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Re: SUN TLS vs. GNU TLS (was Re: ELF TLS ABI vs L4 ABI)

From: Marcus Brinkmann
Subject: Re: SUN TLS vs. GNU TLS (was Re: ELF TLS ABI vs L4 ABI)
Date: Thu, 18 Nov 2004 19:52:05 +0100
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At Thu, 18 Nov 2004 19:33:04 +0100,
Espen Skoglund <address@hidden> wrote:
> [Marcus Brinkmann]
> > As ELF TLS is intended to be used via the __thread keyword, access
> > to it is done via the language features of the compiler, and can be
> > optimized at the compilers leisure.  In particular, GCC can either
> > load the thread pointer and use it with normal memory accesses, or
> > do all writes through the %gs segment register, or a mixture of
> > both.
> Sure, *if* gcc does recognize and "optimize" for the GNU ELF TLS
> standard, then it may access the TLS through %gs.  I was just assuming
> that the gcc folks were sane enough to not do this (which I hope is
> true).  This still doesn't get around optimizing all the hardcoded %gs
> stuff deep within glibc, though.

Check out the i386 config option TARGET_TLS_DIRECT_SEG_REGS in gcc CVS
HEAD.  There is an option to switch it on or off, but it is on by
default for GNU/Linux.

Or see also: http://gcc.gnu.org/ml/gcc-patches/2003-06/msg00402.html


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