gdefs.h

The Valgrind distribution has multiple tools. The most popular is the memory checking tool (called M

         We want Memcheck to believe that the resulting flags are
         data-dependent on both CC_DEP1 and CC_DEP2, hence the 
         name DEP.

      CC_NDEP.  This is a 3rd argument to the operation which is
         sometimes needed.  We arrange things so that Memcheck does
         not believe the resulting flags are data-dependent on CC_NDEP
         ("not dependent").

   To make Memcheck believe that (the definedness of) the encoded
   flags depends only on (the definedness of) CC_DEP1 and CC_DEP2
   requires two things:

   (1) In the guest state layout info (amd64guest_layout), CC_OP and
       CC_NDEP are marked as always defined.

   (2) When passing the thunk components to an evaluation function
       (calculate_condition, calculate_eflags, calculate_eflags_c) the
       IRCallee's mcx_mask must be set so as to exclude from
       consideration all passed args except CC_DEP1 and CC_DEP2.

   Strictly speaking only (2) is necessary for correctness.  However,
   (1) helps efficiency in that since (2) means we never ask about the
   definedness of CC_OP or CC_NDEP, we may as well not even bother to
   track their definedness.

   When building the thunk, it is always necessary to write words into
   CC_DEP1 and CC_DEP2, even if those args are not used given the
   CC_OP field (eg, CC_DEP2 is not used if CC_OP is CC_LOGIC1/2/4).
   This is important because otherwise Memcheck could give false
   positives as it does not understand the relationship between the
   CC_OP field and CC_DEP1 and CC_DEP2, and so believes that the 
   definedness of the stored flags always depends on both CC_DEP1 and
   CC_DEP2.

   However, it is only necessary to set CC_NDEP when the CC_OP value
   requires it, because Memcheck ignores CC_NDEP, and the evaluation
   functions do understand the CC_OP fields and will only examine
   CC_NDEP for suitable values of CC_OP.

   A summary of the field usages is:

   Operation          DEP1               DEP2               NDEP
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

   add/sub/mul        first arg          second arg         unused

   adc/sbb            first arg          (second arg)
                                         XOR old_carry      old_carry

   and/or/xor         result             zero               unused

   inc/dec            result             zero               old_carry

   shl/shr/sar        result             subshifted-        unused
                                         result

   rol/ror            result             zero               old_flags

   copy               old_flags          zero               unused.


   Therefore Memcheck will believe the following:

   * add/sub/mul -- definedness of result flags depends on definedness
     of both args.

   * adc/sbb -- definedness of result flags depends on definedness of
     both args and definedness of the old C flag.  Because only two
     DEP fields are available, the old C flag is XOR'd into the second
     arg so that Memcheck sees the data dependency on it.  That means
     the NDEP field must contain a second copy of the old C flag
     so that the evaluation functions can correctly recover the second
     arg.

   * and/or/xor are straightforward -- definedness of result flags
     depends on definedness of result value.

   * inc/dec -- definedness of result flags depends only on
     definedness of result.  This isn't really true -- it also depends
     on the old C flag.  However, we don't want Memcheck to see that,
     and so the old C flag must be passed in NDEP and not in DEP2.
     It's inconceivable that a compiler would generate code that puts
     the C flag in an undefined state, then does an inc/dec, which
     leaves C unchanged, and then makes a conditional jump/move based
     on C.  So our fiction seems a good approximation.

   * shl/shr/sar -- straightforward, again, definedness of result
     flags depends on definedness of result value.  The subshifted
     value (value shifted one less) is also needed, but its
     definedness is the same as the definedness of the shifted value.

   * rol/ror -- these only set O and C, and leave A Z C P alone.
     However it seems prudent (as per inc/dec) to say the definedness
     of all resulting flags depends on the definedness of the result,
     hence the old flags must go in as NDEP and not DEP2.

   * rcl/rcr are too difficult to do in-line, and so are done by a
     helper function.  They are not part of this scheme.  The helper
     function takes the value to be rotated, the rotate amount and the
     old flags, and returns the new flags and the rotated value.
     Since the helper's mcx_mask does not have any set bits, Memcheck
     will lazily propagate undefinedness from any of the 3 args into 
     both results (flags and actual value).
*/
enum {
    AMD64G_CC_OP_COPY=0,  /* DEP1 = current flags, DEP2 = 0, NDEP = unused */
                          /* just copy DEP1 to output */

    AMD64G_CC_OP_ADDB,    /* 1 */
    AMD64G_CC_OP_ADDW,    /* 2 DEP1 = argL, DEP2 = argR, NDEP = unused */
    AMD64G_CC_OP_ADDL,    /* 3 */
    AMD64G_CC_OP_ADDQ,    /* 4 */

    AMD64G_CC_OP_SUBB,    /* 5 */
    AMD64G_CC_OP_SUBW,    /* 6 DEP1 = argL, DEP2 = argR, NDEP = unused */
    AMD64G_CC_OP_SUBL,    /* 7 */
    AMD64G_CC_OP_SUBQ,    /* 8 */

