Re: [PATCH] kernel/linux: change arch tuple to use -uclinux for uclinux toolchains

[Mike Frysinger <vapier@gentoo.org>]

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On Tuesday 25 September 2012 14:18:38 Esben Haabendal wrote:
> Mike Frysinger <vapier@gentoo.org> writes:
> > On Tuesday 25 September 2012 12:41:42 Yann E. MORIN wrote:
> >> Basically, 'bfin-elf' is for bare-metal, 'bfin-uclinux' if for
> >> flat-binaries with no shared libs, and 'bfin-linux' for FDPIC-ELF that
> >> allows shared libs.
> > 
> > correct, the current convention is that "-uclinux" is for FLAT
> > targets.
> 
> Ok, but where does this convention come from.  Or rather, who follows
> this convention?
> 
> It does not generally seem to be the convention used in GCC, at least
> not for all archs.
> 
> If linux-gnu is linux with glibc, linux-uclibc is uClinux/FDPIC-ELF with
> uClibc, and uclinux-uclibc is uClinux/FLAT with uClibc.

uClibc supports multiple file formats (including FDPIC-ELF and FLAT).  if you 
see a toolchain end in "-uclinux" or "-uclibc*", you're pretty much guaranteed 
to be using uClibc.

further, pretty much every target i've seen so far that ends in -uclinux was 
targeting the FLAT file format.  for Blackfin targets, we wanted a new tuple 
when using FDPIC-ELF, so we went with linux-uclibc rather than uclinux.  after 
all, when you're running Linux with the ELF format, the fact that you lack a 
MMU is largely transparent to userland (ignoring lack of fork).

> What arch tuple should then be used for linux with uClibc?  I don't see the
> benefit of not being able to tell it apart from uClinux/FDPIC-ELF with
> uClibc.

i don't understand the question.  "uclinux" means you're running Linux with 
uClibc, as does "linux-uclibc".

> --------
> m68k-*-uclinuxoldabi*)          # Motorola m68k/ColdFire running uClinux
>                                 # with uClibc, using the original
>                                 # m68k-elf-based ABI
>         default_m68k_cpu=68020
>         default_cf_cpu=5206
>         tm_file="${tm_file} m68k/m68k-none.h m68k/m68kelf.h dbxelf.h
> elfos.h m68k/uclinux-oldabi.h glibc-stdint.h" tm_defines="${tm_defines}
> MOTOROLA=1"
>         tmake_file="m68k/t-floatlib m68k/t-uclinux"
>         ;;
> m68k-*-uclinux*)                # Motorola m68k/ColdFire running uClinux
>                                 # with uClibc, using the new
> GNU/Linux-style # ABI.
>         default_m68k_cpu=68020
>         default_cf_cpu=5206
>         tm_file="${tm_file} dbxelf.h elfos.h svr4.h linux.h glibc-stdint.h
> flat.h m68k/linux.h m68k/uclinux.h ./sysroot-suffix.h"
> tm_defines="${tm_defines} MOTOROLA=1 UCLIBC_DEFAULT=1"
>         extra_options="${extra_options} linux.opt"
>         tmake_file="m68k/t-floatlib m68k/t-uclinux m68k/t-mlibs"
>         ;;
> m68k-*-linux*)          # Motorola m68k's running GNU/Linux
>                                 # with ELF format using glibc 2
>                                 # aka the GNU/Linux C library 6.
>         default_m68k_cpu=68020
>         default_cf_cpu=5475
>         with_arch=${with_arch:-m68k}
>         tm_file="${tm_file} dbxelf.h elfos.h svr4.h linux.h glibc-stdint.h
> m68k/linux.h ./sysroot-suffix.h" extra_options="${extra_options}
> m68k/ieee.opt"
>         tm_defines="${tm_defines} MOTOROLA=1"
>         tmake_file="${tmake_file} m68k/t-floatlib m68k/t-linux
> m68k/t-mlibs" # if not configured with --enable-sjlj-exceptions, bump the
> # libgcc version number
>         if test x$sjlj != x1; then
>             tmake_file="$tmake_file m68k/t-slibgcc-elf-ver"
>         fi
>         ;;
> --------
> 
> I guess that mean that at least for m68k, the convention you mention is
> not shared with GCC.

m68k doesn't support FDPIC-ELF.  i don't know what you're trying to show.

> When building an m68k cross gcc, using *-*-linux-* will filter out any
> target devices that does not have the FL_MMU flag set (in
> gcc/config/m68k/m68k-devices.def).  When building with *-*-uclinux-*,
> only those devices without FL_MMU flag set, or with FL_UCLINUX flag set
> will be available.
> 
> As such, the convention does not work for m68k.
> 
> As for my current needs, this can be made conditional for m68k.
> 
> That said, I don't think the convention is the most sane one, as it
> would be best to have "linux-uclibc" mean the same thing independent of
> the cpu prefix, and also in line with the principle of least surprise,
> it would make sense to use "uclinux-*" for uclinux archs :-)

looks to me like gcc only uses the FL_{MMU,UCLINUX} flags to figure out whether 
to build FLAT shared libraries.  so if you want those things, use m68k-
uclinux.  if you don't want those things, then use whatever target you want.
-mike

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