[uml-devel] Re: Supporting building on x86-64 host as 32-bit UML

[Gerd Knorr <kraxel@bytesex.org>]

> 1) how the user must choose what he wants (SUBARCH=i386 can be useful,
> maybe a Kconfig option would be nice - we need to choose the default
> depending on the host arch).

That one is easy -- just use "linux32 make ...".  That will switch the
personality and "uname" will return "i686" instead of "x86_64" then ;)

> 2) using the proper options for the tools (addressed partially by the
> patch below)

Probably still needed.  Maybe not any more with gcc4, I remember there
was some discussion among the gcc folks to make gcc default to -m64 /
-m32 depending on the current personalily.  In that case the linux32
thingy mentioned above should catch that one as well.  Not sure that
actually happened.

> 3) using the proper headers (asm-i386 instead of asm-x86_64)... Fedora

linux32 should fix that one as well.

> +AFLAGS		+= -m32
> +CFLAGS		+= -m32

I think that can also be fixed on the make command line, with a small
wrapper script -- named make32 for example -- doing something like this:

  #!/bin/sh
  exec linux32 make CC="gcc -m32" AS="as -m32" ... "$@"

Last time I tried I ran into the problem that the glibc headers of the
x86_64 biarch compiler slightly different from the ones on a real i386
machine, thus some #ifdefs in uml userspace code didn't work as expected
and broke the build.

> +HOSTCFLAGS	+= -m32
> +HOSTLDFLAGS	+= -m32

Not needed I think.  Thats used for kconfig and other stuff which runs
on the _host_ machine (for cross compiles), thus it doesn't hurt if it
is 64 bit.

  Gerd

-- 
#define printk(args...) fprintf(stderr, ## args)


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