[LLVMdev] [llvm-commits] [Patch, RFC] Re: Adding support for explicitly specified TLS models (PR9788)

[Hans Wennborg]

On Fri, Jun 15, 2012 at 9:56 PM, Hans Wennborg <hans at chromium.org> wrote:
> (To the list this time..)
>
> On Fri, Jun 15, 2012 at 7:38 PM, Rafael Espíndola
> <rafael.espindola at gmail.com> wrote:
>>> The point still stands, though: that code requires the tls_model
>>> attribute to be respected; if the compiler chooses local-exec instead,
>>> it won't be dlopen-able.
>>
>> This is a fairly contrived use case, and an extension of a gcc extension.
>>
>>> I think it adds value to make the behaviour the same as GCC's. And
>>> it's not like the difference wouldn't be detectable: the asm is
>>> different, the .o files are different, and the code from the non-PIC
>>> i386 shared lib example wouldn't load with dlopen.
>>
>> The gcc behavior is inconsistent with the linker and, as you found
>> out, with itself.
>
> Yeah, but I've gotten more attached to the GCC behaviour the more I've
> thought about it :/
>
> I respect that you have more experience with both LLVM and the TLS
> stuff than me, though :)
>
>> Before you wrote
>>
>>> I don't have any more compelling reasons than those, and I don't feel
>>> super strongly about this, so I'm willing to give in if others
>>> disagree with me :)
>>
>> What about this:
>>
>> * We implement this first without a 'default' value. This covers the
>> one real world use case I know of (libc knowing it is not dlopened).
>> * I am to blame if we missed some other use case and commit to
>> implementing it in the future if/when it is found :-)
>
> OK, let's give it a couple more days and see if someone else chimes in
> or something new comes up. In the meantime, I'll rework the patch the
> way you've suggested and if nothing's changed we can land it by the
> end of next week. Sounds like a plan?

Attaching a new patch that has the behaviour we discussed.

The "globaldynamic" and default values have been merged, and LLVM will
start off with the user-specified model, but choose a more specific
one if possible.

Please review.

Thanks,
Hans
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