Re: [uClinux-dev] Re: [linuxsh-dev] init problems on MMU-less SH-4

[David M. <da...@sn...>]

Jivin Paul Mundt lays it down ...
> On Sun, 2003-01-05 at 20:34, David McCullough wrote:
> > I suspect that you are still running ELF programs.  When you turn off the
> > MMU support in the kernel,  the rules for applications change a little.
> > They cannot be paged in for example, and they have to be loaded (and
> > relocated) at run time.  Normal elf programs are loaded at a fixed
> > addresses and this cannot work without an MMU.
> > 
> > The uClinux guys use a program called elf2flt (ELF to flat) to make flat
> > binaries that can be run without an MMU.  You can find it at:
>
> Okay, one issue with elf2flt. I've built a static busybox linked against
> uClibc (which was built w/o HAS_MMU set), also using the sh-uclibc-
> toolchain (which is also built w/o HAS_MMU). Now, this busybox itself
> doesn't have any relocations in it, though it's still an ELF.


Ok,  I guess it's a possibility that on SH you can generate an executable
that doesn't need relocations,  but I would be suspicious,  especially if
it isn't built with PIC.  It sounds like elf2flt is not being used
correctly as all the SH code I have seen generated would need relocations
to run on a non-MMU system.


> elf2flt currently bails and refuses to write the flt hdr/file if it sees
> that the ELF doesn't have anything needing relocation. This happens
> around line 900 of elf2flt.c from current HEAD by way of the
> bfd_get_file_flags() HAS_RELOC check. If I comment this out, the flt
> file is generated properly.
> 
> This brings up the question, if I have an ELF that was built with PIC
> turned off, can binfmt_elf deal with it? or does it still have to pass
> through binfmt_flat?


binfmt_elf will deal with it,  but the program will not run.  You would
have to link every application at a different address and then make sure
that you never ran more than one instance of each.  Even then I doubt it
would work.  You will need to use flat executables to get it going.


> > 	http://cvs.uclinux.org/cgi-bin/cvsweb/elf2flt/
> > 
> > I don't believe there is SH support in it at the moment,  but it isn't a
> > huge amount of work. Generally only a few relocation types need to be
> > handled,
> 
> Currently I have R_SH_DIR32, R_SH_REL32, R_SH_GOT32 and R_SH_GOTPC
> supported. I'll submit patches for this once the above mess is worked
> out.

Sounds good.

By the way,  I subscribed to linuxsh-dev a month or so ago and haven't seen
any traffic.  It is working or am I missing something ?

Cheers,
Davidm

-- 
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