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SubjectKernel Cross Compiling [update]

Hi Folks!

Here is an update to the Kernel Cross Compiling thread
I started ten days ago ...

1) CROSS COMPILER / TOOLCHAIN

there are different solutions for the toolchain issue:

- Dan Kegel's Crosstool [1]
- PTXdist [2]
- my simplified approach [3]

in one mail [Ref-A], Jim Wilson mentioned that using the
'inhibit_libc' trick will break the gcc in a subtly way,
so I decided to verify the fitness of the compiled gcc.

because 'normal' checks won't work without the glibc and
the includes, I decided to take the following approach:

- build gcc 3.3.2 with Dan's crosstool, and with my
simplified approach.

- select all tests from the test suite which contain
tests relevant for the kernel (no floats, no (g)libc
includes)

- compile each C source into Assembler code (gcc -O2 -S)
with both compilers (crosstool gcc version and mine)

- compare the resulting Assembler code and check for
differences

the GCC testsuite contains 2854 files in the relevant
subdirs consistency.vlad, gcc.c-torture, gcc.dg, and
gcc.misc-tests.

after removing the non relevant tests (file matching
egrep '#include|float|double') 1799 C files remain.
the result of the tests and comparison[4] shows that
both compilers produce the same code, except for one
little difference[5], which I'm unable to explain ...

my conclusion so far is that my approach should be
sufficient for Kernel Cross Compiling.


2) KERNEL CROSS COMPILING

linux-2.6.3-rc3 linux-2.6.3
config build config build

alpha/alpha: OK OK OK OK
arm/arm: FAILED FAILED FAILED FAILED
cris/cris: FAILED FAILED FAILED FAILED
hppa/parisc: OK FAILED OK FAILED
hppa64/parisc: OK FAILED OK FAILED
i386/i386: OK OK OK OK
ia64/ia64: OK OK OK OK
m68k/m68k: OK FAILED OK FAILED
mips/mips: OK FAILED OK FAILED
mips64/mips: OK FAILED OK FAILED
ppc/ppc: OK FAILED OK FAILED
ppc64/ppc64: OK OK OK OK
s390/s390: OK FAILED OK FAILED
sh/sh: OK FAILED OK FAILED
sh64/sh: OK FAILED OK FAILED
sparc/sparc: OK FAILED OK FAILED
sparc64/sparc64: OK OK OK OK
v850/v850: FAILED FAILED FAILED FAILED
x86_64/x86_64: OK OK OK OK


interesting is that some architectures (arm, chris, v850)
do not even have an appropriate default config, where
others seem to require different? binutils (sh and sh64)
but most other issues seem to be inconsistent configs or
broken headers/code (details [6])...

mips/mips64 seems to break because of an cpu= option
which was depreciated in gcc some time ago, so they might
build again if those changes are merged back into mainline

hppa/hppa64 seems to require heavy patches to make them
compile, which might be too intrusive to get into mainline
very soon.

linux-2.4.25
config dep kernel modules

alpha/alpha: OK OK OK OK
arm/arm: OK OK FAILED FAILED
cris/cris: OK FAILED FAILED FAILED
hppa/parisc: OK OK FAILED FAILED
hppa64/parisc: OK OK FAILED FAILED
i386/i386: OK OK OK OK
ia64/ia64: OK OK FAILED FAILED
m68k/m68k: OK OK OK OK
mips/mips: OK OK FAILED FAILED
mips64/mips64: OK OK FAILED FAILED
ppc/ppc: OK OK OK OK
ppc64/ppc64: OK FAILED FAILED OK
s390/s390: OK OK OK OK
sh/sh: OK OK FAILED FAILED
sh64/sh64: OK OK FAILED FAILED
sparc/sparc: OK OK FAILED OK
sparc64/sparc64: OK OK OK OK
v850/v850: FAILED FAILED FAILED FAILED
x86_64/x86_64: OK OK OK OK


the logs[7] for the 2.4.25 kernel build suggest similar
reasons for similar architectures (compared to 2.6.3)

3) CONCLUSIONS

it seems that the fast/easy way to build a cross gcc
compiler (at least on x86 ;) is sufficient for kernel
cross compile tests.

6/7 out of 19 'supported' architectures are currently
building with the kernel default configuration, when
cross compiled in an x86 host (about a third).


best,
Herbert



[1] http://kegel.com/crosstool
[2] http://www.pengutronix.de/software/ptxdist_en.html
[3] http://vserver.13thfloor.at/Stuff/Cross/howto.info
[4] http://vserver.13thfloor.at/Stuff/Cross/Comparison
[5] http://vserver.13thfloor.at/Stuff/Cross/Comparison/TEST-alpha.diff
[6] http://vserver.13thfloor.at/Stuff/Cross/LOGS-2.6.3
[7] http://vserver.13thfloor.at/Stuff/Cross/LOGS-2.4.25

[Ref-A]

On Mon, Feb 16, 2004 at 02:50:41PM -0800, Jim Wilson wrote:
> I recommend Dan Kegel's page for anyone trying to build a cross compiler
> to linux. See
> http://kegel.com/crosstool
> This isn't very hard to follow, and it gives you a properly configured
> and built gcc/glibc for the target.
>
> I don't recommend the inhibit_libc trick for building linux crosses.
> It may work well enough for kernel builds, but it will give you a subtly
> broken gcc, and that may lead to confusion later.

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