Re: kernel-image-2.6.7

From: Geert Uytterhoeven
Date: Wed Aug 25 2004 - 16:20:39 EST


[ Background: M68k 2.6.x kernels with CONFIG_MODULES=y have been crashing very
early for me since quite a while. The problem seems to be incorrect addresses
(and thus sizes) for various variables, causing data structure corruption ]

On Mon, 23 Aug 2004, Geert Uytterhoeven wrote:
> On Sun, 22 Aug 2004, Roman Zippel wrote:
> > Geert Uytterhoeven wrote:
> > > Easily explained by System.map:
> > > | 00194090 B amiga_model
> > > | 00194090 B m68k_memory
> > > | 00194094 B amiga_chipset
> > >
> > > So initializing amiga_model kills m68k_memory...

[ m68k_memory is supposed to be 32 bytes long, not 4 bytes ]

> > Anyway, I still can't reproduce this, but from the object files I've
> > seen, it seems the bss isn't correctly set. Could you please check the
> > various object files under arch/m68k/{kernel,amiga} for their bss size?
>
> At first sight, there seem to be more of them with a zero bss if
> CONFIG_MODULES=y. Will be investigated...

Indeed, in arch/m68k/kernel/setup.o .bss and .init.data become zero-sized,
while all other sections have the same size.

If I do `make V=1 arch/m68k/kernel/setup.o', I get:

| anakin$ make V=1 arch/m68k/kernel/setup.o
| make -C /home/geert/linux/testing/linux-m68k-2.6.9-rc1 O=/home/geert/linux/testing/linux-m68k-2.6.x-amiga-mod arch/m68k/kernel/setup.o
| make -C /home/geert/linux/testing/linux-m68k-2.6.x-amiga-mod \
| KBUILD_SRC=/home/geert/linux/testing/linux-m68k-2.6.9-rc1 KBUILD_VERBOSE=1 \
| KBUILD_CHECK= KBUILD_EXTMOD="" \
| -f /home/geert/linux/testing/linux-m68k-2.6.9-rc1/Makefile arch/m68k/kernel/setup.o
| make -f /home/geert/linux/testing/linux-m68k-2.6.9-rc1/scripts/Makefile.build obj=scripts/basic
| make -f /home/geert/linux/testing/linux-m68k-2.6.9-rc1/scripts/Makefile.build obj=scripts
| make -f /home/geert/linux/testing/linux-m68k-2.6.9-rc1/scripts/Makefile.build obj=scripts/genksyms
| make -f /home/geert/linux/testing/linux-m68k-2.6.9-rc1/scripts/Makefile.build obj=scripts/mod
| make -f /home/geert/linux/testing/linux-m68k-2.6.9-rc1/scripts/Makefile.build obj=arch/m68k/kernel arch/m68k/kernel/setup.o
| m68k-linux-gcc -Wp,-MD,arch/m68k/kernel/.setup.o.d -nostdinc -iwithprefix include -D__KERNEL__ -Iinclude -Iinclude2 -I/home/geert/linux/testing/linux-m68k-2.6.9-rc1/include -I/home/geert/linux/testing/linux-m68k-2.6.9-rc1/arch/m68k/kernel -Iarch/m68k/kernel -Wall -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -pipe -fno-strength-reduce -ffixed-a2 -m68040 -O2 -fomit-frame-pointer -DKBUILD_BASENAME=setup -DKBUILD_MODNAME=setup -c -o arch/m68k/kernel/.tmp_setup.o /home/geert/linux/testing/linux-m68k-2.6.9-rc1/arch/m68k/kernel/setup.c
| anakin$

Note that according to the last line, m68k-linux-gcc will store its output in
arch/m68k/kernel/.tmp_setup.o instead of arch/m68k/kernel/setup.o! But
afterwards there is no arch/m68k/kernel/.tmp_setup.o, only
arch/m68k/kernel/setup.o?

