0.7.11.10:

[sbcl.git] / src / compiler / generic / early-objdef.lisp

diff --git a/src/compiler/generic/early-objdef.lisp b/src/compiler/generic/early-objdef.lisp
index 7407e4a..fb4deda 100644 (file)
--- a/src/compiler/generic/early-objdef.lisp
+++ b/src/compiler/generic/early-objdef.lisp
@@ -27,6 +27,15 @@
 ;;;   * LIST-POINTER-LOWTAG + 4 = OTHER-POINTER-LOWTAG: NIL is both a
 ;;;     cons and a symbol (at the same address) and depends on this.
 ;;;     See the definition of SYMBOL in objdef.lisp
+;;;   * OTHER-POINTER-LOWTAG > 4: Some code in the SPARC backend,
+;;;     which uses bit 2 of the ALLOC register to indicate that
+;;;     PSEUDO-ATOMIC is on, doesn't strip the low bits of reg_ALLOC
+;;;     before ORing in OTHER-POINTER-LOWTAG within a PSEUDO-ATOMIC
+;;;     section.
+;;; (These are just the ones we know about as of sbcl-0.7.1.22. There
+;;; might easily be more, since these values have stayed highly
+;;; constrained for more than a decade, an inviting target for
+;;; inventive abstraction-phobic maintainers.:-)
 (eval-when (:compile-toplevel :load-toplevel :execute)
   ;; The EVAL-WHEN is necessary (at least for Lispworks), because the
   ;; second DEFENUM uses the value of OTHER-IMMEDIATE-0-LOWTAG, which is