Freestanding/Baremetal

[Immortalin]

Is it possible to add a compiler option for freestanding/bare metal compilation? (Equivalent GCC flag -ffreestanding )

[norayr]

Hey. I was using it for AVR micros, as well as for nmos6502 computer. In the former case avr-libc provided enough options, in the latter - cc65 had already implemented standard library to work on bare metal computer. Which platform do you need it for?

or may be i did not understand the question good enough.

[Immortalin]

@norayr just standard x86/64

[norayr]

Short search did not unveil for me some answers yet.

Does gcc when used with -ffreestanding produce code that can be booted on a standard x86?

Then, which options do you have for further development? I guess you cannot access filesystems? How does standard output work? When you use write(), the code gcc generates already implements the write system call? Can you use stdio with printf() let's say?

Short answer is yes, it is fairly possible to use voc on a bare metal, moreover, that gcc supports it.
I just never tried using gcc with that flag, didn't even know about it's existence, and need to experiment. Also, I need to understand better the new build system, which @dcwbrown recently implemented.

[Immortalin]

@norayr this page will give you more information: http://wiki.osdev.org/Bare_Bones

[dcwbrown]

Hi.

As Norayr says, this should be possible. OS access is from a fairly
limited range of places:

All operating system requests from user programs and from the run time
system should go through either Platformunix.Mod or Platformwindows.Mod.
I believe memcpy and strcmp are the only two functions that SYSTEM.h
calls directly, and most C compilers should be treating them as
built-ins/intrinsics (i.e. they generate inline code rather than calls
to library code).

Fundamentally you will need to update configure.c and vishap.make in
src/tools/make to add a 'barebones' platform type, and implement
Platformbarebones.Mod. These contain things like memory allocation and
file access. Some of these are referenced in SYSTEM.h or SYSTEM.c and
you will need to provide your own versions (e.g. OSAllocate). Others are
used by standard modules like Files.Mod (e.g. OpenRO and OpenRW).

The startup code is generated by the compiler when you pass -m: it
generates an 'int main(int argc, char **argv)' that calls all the Oberon
run time system initialisation code (mainly type setup) ahead of the
actual code of the main module. One approach woul be to provide your own
C startup code that calls main.

When voc calls gcc, it looks for an environment variable called CFLAGS
and includes its value in the parameters passed to gcc, so it is
possible to set and/or override compiler and linker options this way.

I'm sure there will be things we haven't though of, but does that sound
roughly like what you would be looking for?

-- Dave.

On 2016-07-26 15:09, Immortalin wrote:

@norayr [1] this page will give you more information: http://wiki.osdev.org/Bare_Bones [2]

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[2] http://wiki.osdev.org/Bare_Bones
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