1Some notes to help future porters.  Replace 'ARCH' with whatever arch
2you are hacking on.
3
4====================
5=== Config Files ===
6====================
7- create extra/Configs/Config.ARCH
8   See the other arch files for some good examples.  powerpc/sparc/alpha
9   should be pretty simple templates.
10- add ARCH to the 'Target Architecture' list in extra/Configs/Config.in
11- Initially you will want to disable shared libraries, since making
12   the shared library loader work requires you first have basic architecture
13   support working.  Thus you should add ARCH_HAS_NO_SHARED and
14   ARCH_HAS_NO_LDSO to Config.ARCH's TARGET_ARCH
15- When static pie support is added this TARGET_arch can be appended to the
16   list in extra/Configs/Config.in
17
18====================
19=== libc sysdeps ===
20====================
21(note: if glibc has already been ported to your arch, you can usually just
22       copy a lot of files from them rather than coding from scratch)
23- create libc/sysdeps/linux/ARCH
24- copy Makefile and Makefile.arch from libc/sysdeps/linux/i386/
25- set CSRC and SSRC to nothing in Makefile.arch for now
26
27- create crt1.S which defines the _start function ... you will probably want
28  to clear the frame pointer to make gdb happy, and then you will want to call
29  the funcion __uClibc_main() which takes these parameters:
30   __uClibc_main(main(), argc, argv, _init(), _fini())
31  Initially if you wish to make things easier on yourself, you can disable the
32  UCLIBC_CTOR_DTOR option and just set the init/fini arguments to NULL.
33  glibc generally stores this function in libc/sysdeps/ARCH/elf/start.S
34
35- create these additional files in ARCH/bits/
36
37  (template versions can be found in common/bits/ for you to tweak)
38  endian.h  fcntl.h  setjmp.h  stackinfo.h  uClibc_arch_features.h  wordsize.h
39
40  kernel_types.h should be created based upon linux asm-ARCH/posix_types.h
41
42  copy linux asm-ARCH/stat.h to bits/kernel_stat.h
43
44  create syscalls.h based upon linux's unistd.h / glibc's sysdeps.h ... really
45  you just want to define the _syscall[0-6] macros.  It is important that
46  these syscalls should be PIC safe (or you should provide a PIC and non-PIC
47  version) if you wish to properly support shared libraries.
48
49- at this point, you should have enough to generate a working HELLO WORLD
50  static binary
51
52- if you want UCLIBC_CTOR_DTOR support, you will need to create crti.S and
53  crtn.S files which define function prologues/epilogues.
54
55- for a more stable static port, you will need to create these files (and
56  update the Makefile.arch values accordingly)
57    __longjmp  bsd-_setjmp  bsd-setjmp  brk  clone  setjmp  syscall  vfork
58  usually these are written in assembler, but you may be able to cheat and
59  write them in C ... see other ports for more information
60
61- Once static and pie executables are stable, static-pie support can be
62  added by modifying crt1.S to calculate the address that the kernel loaded
63  the main elf. Once the elf load address is found, call reloc_static_pie to
64  perform all the dynamic relocations normally handled by ldso. This new
65  code should be placed at the begining of _start and surrounded by defines
66  so that it is only compiled into rcrt1.o and not the static or shared
67  versions. This is usually done by using the special L_rcrt1 preprocessor
68  define. i386 and x86_64 have good reference implementations.
69
70====================
71=== ldso sysdeps ===
72====================
73- elf.h - presumably you've already taught binutils all about the random ELF
74  relocations your arch needs, so now you need to make sure the defines exist
75  for uClibc.  make sure the EM_### define exists and all of the R_###_###
76  reloc defines.
77
78- enable ldso/shared options in your extra/Configs/Config.ARCH file
79- you will need to create the following files in ldso/ldso/ARCH/
80  dl-startup.h  dl-syscalls.h  dl-sysdep.h  elfinterp.c  resolve.S
81
82- dl-startup.h:
83  - define the _start function which should call _dl_start which takes just one
84    parameter ... a pointer to argc (usually on the stack)
85    glibc stores this function in sysdeps/ARCH/dl-machine.h as RTLD_START
86  - define the GET_ARGV() macro which calculates the value of argv based upon
87    the parameter passed to _dl_start (usually it's simply just ARGS+1)
88  - define PERFORM_BOOTSTRAP_RELOC() macro which will handle just the relocs
89    that the ldso itself will generate
90
91- dl-syscalls.h:
92  if you wrote your bits/syscalls.h file correctly in the libc step above, you
93  can simply copy this file from another arch and be done ... otherwise you
94  will have to define the syscall[0-6] macros again, but this time setting
95  _dl_errno instead of just errno
96
97- dl-sysdep.h:
98  misc cruft goes in here ... you want to:
99  - either define or undefine ELF_USES_RELOCA
100  - define the INIT_GOT macro
101  - define MAGIC1 to the EM_### value your ELF arch uses
102  - define ELF_TARGET to a string name for your arch
103  - define the do_rem() macro
104  - define misc ALIGN macro's
105  - define elf_machine_type_class() macro
106  - define the inline functions elf_machine_dynamic, elf_machine_load_address,
107    and elf_machine_relative
108  glibc stores a bunch of these values in sysdeps/ARCH/dl-machine.h
109
110- elfinterp.c:
111  define all the relocation functions ... it's best if you just copy from
112  another arch which uses the same type of relocations (REL or RELA) and
113  start from there.
114
115- resolve.S:
116  front end of lazy relocation ... define the _dl_linux_resolve symbol which
117  is called by a PLT entry which has yet to be setup ... you will want to:
118  - set up arguments for _dl_linux_resolver()
119  - call _dl_linux_resolver()
120  - clean up after call
121  - jump to function address now stored in PLT
122  glibc stores this function in sysdeps/ARCH/dl-trampoline.S
123
124- utils/ldd.c - if you want support for ldso cache files (spoiler: you do),
125  then you'll need to teach ldd a little.  generally, the fallback code
126  should be smart and "just work", but you should be explicit.  just pop
127  it open and add an appropriate ifdef for your arch and set MATCH_MACHINE()
128  and ELFCLASSM.  there are plenty examples and you're (hopefully) smart.
129
130====================
131===  Misc Cruft  ===
132====================
133- MAINTAINERS - presumably you're going to submit this code back to mainline
134  and since you're the only one who cares about this arch (right now), you
135  should add yourself to the toplevel MAINTAINERS file.  do it.
136