Re: [PATCH] remove target_os

[Javier Martín]

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. These thingies are
most likely only known to OS developers, but you can build a perfectly
good "i686-pc-elf" GCC (only with no libc, of course). This might be the
Right Way (TM) of building boot code, instead of the current way of
using the OS-targetter compiler and trying to tell it not to do what it
was built to do.

> 
> Other workarounds are needed to support building GRUB with code 
> generators tailored for various target_os.
> 
> 
> >>
> >>>  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.

> 
> Christian
> 
> 
> 
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