Re: "building binutils for target" question

[Michael Zintakis <michael dot zintakis at googlemail dot com>]

> So the question is: do you need to run a compiler on your target?
> If the answer is 'no', then all you need is the cross-toolchain.
>   
In my case, fortunately (or unfortunately, depending if a newbie like me 
has to do it) the answer is 'yes' as the target machine would need to 
compile and run programs using gcc, so I have to prepare everything on 
the (powerful) x86_64 arch machine, build the image, deploy it to the 
target powerpc and then let that machine do its business.

> > OK, but, presumably, when I construct that final image glibc should also 
> > be there (in the final image), right? how do I "move it across"? Where 
> > is it located (for the target arch)?
> >     
>
> Basically, you would follow these steps:
> - build the cross-toolchain ( with crostool-NG, of course! ;-) )
>
> - build every packages, and install them in what we call a 'staging area':
>   ./configure --build=x86_64-blabla --host=powerpc-blabla --prefix=/ --options
>   make
>   make DESTDIR=/some/place/staging
>   (note: you may need to pass additional CFLAGS and LDFLAGS, such as:
>     CFLAGS="-I/some/place/staging/usr/include -I/some/place/staging/include"
>     LDFLAGS="-L/some/place/staging/lib -L/some/place/staging/usr/lib"
>   )
>   
In your last "make" statement presumably you meant "make 
DESTDIR=/some/place/staging install" right?

As for the CFLAGS/LDFLAGS includes that is a given, although I am 
thinking if I run with chroot to /some/place/staging and then execute 
make install then I won't be needing this, right? I might be wrong though!

>   Note: do NOT install in the sysroot! If you do so, then you won't be
>   able to reuse the toolchain, as it would be poluted with headers and
>   libraries from your programs. You really want to install in a staging
>   area!
>   
I know, I've read all of the doc files and I am also aware of the 
populate tool, but to me it seemed a bit of a chicken-and-egg scenario - 
you need to build the tools in the staging area in order to use this 
script, but in effect I can't build the tools if I do not have the core 
libraries...

> - the staging area will contain all that your packages have installed, but
>   is missing the 'system' libraries from the toolchain. So crosstool-NG
>   does provide a tool that can complete the staging for you. That tool is
>   called populate:
>     powerpc-blabla-populate -s /some/place/staging -d /some/place/rootfs
>   populate will scan all binaires (executable and shared libs) in staging,
>   find missing NEEDED libs and get them from the sysroot, and create a copy
>   of staging in rootfs, which will contain all libs required to run.
>   Note: if you are using glibc, be sure to add (some or all of )the NSS
>   libraries. You can do it with the '-l' options of populate. See:
>     docs/5 - Using the toolchain.txt
>     populate --help
>   
But as you pointed out below, if I just copy all of the toolchain's 
sysroot to my staging area I won't need any of this, right? Would that 
mean that I do not have to install the kernel headers for the target 
machine as well?

> - you then create an 'image' of rootfs that you transfer to the target
>   and boot on that. It all depends on your target what this image will be:
>   - file system image to burn on flash
>   - tarball to extract on SD or HDD, or to NFS mount
>   - kernel+initrd to boot from the network
>   - and so on...
>   
Yeah, precisely! That is exactly what my plan is!

> > > You do not need to copy or install them again. The cross-gcc and cross-ld
> > > will be able to find them (and the libs) automatically. This is the purpose
> > > of the sysroot.
> > >   
> > >       
> > What about my "cross-native" gcc and the binutils I am going to build? 
> > Would they be able to find them (or should I use the --with-headers 
> > option when running configure, would that be enough do you think)?
> >     
>
> You would need to build the native gcc using the already built sysroot. Just
> copy the sysroot of the cross-toolchain, and use that copy to configure gcc.
> You could start by creating your staging by entirely copying the sysroot
> as-is, and then configure gcc with --disable-sysroot and --with-build-sysroot
> that points to the staging.
>   
And also presumably using --with-headers as well, right?

> Of course, in this case, you would not need to run populate, as your staging
> will already have everything...
>   
True, but are there any drawback with using this approach (it is a given 
that I may copy something, which I won't be needing on the target machine)?


MZ

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