X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=base-target-features.lisp-expr;h=5b97f7295761437ba5dc5e439a4d482f78295d0e;hb=c27ee1dba86042cb431c298699c19ed3fcd70026;hp=c6e3c90197ceeca26180a10ce38d772894b70139;hpb=be76f6319dcb41477209676e6f26e0030e4659ba;p=sbcl.git

diff --git a/base-target-features.lisp-expr b/base-target-features.lisp-expr
index c6e3c90..5b97f72 100644
--- a/base-target-features.lisp-expr
+++ b/base-target-features.lisp-expr
@@ -157,18 +157,23 @@
  ;; As of SBCL 0.8,  this is only supposed to work in x86 Linux, on which
  ;; system it's implemented using clone(2) and the %fs segment register.
  ;; Note that no consistent effort to audit the SBCL library code for
- ;; thread safety has been performed, so caveat executor
+ ;; thread safety has been performed, so caveat executor.
  ; :sb-thread
+
+ ;; Kernel support for futexes (so-called "fast userspace mutexes") is
+ ;; available in Linux 2.6 and some versions of 2.4 (Red Hat vendor
+ ;; kernels, possibly other vendors too).  We can take advantage of
+ ;; these to do faster and probably more reliable mutex and condition
+ ;; variable support.  An SBCL built with this feature will fall back
+ ;; to the old system if the futex() syscall is not available at
+ ;; runtime
+ ; :sb-futex
  
  ;; This affects the definition of a lot of things in bignum.lisp. It
  ;; doesn't seem to be documented anywhere what systems it might apply
  ;; to. It doesn't seem to be needed for X86 systems anyway.
  ; :32x16-divide
 
- ;; This is probably true for some processor types, but not X86. It
- ;; affects a lot of floating point code.
- ; :negative-zero-is-not-zero
-
  ;; This is set in classic CMU CL, and presumably there it means
  ;; that the floating point arithmetic implementation
  ;; conforms to IEEE's standard. Here it definitely means that the
@@ -199,6 +204,10 @@
  ;; in the *FEATURES* list
  ;;
 
+ ;; Any target feature which affects binary compatibility of fasl files
+ ;; needs to be recorded in *FEATURES-POTENTIALLY-AFFECTING-FASL-FORMAT*
+ ;; (elsewhere).
+
  ;; notes on the :NIL and :IGNORE features:
  ;;
  ;; #+NIL is used to comment out forms. Occasionally #+IGNORE is used