[gentoo-dev] Re: why I do not have /usr/lib/tls on my gentoo?

[gentoo-dev] Re: why I do not have /usr/lib/tls on my gentoo?

[Duncan]

David Shen <davidshen84@googlemail.com> posted
53e35fd50906190041j35d95488lbcf3c7eb1efa87fb@mail.gmail.com, excerpted
below, on  Fri, 19 Jun 2009 15:41:30 +0800:

> I am trying to install Xen VM on my gentoo 2008 x64. According to what
> http://en.gentoo-wiki.com/wiki/Xen said, I should run "mv /usr/lib/tls
> /usr/lib/tls.disabled" and re-compile glibc and gcc to disable the 'tls'
> feature. But I found that my system *DOES NOT* have the /usr/lib/tls
> file/directory. Does this changed its place, or this prerequisite does
> not apply to x64 system?

First, note for future reference that "x64" is a rather ambiguous term, 
as it's (AFAIK) unofficial and could be equally argued to apply to 
Intel's ia64 aka "itanium" aka "itanic" architecture or to AMD's amd64 
aka x86_64 architecture.  Of course, this list is for the amd64 arch and 
it can be assumed you are referring to that here, but as I said, for 
future reference. =:^O

Meanwhile, to your question:  I don't do xen but based on my knowledge of 
Gentoo and Linux history from the 2004 time frame, that doesn't apply to 
a modern Gentoo Linux system.

"tls" refers to "thread local storage".

I'm somewhat confused on the exact relationships (whether tls was the 
nptl on or off version, a google produced some hints that it was the nptl 
on version, but nothing definitive), but tls was related to nptl, "native 
posix thread library", which was introduced by Red Hat back in 2002 and 
was just becoming a big thing on Gentoo about the time I switched to 
Gentoo around May, 2004.  Prior to that, Linux had normally used Linux 
threads for threading. However, Linux-threads was Linux-only and wasn't 
entirely POSIX compatible, among other issues.  NPTL was higher 
performing, and gradually took over and became the standard, both due to 
the better performance and because it WAS POSIX compliant and therefore 
made easier porting between Linux and the BSDs and various UNIX variants.

NPTL did/does require either a 2.6 kernel or a patched 2.4 kernel, and 
was supported by glibc.  Just checking the older glibc versions still in 
the tree, thru glibc 2.5*, the Gentoo glibc ebuilds have the nptl and 
nptlonly USE flags.  With glibc 2.6, Gentoo was apparently dropping 
mainline kernel 2.4 support and nptl (and nptlonly) apparently became the 
un-USE-flagged default.

Anyway, back when glibc was built for both nptl and linux-threads, 
/usr/lib/tls contained one version, while the other was in the standard 
/lib and /usr/lib locations (where lib means lib64 on amd64, with an 
equivalent 32-bit version for multilib users).

BTW, x86(32) and amd64 no-multilib users now build glibc only once, while 
amd64 multilib users (the default) build it twice, once for 32-bit and 
once for 64-bit.  During the linux-threads/nptl both era, that was 
doubled, so amd64 multilib users were actually building glibc four times, 
one each for nptl and linux-threads, for each of 32-bit and 64-bit!  No 
WONDER emerging glibc seemed to take so long back then!

So assuming you're using a 2.6 kernel and glibc >= 2.6 as well, 
/usr/lib(64)/tls should not exist, unless for some reason it wasn't 
removed properly during whatever glibc emerge would have gotten rid of it 
(the first 2.6 version if users hadn't been running USE=nptl nptlonly, 
the first glibc emerge after they switched to those USE flags if they did 
run them).  The same should apply to the corresponding 32-bit libdir, for 
those still running multilib (I'm running no-multilib and don't remember 
where the 32-bit dir was, anymore).

Thus, apparently that step of the the xen guide is either still around 
for the legacy installs still using old glibc versions, or it's there to 
ensure people remove the dir if it's unused cruft that didn't get cleaned 
up properly for whatever reason.  Since you don't have that dir, you 
shouldn't have to worry about it.

Here's some wikipedia links that should serve as beginning points for 
further research, if you're curious:

http://en.wikipedia.org/wiki/Thread-local_storage
http://en.wikipedia.org/wiki/Nptl
http://en.wikipedia.org/wiki/LinuxThreads (stub article)

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman