Yeah, but my point is that two pointers can compare equal but point to different addresses, thus it's not necessarily a safe operation to dereference a pointer cast from `intptr_r`.
replyI don’t know what you mean, if you take the address of a thread local variable you get a regular pointer which is just as safe to dereference as any other pointer, cast through intprt_t or not?
replyIt's safe to dereference in the same thread.
replyA `thread_local`'s actual virtual address is not merely what the pointer contains - it's an offset from some other virtual address stored in the FS or GS register (on x86-64), which is swapped when you change thread. Casting the pointer to `intptr_t` does not retain the segment base address - only the offset. The pointer is not the absolute address.
If you dereference in another thread, it's the same offset, but from a different base address.
There may be other things besides segment registers on other architectures that also make it unsafe. The C standard makes no guarantee that you can safely dereference a pointer cast from `intptr_t`.
I’m sorry but this is just incorrect. When you take the address of a thread local variable you have to lookup its real address using something like __tls_get_addr or by reading its offset via fs/gs but once it’s in a pointer it’s just a regular absolute address and is fine to dereference on any thread. There is no separate type for a pointer to a thread local variable.
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