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Subjectbinutils woes
Hi guys,

On ARM, we appear to have somewhat of a problem with binutils. At
least the following binutils suffer from a problem whereby it is
possible to create programs which contain undefined symbols:

GNU assembler 2.13.90.0.18 20030206
GNU assembler 2.14 20030612
GNU assembler 2.14.90 20031229
GNU ld version 2.14.90.0.7 20031029 Debian GNU/Linux
Assembleur GNU 2.15.90.0.1 20040303

We discovered this back in April, and at the time we thought that
adding --no-undefined to the linker command line would ensure that
we caught this bug.

However, this appears not to be the case. I recently committed
this change:

http://linux.bkbits.net:8080/linux-2.5/cset@1.1769.3.12??nav=index.html|ChangeSet@-4d

and tested it - it appeared to build fine, and nothing untoward.
However, as you can see from this patch:

http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=1950/1

It appears that we are successfully build a kernel without the correct
value of SIZEOF_MACHINE_DESC - in fact, this constant appears to be
undefined in arch/arm/kernel/head.S. Upon checking the build logs
and object files here, I have been able to confirm that this is
exactly what has happened.

Here is an example of the build output around the affected files:

...
AS arch/arm/kernel/debug.o
LD arch/arm/kernel/built-in.o
AS arch/arm/kernel/head.o
CC arch/arm/kernel/init_task.o
...
CC arch/arm/lib/udivdi3.o
AR arch/arm/lib/lib.a
GEN .version
CHK include/linux/compile.h
UPD include/linux/compile.h
CC init/version.o
LD init/built-in.o
LD .tmp_vmlinux1
KSYM .tmp_kallsyms1.S
AS .tmp_kallsyms1.o
LD .tmp_vmlinux2
KSYM .tmp_kallsyms2.S
AS .tmp_kallsyms2.o
LD vmlinux
OBJCOPY arch/arm/boot/Image
Kernel: arch/arm/boot/Image is ready

As you can see - there is no indication of failure what so ever.
However, if we inspect the symbol information for vmlinux, we find:

[rmk@dyn-67 versatile]$ arm-linux-nm vmlinux | grep SIZEOF -2
c0008000 T _sinittext
c0060634 T si_swapinfo
U SIZEOF_MACHINE_DESC
c013cb7c T sk_alloc
c014cc34 T sk_attach_filter

and further investigation of the disassembly indicates that the
assembler subsituted a value of zero for this constant.

Since ld --no-undefined does not catch this error, and this error
affects a range of binutils versions from 2.13 through to 2.15, I
don't think we can ignore the problem.

I think the only way we can ensure kernel correctness is to add a
subsequent stage to kbuild such that whenever we generate a final
program, we grep the 'nm' output for undefined symbols.

Comments?

--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 PCMCIA - http://pcmcia.arm.linux.org.uk/
2.6 Serial core
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