1 Some notes to help future porters. Replace 'ARCH' with whatever arch
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
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
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
35 - create these additional files in ARCH/bits/
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
40 kernel_types.h should be created based upon linux asm-ARCH/posix_types.h
42 copy linux asm-ARCH/stat.h to bits/kernel_stat.h
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.
49 - at this point, you should have enough to generate a working HELLO WORLD
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.
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
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.
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_###_###
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
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
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
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
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
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
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.
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.