src/compiler/generic/early-vm.lisp

   1 ;;;; This software is part of the SBCL system. See the README file for
   2 ;;;; more information.
   3 ;;;;
   4 ;;;; This software is derived from the CMU CL system, which was
   5 ;;;; written at Carnegie Mellon University and released into the
   6 ;;;; public domain. The software is in the public domain and is
   7 ;;;; provided with absolutely no warranty. See the COPYING and CREDITS
   8 ;;;; files for more information.
   9
  10 (in-package "SB!VM")
  11
  12 ;;; the number of bits per byte, where a byte is the smallest
  13 ;;; addressable object
  14 (defconstant n-byte-bits 8)
  15
  16 ;;; the number of bits at the low end of a pointer used for type
  17 ;;; information
  18 (defconstant n-lowtag-bits
  19   (integer-length (1- (/ (* 2 n-word-bits) n-byte-bits))))
  20 ;;; a mask to extract the low tag bits from a pointer
  21 (defconstant lowtag-mask (1- (ash 1 n-lowtag-bits)))
  22 ;;; the exclusive upper bound on the value of the low tag bits from a
  23 ;;; pointer
  24 (defconstant lowtag-limit (ash 1 n-lowtag-bits))
  25 ;;; the number of tag bits used for a fixnum
  26 (defconstant n-fixnum-tag-bits
  27   ;; On 64-bit targets, this may be as low as 1 (for 63-bit
  28   ;; fixnums) and as high as 3 (for 61-bit fixnums).  The
  29   ;; constraint on the low end is that we need at least one bit
  30   ;; to determine if a value is a fixnum or not, and the
  31   ;; constraint on the high end is that it must not exceed
  32   ;; WORD-SHIFT (defined below) due to the use of unboxed
  33   ;; word-aligned byte pointers as boxed values in various
  34   ;; places.  FIXME: This should possibly be exposed for
  35   ;; configuration via customize-target-features.
  36   #!+64-bit 1
  37   ;; On 32-bit targets, this may be as low as 2 (for 30-bit
  38   ;; fixnums) and as high as 2 (for 30-bit fixnums).  The
  39   ;; constraint on the low end is simple overcrowding of the
  40   ;; lowtag space, and the constraint on the high end is that it
  41   ;; must not exceed WORD-SHIFT.
  42   #!-64-bit (1- n-lowtag-bits))
  43 ;;; the fixnum tag mask
  44 (defconstant fixnum-tag-mask (1- (ash 1 n-fixnum-tag-bits)))
  45 ;;; the bit width of fixnums
  46 (defconstant n-fixnum-bits (- n-word-bits n-fixnum-tag-bits))
  47 ;;; the bit width of positive fixnums
  48 (defconstant n-positive-fixnum-bits (1- n-fixnum-bits))
  49
  50 ;;; the number of bits to shift between word addresses and byte addresses
  51 (defconstant word-shift (1- (integer-length (/ n-word-bits n-byte-bits))))
  52
  53 ;;; the number of bytes in a word
  54 (defconstant n-word-bytes (/ n-word-bits n-byte-bits))
  55
  56 ;;; the number of bytes in a machine word
  57 (defconstant n-machine-word-bytes (/ n-machine-word-bits n-byte-bits))
  58
  59 ;;; the number of bits used in the header word of a data block to store
  60 ;;; the type
  61 (defconstant n-widetag-bits 8)
  62 ;;; a mask to extract the type from a data block header word
  63 (defconstant widetag-mask (1- (ash 1 n-widetag-bits)))
  64
  65 (defconstant sb!xc:most-positive-fixnum
  66     (1- (ash 1 n-positive-fixnum-bits))
  67   "the fixnum closest in value to positive infinity")
  68 (defconstant sb!xc:most-negative-fixnum
  69     (ash -1 n-positive-fixnum-bits)
  70   "the fixnum closest in value to negative infinity")
  71
  72 (defconstant most-positive-word (1- (expt 2 n-word-bits))
  73   "The most positive integer that is of type SB-EXT:WORD.")
  74
  75 (defconstant most-positive-exactly-single-float-fixnum
  76   (min (expt 2 single-float-digits) sb!xc:most-positive-fixnum))
  77 (defconstant most-negative-exactly-single-float-fixnum
  78   (max (- (expt 2 single-float-digits)) sb!xc:most-negative-fixnum))
  79 (defconstant most-positive-exactly-double-float-fixnum
  80   (min (expt 2 double-float-digits) sb!xc:most-positive-fixnum))
  81 (defconstant most-negative-exactly-double-float-fixnum
  82   (max (- (expt 2 double-float-digits)) sb!xc:most-negative-fixnum))
  83
  84 ;;;; Point where continuous area starting at dynamic-space-start bumps into
  85 ;;;; next space.
