From: Rich Felker <dalias@aerifal.cx>
To: musl@lists.openwall.com
Subject: Re: tough choice on thread pointer initialization issue
Date: Sat, 25 Feb 2012 08:32:13 -0500 [thread overview]
Message-ID: <20120225133213.GG184@brightrain.aerifal.cx> (raw)
In-Reply-To: <20120225065613.GF184@brightrain.aerifal.cx>
On Sat, Feb 25, 2012 at 01:56:13AM -0500, Rich Felker wrote:
> I've looked into the "solution 4" that Solar proposed, which simply
> put is making __pthread_self() check for a clobbered thread register
> and restore it. While this sounds simple, there are a few issues I've
> run into whereby it starts to get ugly...
Some revisions... it's not quite as bad as I said, but still not good
either..
> with, but from reading the kernel sources, it looks like %fs is 0 and
> a hidden 64-bit offset is stored in a privileged register accessible
> only by the kernel (one which hopefully would not be clobbered by
> sigreturn, but I'm not sure...) when the thread pointer does not fit
> in 32 bits, and the old i386 method (LDT entry and non-zero %fs
> selector value) is used when the thread pointer fits in 32 bits. This
Got the cases reversed I think, but the issue still stands.
> pointer is valid, we can't restore it (and the value of %fs might
> actually need to differ per-thread if some threads are below the 4gb
> boundary and others are located above).
Per-thread difference is irrelevant since only the main thread can
ever experience this problem; all new threads start with a valid
thread pointer.
Rich
prev parent reply other threads:[~2012-02-25 13:32 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-10 2:58 Rich Felker
2012-02-10 7:40 ` Solar Designer
2012-02-10 7:58 ` Rich Felker
2012-02-10 10:42 ` Solar Designer
2012-02-10 11:22 ` Solar Designer
2012-02-10 17:00 ` Rich Felker
2012-02-10 19:12 ` Solar Designer
2012-02-25 6:56 ` Rich Felker
2012-02-25 13:32 ` Rich Felker [this message]
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