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Re: gcc 4.5 and TLS

On Tue, 20 Apr 2010, I wrote:

> and you need [glibc with NPTL] before you can build gcc with TLS.

Well, this isn't quite right. I'm told that you can get __thread support 
from gcc 4.5 without having to have NPTL support in your libc.

Problem is, that compiler will have fixed includes, libgcc, libstdc++ 
libraries etc all derived from and targeted at the system libc, which is 
not what you want, since this libc is from etch-m68k and lacks NPTL.

> This amounts to a circular dependency. When bootstrapping a cross 
> toolchain, the cycle is broken by building some libc object files early 
> and by building several compilers. Given a complete cross toolchain, 
> there are other solutions available.

One possible solution for a native build is, in sequence,

1. binutils
2. gcc
3. libc
4. gcc
5. libc

...installing each package as it is built, before building the next one. 

(I haven't tried this. Perhaps the TLS devs can chime in?)

Anyway, since these are native builds, steps 3+ need to happen running 
under a kernel with TLS support (which could be built with a plain 
etch-m68k tool chain last time I tried it). You also need the kernel 
headers from this kernel to be installed prior to step 3.

The best advice I've been given is to use a TLS/NPTL enabled cross 
tool-chain to build the complete libc, and simply install that (with 
kernel headers) in your chroot before building the native gcc.

To be sure, you'd then rebuild the whole of the buildd userland. And 
finally rebuild the whole tool-chain again in a clean new buildd made up 
of this new userland.


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