  86 #!+gencgc
  87 (defconstant max-dynamic-space-end
  88     (let ((stop (1- (ash 1 n-word-bits)))
  89           (start dynamic-space-start))
  90       (dolist (other-start (list read-only-space-start static-space-start
  91                                  #!+linkage-table
  92                                  linkage-table-space-start))
  93         (declare (notinline <)) ; avoid dead code note
  94         (when (< start other-start)
  95           (setf stop (min stop other-start))))
  96       stop))
  97
  98 ;; The lowest index that you can pass to %INSTANCE-REF accessing
  99 ;; a slot of data that is not the instance-layout.
 100 ;; To get a layout, you must call %INSTANCE-LAYOUT - don't assume index 0.
 101 (defconstant instance-data-start (+ #!-compact-instance-header 1))
 102
 103 ;; The largest number that may appear in the header-data for an instance,
 104 ;; and some other mostly-boxed objects, such as FDEFNs.
 105 ;; This constraint exists because for objects managed by the immobile GC,
 106 ;; their generation number is stored in the header, so we have to know
 107 ;; how much to mask off to obtain the payload size.
 108 ;; Objects whose payload gets capped to this limit are considered
 109 ;; "short_boxed" objects in the sizetab[] array in 'gc-common'.
 110 ;; Additionally there are "tiny_boxed" objects, the payload length of
 111 ;; which can be expressed in 8 bits.
 112 (defconstant short-header-max-words #x7fff)
 113
 114 ;; A string tagged as +STRING-SHAREABLE+ is logically readonly,
 115 ;; and permitted to be shared with another string per the CLHS standard
 116 ;; under the concept of similarity as constant. A string so tagged is
 117 ;; often the print-name of a symbol, or was loaded from a fasl,
 118 ;; or used in a few others situations that warrant sharing.
 119 (def!constant +string-shareable+ 2)
 120
 121 ;; A string tagged as +STRING-SHAREABLE-NONSTD+ is logically readonly,
 122 ;; and *not* technically permitted by the standard to be shared.
 123 ;; If, despite the apparent prohibition, the user opts to make these
 124 ;; shareable, we'll do it. This typically occurs with compilation
 125 ;; into memory, where the requirement is that the machine code
 126 ;; reference "the same" object as appeared in source, but where,
 127 ;; nonetheless, opportunities for sharing abound.
 128 (def!constant +string-shareable-nonstd+ 4)
 129
 130 ;;; Is X a fixnum in the target Lisp?
 131 #+sb-xc-host
 132 (defun fixnump (x)
 133   (and (integerp x)
 134        (<= sb!xc:most-negative-fixnum x sb!xc:most-positive-fixnum)))
 135
 136 ;;; Helper macro for defining FIXUP-CODE-OBJECT so that its body
 137 ;;; can be the same between the host and target.
 138 ;;; In the target, the byte offset supplied is relative to CODE-INSTRUCTIONS.
 139 ;;; Genesis works differently - it adjusts the offset so that it is relative
 140 ;;; to the containing gspace since that's what bvref requires.
 141 (defmacro !with-bigvec-or-sap (&body body)
 142   `(macrolet #-sb-xc-host ()
 143              #+sb-xc-host
 144              ((code-instructions (code) `(sb!fasl::descriptor-mem ,code))
 145               (sap-int (sap)
 146                 ;; KLUDGE: SAP is a bigvec; it doesn't know its address.
 147                 ;; Note that this shadows the uncallable stub function for SAP-INT
 148                 ;; that placates the host when compiling 'compiler/*/move.lisp'.
 149                 (declare (ignore sap))
 150                 `(locally
 151                      (declare (notinline sb!fasl::descriptor-gspace)) ; fwd ref
 152                    (sb!fasl::gspace-byte-address
 153                     (sb!fasl::descriptor-gspace code)))) ; use CODE, not SAP
 154               (sap-ref-8 (sap offset) `(sb!fasl::bvref-8 ,sap ,offset))
 155               (sap-ref-32 (sap offset) `(sb!fasl::bvref-32 ,sap ,offset))
 156               (sap-ref-word (sap offset) `(sb!fasl::bvref-word ,sap ,offset)))
 157      ,@body))