Tue May 11 21:00:00 GMT 2004
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 :)
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
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.
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