Mikael Pettersson wrote:
> Changing the API
> to use abstract "TLS indicies" would also require a call to return the
> "TLS base", which hardly seems like an improvement.
The TLS base can obviously be zero.
User-space asks to access TLS #n (for allocs #n can be -1).
The kernel maps that to GDT index #m.
The kernel stores #m in the user-space buffer.
User-space maps #m to a selector.
I'm missing why this is a substantial improvement over the current
interface (or functionally different at all). What does this proposal
let you do that the current one doesn't?
Look, I'm not saying the current API is perfect, far from it. But it does
have valid usage modes which are broken in x86-64's ia32 emulation, and
will break on i386 of you reallocate the TLS GDT indices. This is a fact.
Hm, well its a "fact" in that they use different segment descriptors,
but you'd be hard pressed to say that was a breakage. set_thread_area
was added in 2.5.29 (Jul 2002), and x86-64 added support in 2.5.43 (Oct
2002), so the current behaviour is pretty much as it has always been.
If you have a program that expects something different, you either wrote
it in Jul-Oct 2002, or you made an unsustainable assumption about how
set_thread_area() works.
Look, I'm not saying the current API is perfect, far from it. But it does
have valid usage modes which are broken in x86-64's ia32 emulation, and
will break on i386 of you reallocate the TLS GDT indices. This is a fact.
You seem to have a specific use-case in mind; do you have a program
which would like to use a new interface? Would you mind spelling it
out, and describe why the current interface doesn't work for you?
J
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