[LLVMdev] compile linux kernel

[Ashish Bijlani]

Thanks for the help. I've a couple of questions though:

How does LLVM deal with inline assembly?

I'm trying to compile kernel and I get this error probably because
LLVM is not able to handle inline assembly. I'm using LLVM-2.3

code snippet from "arch/x86_64/kernel/asm-offsets.c"
....

#define DEFINE(sym, val) \
        asm volatile("\n->" #sym " %0 " #val : : "i" (val))
....

    DEFINE(__NR_syscall_max, sizeof(syscalls) - 1);
    return 0;

# make CROSS_COMPILE=llvm- V=1

  llvm-gcc -Wp,-MD,arch/x86_64/kernel/.syscall.o.d  -nostdinc -isystem
/home/ashish/llvm/llvm-gcc4.2-2.3.source/obj/../install/lib/gcc/x86_64-unknown-linux-gnu/4.2.1/include
-D__KERNEL__ -Iinclude  -include include/linux/autoconf.h -emit-llvm
-Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing
-fno-common -Werror-implicit-function-declaration -O2  -mtune=generic
-m64 -mno-red-zone -mcmodel=kernel -pipe -Wno-sign-compare
-fno-asynchronous-unwind-tables -funit-at-a-time -mno-sse -mno-mmx
-mno-sse2 -mno-3dnow -maccumulate-outgoing-args
-fomit-frame-pointer -g  -fno-stack-protector
-Wdeclaration-after-statement -Wno-pointer-sign
-D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(syscall)"
-D"KBUILD_MODNAME=KBUILD_STR(syscall)" -c -o
arch/x86_64/kernel/.tmp_syscall.o arch/x86_64/kernel/syscall.c
arch/x86_64/kernel/syscall.c:22: error: '__NR_syscall_max' undeclared
here (not in a function)
arch/x86_64/kernel/syscall.c:24: error: array index in initializer not
of integer type
arch/x86_64/kernel/syscall.c:24: error: (near initialization for
'sys_call_table')
In file included from arch/x86_64/kernel/syscall.c:25:
include/asm-x86_64/unistd.h:16: error: array index in non-array initializer
include/asm-x86_64/unistd.h:16: error: (near initialization for
'sys_call_table')
include/asm-x86_64/unistd.h:18: error: array index in non-array initializer

Note that I use "-emit-llvm" option with llvm-gcc. Is this correct of
am I missing something?
How can I fix this error?

Thanks,
Ashish

On Sat, Sep 27, 2008 at 7:03 PM, Andrew Lenharth <andrewl at lenharth.org> wrote:
> On Fri, Sep 26, 2008 at 9:19 PM, Ashish Bijlani
> <ashish.bijlani at gmail.com> wrote:
>> Hi,
>>
>> I'm trying to compile linux-2.6.23.16 with llvm-2.3. Is it at all
>> possible?
>
> Yes, but it requires significant hacking, and the result for 2.6 is a
> mostly bitcode kernel with a few userspace shared libraries linked in
> as objcode (yes, the kernel builds .so files and includes them in the
> binary).  There are a few changes here and there you can make to the
> kernel code to produce significantly nicer bitcodes too (e.g. rather
> than having module level asm  that makes symbols weak, you can just
> have gcc do it).
>
> The modification to the make system is not difficult, but it requires
> some work and an understanding of the kernel build system.
>
> Andrew
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