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Message-ID: <20121017015842.GX254@brightrain.aerifal.cx>
Date: Tue, 16 Oct 2012 21:58:42 -0400
From: Rich Felker <dalias@...ifal.cx>
To: musl@...ts.openwall.com
Subject: Re: TLS (thread-local storage) support
On Wed, Oct 17, 2012 at 03:49:33AM +0200, boris brezillon wrote:
> 2012/10/17 Rich Felker <dalias@...ifal.cx>:
> > On Wed, Oct 17, 2012 at 02:08:11AM +0200, boris brezillon wrote:
> >> >> I agree. This should be made optional. But if we don't compile libc
> >> >> with fsplit-stack (-fnosplit-stack).
> >> >> Each call to a libc func from an external func compiled with split
> >> >> stack may lead to a 64K stack chunk alloc.
> >> >
> >> > Where does this allocation take place from? There should simply be a
> >> > way to inhibit it.
> >> In the linker (gold linker).
> >
> > Well gold isn't running at runtime. I assume you mean it _arranges_
> > for this allocation to take place somehow, and that's what I'm
> > wondering about whether there's a way to avoid.
>
> The easiest way to avoid big stack chunk allocation is to compile musl
> with -fno-split-stack option.
> This will not add any overhead to functions (no split stack prolog)
> And this will add a note to the shared object which tells the linker
> to avoid __morestack to __morestack_non_split replacement.
Where is this documented? The GCC manual doesn't mention anything
about -fno-split-stack having special behavior like that, so for lack
of any documentation otherwise, it "should" just be the option to turn
off -fsplit-stack..
I'm not claiming you're wrong, just that this all seems poorly
documented.
Rich
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