Re: [PATCH] remove target_os

[Christian Franke <Christian.Franke@t-online.de>]

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().

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.

Christian