[llvm-dev] whole linux kernel bitcode

[Kai Wang via llvm-dev]

>
>  First, you can use llvm-link to link the bitcode files together.  This
> will require some manual changes to the Linux Makefiles.  Once you get a
> single bitcode file, you can run your analysis pass via opt.  This is the
> approach that I used for the original SVA system for Linux 2.4.22 back
> before we had libLTO.



When I generate bitcode files,  I pass -emit-llvm flag to compiler command
line ( clang -emit-llvm "a long list of parms"  *.c ) so that it generates
.bc files during compilation.  Since -emit-llvm doesn't change the name of
file output, I rename *.o file to *.bc file.
Then I run compiler  again ( clang "a long list of parms" *.c ) to generate
*.o file otherwise Kbuild would break. So basically I create *.bc files
next to all the  *.o files (where possible)

How should I modify Makefiles to link all the bitcode files together? Could
you share with me some experience?
My guess is to use llvm-link to link bitcode files along with every ld
command line?
For example,
For " ld -r -o init/mounts.o init/do_mounts.o init/do_mounts_initrd.o
init/do_mounts_md.o; "
I'll have something like " llvm-link -o init/mounts.bc init/do_mounts.bc
init/do_mounts_initrd.bc init/do_mounts_md.bc; " ?

Thank you!

Kai

On Wed, Jan 6, 2016 at 7:53 AM, John Criswell <jtcriswel at gmail.com> wrote:

> On 1/6/16 9:41 AM, Kai Wang via llvm-dev wrote:
>
>
> Hi all,
>
> I'm trying to generate whole program bitcode files for linux kernel and do interprocedural
> analysis on kernel.
>
> I use llvmlinux to compile kernel with clang and  generate a bunch of
> bitcode files successfully.
> I need to link all these bitcode files together into a single bitcode
> file, so that I can run whole program analysis.
>
> Should I use libLTO to link all these bitcode files together? I guess I
> have to modify the linux kernel's build scripts and Makefiles?
> I'm kind of confused. Any suggestions?
>
>
> There are two ways to do it.
>
> First, you can use llvm-link to link the bitcode files together.  This
> will require some manual changes to the Linux Makefiles.  Once you get a
> single bitcode file, you can run your analysis pass via opt.  This is the
> approach that I used for the original SVA system for Linux 2.4.22 back
> before we had libLTO.
>
> Second, you could add your pass to libLTO and change the Linux Makefiles
> to use the -flto option.  This method should require fewer Makefile changes
> but will require you to build and install your own libLTO library.
>
> Regards,
>
> John Criswell
>
>
>
> Thank you
>
> Regards,
> Kai
>
>
>
> _______________________________________________
> LLVM Developers mailing listllvm-dev at lists.llvm.orghttp://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>
> --
> John Criswell
> Assistant Professor
> Department of Computer Science, University of Rochesterhttp://www.cs.rochester.edu/u/criswell
>
>


-- 
Regards,
Kai
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