linux-kernel - Re: [RFC] Limiting linker scope

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Date:	Fri, 20 Nov 2015 00:34:20 +0100
From:	Richard Weinberger <richard@....at>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:	Linux-Arch <linux-arch@...r.kernel.org>, octavian.purdila@...el.com
Subject: Re: [RFC] Limiting linker scope

Am 19.11.2015 um 23:50 schrieb Richard Weinberger:
> Hi!
> 
> UML recently had an interesting bug[1] where the host side of UML
> tried to call sigsuspend() but as the kernel itself offers a function
> with the same name it called sigsuspend() on
> the UML kernel side and funny things happened.
> 
> The root cause of the problem is that the UML links userspace
> code like glibc, libpcap, etc. to the kernel image and symbols can
> clash. Especially if one side is a shared library it will not noticed
> at compile time.
> 
> As this is not the first bug of this kind I'm facing on UML I've
> started to think how to deal with that.
> 
> Is it somehow possible to limit the linker scope?
> Such that we can force LD no not blindly link every symbols of
> vmlinux into another object? Maybe using a white list?
> I have do admit I've never used LD scripts nor GNU export maps,
> maybe they can help. Currently I'm reading their docs and hope
> to find a way to implement my idea.
> 
> The problem is also not specific to UML, the emerging Linux Kernel
> Library will suffer from the same issue.

I take this back. LKL continues to impress me.
It creates a new kernel object using objcopy -G and marks only some
symbols as global. This approach could work for UML too.

Thanks,
//richard
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