This is the mail archive of the newlib@sources.redhat.com mailing list for the newlib project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: porting newlib


Matt Broadstone wrote:
Well you see, the reason I chose to try using newlib is because the OS this
is intended for is non-*ix (I probably would have used glibc otherwise
right?) As for right now I would simply like to implement the basic
syscalls, and add new ones from there. So what I have done so far is:

- make a new directory in libc/sys for the os
- add a sys directory inside of it with a "syscall.h"
- add files to the previous directory (libc/sys/my-os) implementing the
basic syscalls (open.c, read.c, write.c - you get the idea, but not kill.c,
exec.c, fork.c because they are not implemented in this OS in favor of other
methods, I am assuming since I set syscall_dir to syscalls it will fill in a
stub for these that I do not implement?)

This is mostly correct, however, you won't get default stubs. If they don't apply you should put in your own default stubs for the missing syscalls (see the libgloss/libnosys directory). They are relatively simple.


- modify configure.host to recognize my os, set the sys_dir to that folder,
and syscall_dir to ??? (syscall_dir=syscalls?)


Yes. Set syscall_dir=syscalls. Make sure your syscalls start with an underscore (e.g. open.c should implement _open).


that seems to be as much as I have gotten. I am completely glossing over
libgloss right now just to get newlib working. Am I on the right track? Are
there any specific files I am forgetting to change?



You won't need to alter libgloss. You are on the right track.


_______________________________

Matt Broadstone
Tel: (401) 232-4498
Cell: (301) 641-6893
E-mail: mbroadst@bryant.edu


-----Original Message-----
From: Jeff Johnston [mailto:jjohnstn@redhat.com] Sent: Tuesday, May 11, 2004 5:50 PM
To: Matt Broadstone
Subject: Re: porting newlib


Matt Broadstone wrote:

Thank you so much, very informative. The specific port I am trying to
accomplish is for an OS that runs on ix86, so I'm not sure that I need to

do


much regarding the machine dir, setjmp etc. and in which case I think I do
need to work specifically with the sys_dir, and sys_call dirs as the port

is


an os port not an architecture port. I understand this is a rather strange
task, but if you have any insight it'd be much appreciated.




Yes, you are right. You have to add a sys directory. At a minimum, you
have to supply the assembly code for the newlib syscalls on your OS. This is a relatively small set (see the libgloss/fr30/syscalls.c for the set). If you


ever feel you might add other platforms, you can do like sys/linux did and
have a machine/i386 directory. This allows you to add other platforms in the
future.


Now, if you have a relatively robust OS, you may want more than the basic
newlib syscall set. If your syscall set is similar to linux, you have the option
of stealing code from the sys/linux directory for POSIX routines that use the syscalls. Note that sys/linux is LGPL and if you take code from there your library will end up LGPL too. Vanilla newlib is BSD-like. The licensing
issue may or may not sway your decision.


Depending how similar your OS is to Linux regarding types of syscalls, you
could try an experiment and change the syscall code in libc/sys/linux/machine/i386/syscall.h. Then try building newlib for i686-pc-linux-gnu (configure with --with-newlib). Link your executable and
try it out on your OS. If this works and you are ok with having an LGPL
license, there might be an opportunity to share the code which will save you effort.


-- Jeff J.


_______________________________

Matt Broadstone

Tel: (401) 232-4498
Cell: (301) 641-6893
E-mail: mbroadst@bryant.edu




-----Original Message-----
From: newlib-owner@sources.redhat.com
[mailto:newlib-owner@sources.redhat.com] On Behalf Of Jeff Johnston
Sent: Tuesday, May 11, 2004 4:20 PM
To: Matt Broadstone
Cc: newlib@sources.redhat.com
Subject: Re: porting newlib

Matt Broadstone wrote:


When the build process builds for say "arc" (for example), the defined
syscall_dir is the directory "syscalls" in "libc" which are all stubs,
correct? However there is another file called "syscalls.c" inside the arc
sys_dir. I have tried to look into what was done for linux, but linux has
nothing to do with syscalls.... I am very lost here obviously, but there
seems to be no documentation regarding this stuff? Please excuse my
ignorance :)




Matt,

A basic port needs to alter a number of files and add some directories.

  1. Add a subdirectory to the newlib/libc/machine directory for your
platform.
     In this directory you need to have a setjmp/longjmp implementation.
This
     is required because setjmp/longjmp usually is assembler.  Look at

the


libc/machine/fr30 directory and copy/modify the files in there.

  2. Edit newlib/libc/include/machine/ieeefp.h
     This defines the ieee endianness for your platform.  The compiler
should
     be defining something that identifies your machine.  In some cases,
the
     endianness may be a compiler-option so you may have to check another
     define in addition to your platform identifier.  See examples in the
     file.

  3. Edit newlib/libc/include/machine/setjmp.h
     You need to specify the setjmp buffer characteristics to match up

with


     your setjmp/longjmp implementation.  This is just the size of the
     setjmp buffer.  See file for examples.

  4. Edit newlib/libc/include/sys/config.h
     This has various defines as needed.  Mostly, it defines some max
     values.  There are defaults that may apply to your platform in which
case
     you needn't do anything.

  5. Edit configure.host
     You need to add your configuration so newlib can recognize it.  You
should
     specify your new machine directory for your platform via the
machine_dir
     variable.  If needed, you can add special newlib compile flags.  The
     sys_dir is for OS stuff so you won't need to alter that.  Older
platforms
     used the sys_dir to implement syscalls but this is not correct and

is


     a historical nuisance.  The syscall_dir is a choice, but I recommend
as a
     default to specify syscall_dir=syscalls. Read the comments in
     newlib/libc/include/reent.h for an explanation of choices.

  6. Add a machine subdirectory to libgloss
     You need to add a bsp for your platform.  This is the minimum set of
     syscalls needed by newlib and any linker scripts needed.  This

varies


     from board to board (it can also be a simulator).  See the
     mn10300 or fr30 for examples. You will need
     to edit configure.in and regenerate configure so it will build your
     new files.  By default you get libnosys which gives you a set of
     default syscall stubs.  The majority of the stubs just return

failure.


You still need to supply an __exit routine. This can be as simple

as


generating an exception to stop the program.

  7. Possibly override header files
     If you need to override any default machine header files, you can
     add a machine directory to newlib/libc/machine/<YOUR_MACHINE_DIR>
     Header files in that subdirectory will overwrite the defaults found
     in newlib/libc/include/machine.  You will likely not need to do

this.


This assumes you have already handled adding your new configuration to
the top directory files.


Now linux is a different animal. It is an OS that has an extensive set
of syscalls. If you look in the newlib/libc/sys/linux directory, you will

find


a number of syscalls there (e.g. see io.c). There is a set of basic syscall


macros that are defined for the particular platform. For the x86, you

will


find these macros defined in newlib/libc/sys/linux/machine/i386/syscall.h file.
At the moment, linux support is only for x86. To add another platform, the syscall.h file would have to be supplied for the new platform plus some
other platform-specific files would need to be ported as well.


I hope this helps.

-- Jeff J.






Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]