[uml-devel] Re: 2.4.32-bs2

[Blaisorblade <blaisorblade@yahoo.it>]

On Thursday 08 December 2005 03:10, Antoine Martin wrote:
> All,
>
> Talking about tty logging and fake ide reminded of the current state of
> UML on 2.4 kernels:
> http://uml.nagafix.co.uk/uml-2.4.32-bs2.patch.bz2
> Is Blaisorblade's 2.4.28-bs2 patch tweaked to apply cleanly on 2.4.32.

There should be (I think) just offsets, not even fuzzes, so there should be no 
problem.

> Plus another tweak to avoid duplicated symbols when linking with newer
> libc.a, the patch is based on this one:
> http://seclists.org/lists/linux-kernel/2004/Nov/1048.html
> But I'm not sure I did it right, so please check it (bottom of this
> email is the modified Makefile)

Seems correct for what I can see. Ah, no, there's a 2.4 / 2.6 conversion 
problem, see below.

> /usr/lib/libc.a: could not read symbols: Bad value

I'd like to see the exact cmd line producing this. Possibly seeing also gcc -v 
output with that cmd line would help.

(After seeing if there's anything strange with the file itself, but I think 
you can compile on the same box some 

> Any idea why that is? It happens when I use:
> i686-pc-linux-gnu-3.4.4-vanilla
> but not with:
> i686-pc-linux-gnu-3.3.6-vanilla 

The first thing I'd do there (since this is the fscking 2.4, not the shining 
2.6) is doing a make mrproper ARCH=um between the two compiles... 2.4 kbuild 
was so erratic that even recently I was bitten from it, too... I started 
writing a patch (missing export_symbol, I thought) to discover that a) the 
code seemed right and b) the code _was_ right.

Afterwards I'd be curious if some strange Gentoo thing is mixing 
runtime .so/.a libraries of the two compilers (I've had this happening for 
c++, and programs crashing after linking with both gcc 3.3 and gcc 3.4 stdc++ 
libraries - fix_libtool_files.sh on Gentoo was my friend in the end). Note 
that you need to be especially lucky to trigger this - of the whole KDE 
3.4.3, most was linked this way, but only "juk" suffered.

No idea, I'll look at it a bit (maybe), but it's very strange. Note that I 
recall compiling that with GCC 3.4.x (.3?) - I wanted to support 3.4 when 
releasing -bs2.

> Problem is that the resulting kernel cannot be executed!
> $ kernel32-2.4.32-bs2: cannot execute binary file

file vmlinux-* and/or dmesg|tail would maybe help on what was going on.

> The other problem with this patch is that I can't get it to compile with
> SUBARCH=i386 on amd64.
> (even though -bs2 contains a SUBARCH fix - maybe I didn't merge it
> properly?)

Hmm, I never compiled 2.4 kernels on x86_64 machines. Probably I backported 
just an earlier attempt - in fact I thought I'd done it on 2.6, but until I 
started testing it, it didn't work.

For that, I'm sorry but you need a chroot - just too much work and I've not 
the time to work on this.

> Any ideas?

> Antoine

> Here is the modified Makefile

Next time send a patch (even cut 'n' paste, but a patch).

> $ cat linux-2.4.32-bs2/arch/um/kernel/tt/Makefile
> #
> # Copyright (C) 2002 - 2003 Jeff Dike (jdike@addtoit.com)
> # Licensed under the GPL
> #
>
> O_TARGET = tt.o
>
> obj-y = exec_kern.o exec_user.o gdb.o ksyms.o mem.o mem_user.o
> process_kern.o \
>         syscall_kern.o syscall_user.o time.o tlb.o tracer.o trap_user.o
> \
>         uaccess.o uaccess_user.o

> extra-y := unmap_fin.o
> clean-files := unmap_tmp.o

Get rid of these lines, they didn't exist. Extra-y must be expressed, but ok, 
it's already coded (see below). (clean-files is for make clean).

> obj-$(CONFIG_PT_PROXY) += gdb_kern.o
>
> subdir-y = sys-$(SUBARCH)
> subdir-$(CONFIG_PT_PROXY) += ptproxy
>
> obj-y += $(join $(subdir-y),$(subdir-y:%=/%.o))
>
> export-objs = ksyms.o
>
> USER_OBJS = $(filter %_user.o,$(obj-y)) gdb.o time.o tracer.o
>
> UNMAP_CFLAGS := $(patsubst -pg -DPROFILING,,$(USER_CFLAGS))
> UNMAP_CFLAGS := $(patsubst -fprofile-arcs -ftest-coverage,,
> $(UNMAP_CFLAGS))
>
> include $(TOPDIR)/Rules.make
>
> $(USER_OBJS) : %.o: %.c
>         $(CC) $(CFLAGS_$@) $(USER_CFLAGS) -c -o $@ $<

USER_CFLAGS and CFLAGS_$@ are in the wrong order, the latter must be able to 
override the former. Not that it should be a problem here... (and it's even 
in the original, so don't worry).

> $(O_TARGET) : unmap_fin.o

The above is the (approximate) equivalent of extra-y setting.

> unmap.o: unmap.c
>         $(CC) $(UNMAP_CFLAGS) -c -o $@ $<
>
> unmap_fin.o : unmap.o
>         ld -r -o unmap_tmp.o unmap.o -lc -L/usr/lib
>         objcopy unmap_tmp.o unmap_fin.o -G switcheroo

Yep, these are correct.

> clean :

-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

	

	
		
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