%fs, %gs and ldt

[toposoph-space at yahoo.com]

Hi,

Is there any version of ABI which specifies %fs, %gs and ldt usage on
ia32 for *nix? Or any FreeBSD specification? I see that Nvidia driver
uses them, that there is some compatibility with Linux, that FreeBSD
kernel did not save %gs on context switch recently and not does %gs
processing, etc., etc. But I can not find what is the general idea of
using those things or what is intend for future usage.
Thank you in advance for any info,

Sergey.