[Xen-users] Re: Xen and TLS, -mno-tls-direct-seg-refs needed?

[Sven Köhler <skoehler@xxxxxx>]

>> If i have a multilib x86_64 system (that means: 64-bit glibc and
>> 32-bit glibc are present), then the 32-bit does still needs this
>> -mno-tls-direct-seg-refs neede - or does it not?
> 
> I honestly have NO idea.
> 
> I would imagine that it works like this:
> 
> Since the CPU is running in 64-bit mode by virtue of you running a
> 64-bit OS, any 32-bit code is executed in a fashion where the
> operating system has first told the CPU to set up a virtual 4GB 32-bit
> environment.  Any kernel calls from 32-bit code goes into a
> translation layer the kernel has, and the translation layer knows how
> to switch the CPU to 64-bit mode to actually perform the kernel call
> onto the 64-bit kernel.  Xen would live entirely outside of the 4 GB
> virtual 32-bit area, being used only from the 64-bit kernel, and being
> protected by whatever mechanism it is that Xen normally uses on
> x86_64.

Yes, but what you describe is kernel-internal. But the
"-mno-tls-direct-seg-refs" is glibc-specific and changes glibc-internal
things, not kernel-internal things.

So if the 64-bit kernel allows the 32-bit glibc to access the TLS-data
the usual way, and if the 64-Bit Xen also has the problems with that
usual way, then the "-mno-tls-direct-seg-refs" might be needed.

But who knows? :-)

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