[yocto] Need clarification on some terms

[Bill Traynor]

On Wed, Jun 12, 2013 at 7:16 AM, <michael at cubic.org> wrote:

> > "Cross-Development Toolchain: A collection of software development tools
> > and
> > utilities that allow you to develop software for targeted architectures."
> > Is
> > that different from the toolchain that bitbake builds in the beginning,
> > and
> > then uses to build the image? If so, what is it?
>
> A "cross development toolchain" is a toolchain that runs on an
> architecture (cpu+os+libc) that is different from the architecture it
> generates code for. That can even be a toolchain running on an IA64-Linux
> machine generating object-code for an IA32-Linux machine.
>
> > "Following is a list of toolchain recipes..." This is followed by
> > gcc-cross-initial, gcc-cross-intermediate, gcc-cross. All three of these
> > things say that the toolchain runs on the host and is used to build
> > software
> > for the target. So why are there three of them? What are the differences
> > among them?
>
> The gcc must be build multiple times when you bootstrap it.
> For building the gcc you need to build the libc and therefor you need to
> build the linux kernel headers and therefor you need the gcc. Oops.
>
> Thats why you first build a gcc only with c support and no libc first.
> Use that to generate the kernel headers, then build the initial libc and
> then another gcc with libc support and all the frontends you need
> (c,c++,java,fortran,..). Why there is the gcc-cross-intermediate I am not
> shure, but there will be a reason and another one can clarify that.
>
> > It also says that each one is a "native" package. In my
> > experience, a "native" toolchain has always meant a toolchain that
> > produces
> > code for the same machine that the toolchain runs on, while a "cross"
> > toolchain produces code for a different machine. That's obviously not
> what
> > "native" means in this context, so what does it mean?
>
> In terms of openembedded a "native" package is a package that contains
> code that is intended to run on the build machine (your workstation). The
> cross-compiler runs on your build-machine to produce code for your
> target-machine. Thats why it is a "native" package. And there are a lot
> more "native" packages than only the compiler.
>
> > The documentation makes frequent references to "the SDK" without ever
> > defining it. I know what it means generically, but what is it in the
> Yocto
> > context? And why does the SDK involve yet another set of three
> toolchains?
> > (Oh, and why is one of them called "canadian"?)
>
> A canadian-cross is a term from the compiler stuff, not specific to the
> Yocto Project or Poky or Openembedded.
> Building a canadian-cross is the process of build a toolchain on
> architecture A that runs on architecture B and produces object-code for
> architecture C. An example is building a gcc on an IA32 architecture, that
> will run on an ARM, producing code for an M68K. Yes, that does make sence,
> if the ARM machine does not have the resources to be able to bootstrap the
> compiler by itself.
>

And for what it's worth, the reason it's called "Canadian" is because at
the time of it's naming, Canada had 3 political parties.

http://en.wikipedia.org/wiki/Cross_compiler#Canadian_Cross


> Hope that made some things clear.
>
> Michael
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