===
====================
(note: if glibc has already been ported to your arch, you can usually just
copy a lot of files from them rather than coding from scratch)
- create libc/sysdeps/linux/ARCH
- copy Makefile and Makefile.arch from libc/sysdeps/linux/i386/
- set CSRC and SSRC to nothing in Makefile.arch for now
- create crt1.S which defines the _start function ... you will probably want
to clear the frame pointer to make gdb happy, and then you will want to call
the funcion __uClibc_main() which takes these parameters:
__uClibc_main(main(), argc, argv, _init(), _fini())
Initially if you wish to make things easier on yourself, you can disable the
UCLIBC_CTOR_DTOR option and just set those two arguments to NULL
glibc generally stores this function in libc/sysdeps/ARCH/elf/start.S
- create these additional files in ARCH/bits/
(template versions can be found in common/bits/ for you to tweak)
endian.h fcntl.h setjmp.h stackinfo.h uClibc_arch_features.h wordsize.h
kernel_types.h should be created based upon linux asm-ARCH/posix_types.h
copy linux asm-ARCH/stat.h to bits/kernel_stat.h
create syscalls.h based upon linux's unistd.h / glibc's sysdeps.h ... really
you just want to define the _syscall[0-6] macros. It is important that
these syscalls should be PIC safe (or you should provide a PIC and non-PIC
version) if you wish to properly support shared libraries.
- at this point, you should have enough to generate a working HELLO WORLD
static binary (see test/silly/*.c files)
- if you want UCLIBC_CTOR_DTOR support, you will need to create crti.S and
crtn.S files which define function prologues/epilogues.
- for a more stable static port, you will need to create these files (and
update the Makefile.arch values accordingly)
__longjmp bsd-_setjmp bsd-setjmp brk clone setjmp syscall vfork
usually these are written in assembler, but you may be able to cheat and
write them in C ... see other ports for more information
====================
=== pthread deps ===
====================
TODO: nptl / linuxthreads / linuxthreads.old
====================
=== ldso sysdeps ===
====================
- enable ldso/shared options in your extra/Configs/Config.ARCH file
- you will need to create the following files in ldso/ldso/ARCH/
dl-debug.h dl-startup.h dl-syscalls.h dl-sysdep.h elfinterp.c resolve.S
- dl-debug.h: define string versions of all the relocations of your arch in the
_dl_reltypes_tab array ... the index should match the actual reloc type, so
if the value of say R_X86_64_PC16 is 13, then "R_X86_64_PC16" better be at
index 13 of the array
- dl-startup.h:
- define the _start function which should call _dl_start which takes just one
parameter ... a pointer to argc (usually on the stack)
- define the GET_ARGV() macro which calculates the value of argv based upon
the parameter passed to _dl_start (usually it's simply just ARGS+1)
- define PERFORM_BOOTSTRAP_RELOC() macro which will handle just the relocs
that the ldso itself will generate
- dl-syscalls.h:
if you wrote your bits/syscalls.h file correctly in the libc step above, you
can simply copy this file from another arch and be done ... otherwise you
will have to define the syscall[0-6] macros again, but this time setting
_dl_errno instead of just errno
- dl-sysdep.h:
misc cruft goes in here ... you want to:
- either define or undefine ELF_USES_RELOCA
- define the INIT_GOT macro
- define MAGIC1 to the EM_### value your ELF arch uses
- define ELF_TARGET to a string name for your arch
- define the do_rem() macro
- define misc ALIGN macro's
- define elf_machine_type_class() macro
- define the inline functions elf_machine_dynamic, elf_machine_load_address,
and elf_machine_relative
glibc stores a bunch of these values in libc/sysdeps/ARCH/dl-machine.h
- elfinterp.c:
define all the relocation functions ... it's best if you just copy from
another arch which uses the same type of relocations (REL or RELA) and
start from there.
- resolve.S:
front end of lazy relocation ... define the _dl_linux_resolve symbol which
is called by a PLT entry which has yet to be setup ... you will want to:
- set up arguments for _dl_linux_resolver()
- call _dl_linux_resolver()
- clean up after call
- jump to function address now stored in PLT
|