    AMD64G_CC_OP_ADCB,    /* 9 */
    AMD64G_CC_OP_ADCW,    /* 10 DEP1 = argL, DEP2 = argR ^ oldCarry, NDEP = oldCarry */
    AMD64G_CC_OP_ADCL,    /* 11 */
    AMD64G_CC_OP_ADCQ,    /* 12 */

    AMD64G_CC_OP_SBBB,    /* 13 */
    AMD64G_CC_OP_SBBW,    /* 14 DEP1 = argL, DEP2 = argR ^ oldCarry, NDEP = oldCarry */
    AMD64G_CC_OP_SBBL,    /* 15 */
    AMD64G_CC_OP_SBBQ,    /* 16 */

    AMD64G_CC_OP_LOGICB,  /* 17 */
    AMD64G_CC_OP_LOGICW,  /* 18 DEP1 = result, DEP2 = 0, NDEP = unused */
    AMD64G_CC_OP_LOGICL,  /* 19 */
    AMD64G_CC_OP_LOGICQ,  /* 20 */

    AMD64G_CC_OP_INCB,    /* 21 */
    AMD64G_CC_OP_INCW,    /* 22 DEP1 = result, DEP2 = 0, NDEP = oldCarry (0 or 1) */
    AMD64G_CC_OP_INCL,    /* 23 */
    AMD64G_CC_OP_INCQ,    /* 24 */

    AMD64G_CC_OP_DECB,    /* 25 */
    AMD64G_CC_OP_DECW,    /* 26 DEP1 = result, DEP2 = 0, NDEP = oldCarry (0 or 1) */
    AMD64G_CC_OP_DECL,    /* 27 */
    AMD64G_CC_OP_DECQ,    /* 28 */

    AMD64G_CC_OP_SHLB,    /* 29 DEP1 = res, DEP2 = res', NDEP = unused */
    AMD64G_CC_OP_SHLW,    /* 30 where res' is like res but shifted one bit less */
    AMD64G_CC_OP_SHLL,    /* 31 */
    AMD64G_CC_OP_SHLQ,    /* 32 */

    AMD64G_CC_OP_SHRB,    /* 33 DEP1 = res, DEP2 = res', NDEP = unused */
    AMD64G_CC_OP_SHRW,    /* 34 where res' is like res but shifted one bit less */
    AMD64G_CC_OP_SHRL,    /* 35 */
    AMD64G_CC_OP_SHRQ,    /* 36 */

    AMD64G_CC_OP_ROLB,    /* 37 */
    AMD64G_CC_OP_ROLW,    /* 38 DEP1 = res, DEP2 = 0, NDEP = old flags */
    AMD64G_CC_OP_ROLL,    /* 39 */
    AMD64G_CC_OP_ROLQ,    /* 40 */

    AMD64G_CC_OP_RORB,    /* 41 */
    AMD64G_CC_OP_RORW,    /* 42 DEP1 = res, DEP2 = 0, NDEP = old flags */
    AMD64G_CC_OP_RORL,    /* 43 */
    AMD64G_CC_OP_RORQ,    /* 44 */

    AMD64G_CC_OP_UMULB,   /* 45 */
    AMD64G_CC_OP_UMULW,   /* 46 DEP1 = argL, DEP2 = argR, NDEP = unused */
    AMD64G_CC_OP_UMULL,   /* 47 */
    AMD64G_CC_OP_UMULQ,   /* 48 */

    AMD64G_CC_OP_SMULB,   /* 49 */
    AMD64G_CC_OP_SMULW,   /* 50 DEP1 = argL, DEP2 = argR, NDEP = unused */
    AMD64G_CC_OP_SMULL,   /* 51 */
    AMD64G_CC_OP_SMULQ,   /* 52 */

    AMD64G_CC_OP_NUMBER
};

typedef
   enum {
      AMD64CondO      = 0,  /* overflow           */
      AMD64CondNO     = 1,  /* no overflow        */

      AMD64CondB      = 2,  /* below              */
      AMD64CondNB     = 3,  /* not below          */

      AMD64CondZ      = 4,  /* zero               */
      AMD64CondNZ     = 5,  /* not zero           */

      AMD64CondBE     = 6,  /* below or equal     */
      AMD64CondNBE    = 7,  /* not below or equal */

      AMD64CondS      = 8,  /* negative           */
      AMD64CondNS     = 9,  /* not negative       */

      AMD64CondP      = 10, /* parity even        */
      AMD64CondNP     = 11, /* not parity even    */

      AMD64CondL      = 12, /* jump less          */
      AMD64CondNL     = 13, /* not less           */

      AMD64CondLE     = 14, /* less or equal      */
      AMD64CondNLE    = 15, /* not less or equal  */

      AMD64CondAlways = 16  /* HACK */
   }
   AMD64Condcode;

#endif /* ndef __LIBVEX_GUEST_AMD64_DEFS_H */

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/*--- end                                 guest-amd64/gdefs.h ---*/
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