Re: [PATCH] remove target_os

[Christian Franke]

Javier Martín wrote:
> El mar, 27-01-2009 a las 18:21 +0100, Christian Franke escribió:
>   
> > Javier Martín wrote:
> >     
> > > > Unfortunately, gcc has no '-fno_os' option to specify the bare CPU as 
> > > > target.
> > > >     
> > > >         
> > > Might -ffreestanding be what you are looking for?
> > >
> > >   
> > >       
> > The option '-ffreestanding' is the same as '-fno-hosted'.
> >
> > According to gcc (4.3.1) source, '-fno-hosted' clears variable 
> > 'flag_hosted' and sets '-fno-builtin'. The latter is already set within 
> > GRUB build.
> >
> > A cleared 'flag_hosted' apparently has only 2 effects:
> > - disable the special handling of 'main()'.
> > - #define __STDC_HOSTED__ to 0 instead of 1
> >
> > There is no effect on the target_os dependent parts of the gcc code 
> > generation. For example, on i386, __enable_execute_stack() calls are 
> > generated for target_os netbsd, openbsd and cygwin, but not for linux. 
> > The emit call is hard-coded in 
> > gcc/configs/i386/i386.c:x86_initialize_trampoline().
> >     
>
> In that case, we are dealing with a GCC bug. We might want to require
> the user to create a bare "no-OS" cross compiler. 
>
>   

Is building a bare 'no-OS' compiler supported by the upstream GCC sources?
Probably a too strict prerequisite for building GRUB.


> > > > >  AC_MSG_CHECKING([for command to convert module to ELF format])
> > > > > -case "${host_os}:${target_os}" in
> > > > > -  cygwin:cygwin) TARGET_OBJ2ELF='grub-pe2elf' ;;
> > > > > +case "${host_os}" in
> > > > > +  cygwin) TARGET_OBJ2ELF='grub-pe2elf' ;;
> > > > >    *) ;;
> > > > >  esac
> > > > >   
> > > > >       
> > > > >           
> > > > This won't work for a Linux cross compiler hosted on Cygwin. It would 
> > > > emit ELF format and does not need pe2elf.
> > > >     
> > > >         
> > > A, say, AMD64 Linux cross compiler hosted on x86 Cygwin would have
> > > $build=i686-pc-cygwin and $host=amd64-linux-gnu. Thus, no conflict ought
> > > to arise even with cross compilation enabled.
> > >
> > >   
> > >       
> > But the opposite won't work: $host=i686-pc-cygwin would enable 
> > grub-pe2elf, even if this gcc emits ELF for a linux target.
> >     
>
> "The opposite" of a the described situation would be a Linux AMD64
> machine cross compiling for a Cygwin x86 machine, that is
> $build=amd64-linux-gnu and $host=i686-pc-cygwin. In that case,
> i686-pc-cygwin-gcc would generate PE executables, and thus grub-pe2elf
> _is_ required indeed.
>   

Yes - I was wrong, sorry.


Robert: Patch is IMO GTG.

Christian