+;;; this isn't actually a lisp object at all, it's a c structure that lives
+;;; in c-land. However, we need sight of so many parts of it from Lisp that
+;;; it makes sense to define it here anyway, so that the GENESIS machinery
+;;; can take care of maintaining Lisp and C versions.
+;;; Hence the even-fixnum lowtag just so we don't get odd(sic) numbers
+;;; added to the slot offsets
+(define-primitive-object (thread :lowtag even-fixnum-lowtag)
+ ;; unbound_marker is borrowed very briefly at thread startup to
+ ;; pass the address of initial-function into new_thread_trampoline
+ (unbound-marker :init :unbound) ; tls[0] = UNBOUND_MARKER_WIDETAG
+ (pid :c-type "pid_t")
+ (binding-stack-start :c-type "lispobj *" :length #!+alpha 2 #!-alpha 1)
+ (binding-stack-pointer :c-type "lispobj *" :length #!+alpha 2 #!-alpha 1)
+ (control-stack-start :c-type "lispobj *" :length #!+alpha 2 #!-alpha 1)
+ (control-stack-end :c-type "lispobj *" :length #!+alpha 2 #!-alpha 1)
+ (alien-stack-start :c-type "lispobj *" :length #!+alpha 2 #!-alpha 1)
+ (alien-stack-pointer :c-type "lispobj *" :length #!+alpha 2 #!-alpha 1)
+ #!+gencgc (alloc-region :c-type "struct alloc_region" :length 5)
+ (tls-cookie) ; on x86, the LDT index
+ (this :c-type "struct thread *" :length #!+alpha 2 #!-alpha 1)
+ (next :c-type "struct thread *" :length #!+alpha 2 #!-alpha 1)
+ #!+x86 (pseudo-atomic-atomic)
+ #!+x86 (pseudo-atomic-interrupted)
+ (interrupt-data :c-type "struct interrupt_data *"
+ :length #!+alpha 2 #!-alpha 1)
+ (interrupt-contexts :c-type "os_context_t *" :rest-p t))