[llvm-dev] [PPC] Linker fails on -fstack-protector

Tim Shen via llvm-dev llvm-dev at lists.llvm.org
Tue Feb 23 08:39:50 PST 2016

On Tue, Feb 23, 2016, 04:50 Joerg Sonnenberger via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> You can get the TCB address from %fs:0 or %gs:0 on x86. But that's
> suboptimal for the purpose here as you need to do a second load with the
> resulting pointer, when you could have gotten it from %fs:$magic_offset
> or %gs:$magic_offset in first place.

Isn't LLVM already combining a register load with an offset (0) followed by
another offset-load? If it's currently not implemented, it seems quite
useful and generic, and we should just implmenet it?

If for some reason it can't be done, we can still pass the offset into the
intrinsic, as ISD::GlobalTLSAddress is designed.

ISD::GlobalTLSAddress is actually quite close to what we want - except for
a GlobalValue it requires. Maybe we can make that requirement optional?
E.g. if a nullptr is passed in as the GlobalValue, generate fs:offset,
rather than fs:@a+ offset.
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