[yocto] [EXTERNAL] Re: Issues adding bare meta toolchain to yocto build

[richard.purdie at linuxfoundation.org]

On Thu, 2019-10-24 at 10:30 -0400, William Mills wrote:
> On 10/24/19 10:02 AM, richard.purdie at linuxfoundation.org wrote:
> > On Thu, 2019-10-24 at 09:43 -0400, William Mills wrote:
> > > Then understand that you will need to supply your own gcc
> > > compiler
> > > helpers and all stdc functions even the ones that port well like
> > > strlen and memcpy.  (Because everyone should embedded their own
> > > unoptimized memcpy in their projects.)
> > 
> > Right, that is by definition baremetal.
> > 
> 
> Well not really.  All the "bare-metal" toolchains I have used come
> with a proper libgcc and some conig of newlib that at least gets you
> usable strlen and memcpy etc.  How much of the rest of it is usable
> on your platform is variable.
> 
> This is true of the toolchain Oliver is pointing at and has been true
> back to 2007 when I was using codesourcery releases.

The baremetal libgcc would be libgcc-initial in OE terms. As for
"baremetal", OE defines that as no library. You can see the options in
this listing:

http://git.yoctoproject.org/cgit.cgi/poky/tree/meta/conf/distro/include

tclibc-baremetal.inc
tclibc-glibc.inc
tclibc-musl.inc
tclibc-newlib.inc

So we support newlib builds but that is different to our definition of
baremetal. So we conflicting usage of terms.

> > You're probably right to have some concerns in that its not a well
> > travelled path. There are libc specifics encoded into libgcc but I
> > can't quite see where they change how gcc behaves other that the
> > default option selection.
> > 
> > Equally there may be something I'm missing.
> > 
> > For full disclosure, gcc is built against linux-libc-headers
> > wherease
> > with baremetal it would be built without headers. I believe that
> > changes the default options gcc uses for compiling but not the way
> > the
> > compiler itself works.
> 
> "baremetal" would be compiled against some config of newlib headers.
> newlib has its own issues and many config choices (you get to pick
> your threading model: none, bad, or hacky).  For TI-RTOS I think we
> rebuild it with a different thread model.

Our baremetal is compiled with no headers. Newlib is effectively like
choosing a different C library, and yes, gcc would be built against its
headers and use it to link against. You would need multiconfig to mix a
newlib and musl/glibc toolchain.

Sorry for the confusion over the terms.

Cheers,

Richard