If I execute the m68k-linux-gcc command by hand, it does create
arch/m68k/kernel/.tmp_setup.o, and ... surprise! The sizes of the .bss and .init.data sections in that file are correct:

| anakin$ m68k-linux-objdump -h arch/m68k/kernel/.tmp_setup.o
|
| arch/m68k/kernel/.tmp_setup.o: file format elf32-m68k
|
| Sections:
| Idx Name Size VMA LMA File off Algn
| 0 .text 0000024a 00000000 00000000 00000034 2**2
| CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
| 1 .data 0000001a 00000000 00000000 00000280 2**2
| CONTENTS, ALLOC, LOAD, RELOC, DATA
| 2 .bss 00000188 00000000 00000000 0000029c 2**2
^^^^^^^^
| ALLOC
| 3 .note 00000014 00000000 00000000 0000029c 2**0
| CONTENTS, READONLY
| 4 .init.data 00000008 00000000 00000000 000002b0 2**1
^^^^^^^^
| CONTENTS, ALLOC, LOAD, DATA
| 5 __kcrctab 00000004 00000000 00000000 000002b8 2**1
| CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
| 6 __ksymtab_strings 0000000f 00000000 00000000 000002bc 2**0
| CONTENTS, ALLOC, LOAD, READONLY, DATA
| 7 __ksymtab 00000008 00000000 00000000 000002cc 2**1
| CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
| 8 .rodata 00000256 00000000 00000000 000002d4 2**0
| CONTENTS, ALLOC, LOAD, READONLY, DATA
| 9 .init.text 00000396 00000000 00000000 0000052a 2**1
| CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
| 10 .comment 0000002f 00000000 00000000 000008c0 2**0
| CONTENTS, READONLY
| anakin$

while .bss and .init.data are of size zero in arch/m68k/kernel/setup.o:

| anakin$ m68k-linux-objdump -h arch/m68k/kernel/setup.o
|
| arch/m68k/kernel/setup.o: file format elf32-m68k
|
| Sections:
| Idx Name Size VMA LMA File off Algn
| 0 .text 0000024a 00000000 00000000 00000034 2**2
| CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
| 1 __kcrctab 00000004 00000000 00000000 0000027e 2**1
| CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
| 2 __ksymtab_strings 0000000f 00000000 00000000 00000282 2**0
| CONTENTS, ALLOC, LOAD, READONLY, DATA
| 3 __ksymtab 00000008 00000000 00000000 00000292 2**1
| CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
| 4 .rodata 00000256 00000000 00000000 0000029a 2**0
| CONTENTS, ALLOC, LOAD, READONLY, DATA
| 5 .init.text 00000396 00000000 00000000 000004f0 2**1
| CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
| 6 .data 0000001a 00000000 00000000 00000888 2**2
| CONTENTS, ALLOC, LOAD, RELOC, DATA
| 7 .bss 00000000 00000000 00000000 000008a4 2**2
^^^^^^^^
| ALLOC
| 8 .init.data 00000000 00000000 00000000 000008a4 2**1
^^^^^^^^
| CONTENTS, ALLOC, LOAD, DATA
| 9 .note 00000014 00000000 00000000 000008a4 2**0
| CONTENTS, READONLY
| 10 .comment 0000002f 00000000 00000000 000008b8 2**0
| CONTENTS, READONLY
| anakin$

Now the remaining questions are:
1. Why does kbuild create arch/m68k/kernel/.tmp_setup.o?
2. How does kbuild create setup.o from .tmp_setup.o, destroying .bss and
.init.data?
3. Why doesn't the above step show up with `make V=1'?

[ digging into scripts/Makefile.build ]

Aha, kbuild does this only if CONFIG_MODVERSIONS=y.

So it goes wrong during this step:

| m68k-linux-ld -r -o x.o arch/m68k/kernel/.tmp_setup.o -T \
| arch/m68k/kernel/.tmp_setup.ver

| anakin$ cat arch/m68k/kernel/.tmp_setup.ver
| __crc_mach_heartbeat = 0x39638af7 ;
| anakin$

Does the above look like a valid linker file? `mach_heartbeat' is indeed the
only exported symbol in arch/m68k/kernel/setup.c.

[ disabling CONFIG_MODVERSIONS ]

And now .bss and .initdata are OK as well... Let's see whether the resulting
kernel works...

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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