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Re: [RFC] Should we declare errno with __thread on x86?

From: Florian Weimer <fweimer at redhat dot com>
To: "H.J. Lu" <hjl dot tools at gmail dot com>
Cc: GNU C Library <libc-alpha at sourceware dot org>
Date: Wed, 13 Apr 2016 11:20:39 +0200
Subject: Re: [RFC] Should we declare errno with __thread on x86?
Authentication-results: sourceware.org; auth=none
References: <CAMe9rOrb8XPsTUKHMw7F-+iy7D=UH=5XP_K06wDAwka+RRDCgw at mail dot gmail dot com>

On 03/18/2016 10:42 PM, H.J. Lu wrote:

errno is defined in glibc as an TLS variable on x86,  Shouldn't we
declare it as

extern __thread int errno;

instead of

#   define errno (*__errno_location ())

to avoid function call overhead?

Considering that errno is mostly accessed on error paths, I think morecompact code is better. It's not obvious that TLS variable access is awin in all cases according to that metric.


Florian

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