linux-kernel - Re: linux object file containing all kernel symbols and suitable for userspace linking?

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Date:	Mon, 29 Sep 2008 02:18:00 -0400
From:	"Daniel Rosenthal" <danielrosenthal@....org>
To:	"Jeff Dike" <jdike@...toit.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: linux object file containing all kernel symbols and suitable for userspace linking?

> These are provided by the linker script.

Ok, I took a look at both vmlinux_32.lds.S and uml.lds.S (I'm assuming
these are the linker scripts).  I also took a look at vmlinux.  I
didn't realize at first that vmlinux actually has some symbols in it.
I linked vmlinux to my programs using gcc and it compiled, but I got a
segmentation fault when I ran it.  What is the appropriate binary
format to use to output the kernel binary so it won't segfault in
userspace?  Ideally, I would like to add another target, say
vmlinux-user, that would output the kernel with all the same symbols
that vmlinux contains, but with a binary format suitable for userspace
linkage.  It looks from uml.lds.S that you don't use the default ELF
output format for UML.  Why is this?

I guess I probably need to write another architecture specific *.lds.S
file called something like vmlinux-user.lds.S and add a few lines to
the Makefile in the root directory to achieve what I am trying to do,
but I would like to find as general a solution as I can so that maybe
other architectures and other people can use the same solution for
doing kernel code unit tests without replicating a lot of code.

By the way, I noticed that you only have a single uml.lds.S file, and
consequently UML probably either only works on x86 (and x86-64), or
uses the same binary layout on all platforms.  I couldn't find
anywhere explicitly where you say UML only runs on x86, but just to
clarify, UML is x86 specific, right?

Daniel

> Work email - jdike at linux dot intel dot com

Sorry, I misread the {addtoit,linux.intel} as {addtoit,linux,intel} in
arch/um/Makefile.
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