linux-kernel - Re: [musl] musl-libc/MIPS: detached thread exit broken since kernel commit 46e12c07b

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Message-ID: <20150619143539.GU1173@brightrain.aerifal.cx>
Date:	Fri, 19 Jun 2015 10:35:39 -0400
From:	Rich Felker <dalias@...c.org>
To:	Ralf Baechle <ralf@...ux-mips.org>
Cc:	Matthias Schiffer <mschiffer@...verse-factory.net>,
	musl@...ts.openwall.com, linux-mips@...ux-mips.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [musl] musl-libc/MIPS: detached thread exit broken since kernel
 commit 46e12c07b

On Fri, Jun 19, 2015 at 12:06:26PM +0200, Ralf Baechle wrote:
> On Thu, Jun 18, 2015 at 10:50:32PM -0400, Rich Felker wrote:
> 
> > This is kernel ABI breakage that should be fixed -- people running old
> > kernel versions with old musl binaries might suffer a regression when
> > upgrading, and perhaps more importantly the failure mode is just
> > really bad. But I think we can also work around it on the userspace
> > side in musl by pointing the stack pointer at some rodata (or even at
> > pc, e.g. copying $25 to $sp) before making the syscall.
> 
> Just to be on the safe side, make sure it is something that's readable.  Core
> might me mapped execute-only, that is not readable and that is a feature
> which the affected kernels do support on suitable hardware.

How would that happen? Do you have ELF files with 3 PT_LOAD segments?
Normally there are two and their permissions are r-x and rw-.

Rich
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