Hi,

I would like to _try_ to add ELF64 Thread Local Storage support to fasmg.

Since my knowledge about fasm internals is zero and I only did scratch the surface of the fasmg macro language, I am unable to see if there are obvious show stoppers in those very internals and/or the macro language misses some critical features.

Any pointers/help/warnings/etc?

I regret that I have not finished the second chapter of my formats tutorial, as it could be a perfect reference here. But I believe even the first one (about PE) can be a good source of inspiration, showing how to build various format structure with only basic macro features. As demonstrated there, you do not really need any advanced tricks most of the time, only the very basics of fasmg's macro language.

Thanks for your time, response, and pointers. I have been sidetracked on others topics. I'll probably be back later on this matter.
Nethertheless I did go deeper in tls, and the only reasonable way to deal "properly" with it is the "dynamic" way (tls specs from ulrich drepper): the location of tls data must use a dynamic linker ABI function for such task (because of lazy tls). It should be reduced to calling this dynamic linker function with some "offsets/ids" which would be provided via some relocation entries of tls types.
tls was a very bad idea in the first place, really bad. sad much software does rely on it (i.e. glibc) for their implementation.