Re: [Yap-users] yap-6.2.2 fails to buld on i686 with GCC 7

[Petr P. <pp...@re...>]

On Mon, Feb 13, 2017 at 02:53:07PM +0100, Petr Pisar wrote:
> Hello, when building yap-6.2.2 with GCC 7, I obtain this build failure on i686
> only:
[...] 
> Do you have any idea what's wrong? I guess GCC 7 brought some new
> optimizations that leads to misbehaving code.
> 
After compiling the code with -fsanitize=undefined compiler option, I can see
these warnings:

C/scanner.c:567:17: runtime error: signed integer overflow: 268435453 * 16 cannot be represented in type 'int'
H/Yatom.h:161:39: runtime error: member access within misaligned address 0x1005c299 for type 'struct FunctorEntry', which requires 4 byte alignment
H/Yatom.h:161:39: runtime error: member access within misaligned address 0x10120631 for type 'struct FunctorEntry', which requires 4 byte alignment
H/Yatom.h:161:39: runtime error: member access within misaligned address 0x10120631 for type 'struct FunctorEntry', which requires 4 byte alignment
H/Yatom.h:161:39: runtime error: member access within misaligned address 0x10120631 for type 'struct FunctorEntry', which requires 4 byte alignment
H/Yatom.h:161:39: runtime error: member access within misaligned address 0x10120631 for type 'struct FunctorEntry', which requires 4 byte alignment
H/Yatom.h:161:39: runtime error: member access within misaligned address 0x10120631 for type 'struct FunctorEntry', which requires 4 byte alignment
H/Yatom.h:161:39: runtime error: member access within misaligned address 0x10120631 for type 'struct FunctorEntry', which requires 4 byte alignment
H/Yatom.h:161:39: runtime error: member access within misaligned address 0x10120631 for type 'struct FunctorEntry', which requires 4 byte alignment
H/Yatom.h:161:39: runtime error: member access within misaligned address 0x10063889 for type 'struct FunctorEntry', which requires 4 byte alignment
H/Yatom.h:161:39: runtime error: member access within misaligned address 0x10063889 for type 'struct FunctorEntry', which requires 4 byte alignment
H/Yatom.h:161:39: runtime error: member access within misaligned address 0x10063889 for type 'struct FunctorEntry', which requires 4 byte alignment
C/absmi.c:12286:4: runtime error: member access within misaligned address 0x101e6e52 for type 'struct yami', which requires 4 byte alignment

Because i686 allows unaliagned access, I think a problem could be the signed integer overflow in get_num() at C/scanner.c:567:

  Int val = 0L;
  [...]

  } else if (ch == 'x' && base == 0) {
    might_be_float = FALSE;
    if (--max_size == 0) {
      Yap_ErrorMessage = "Number Too Long";
      return TermNil;
    }
    *sp++ = ch;
    ch = Nxtch(inp_stream);
    while (my_isxdigit(ch, 'F', 'f')) {
      Int oval = val;
      int chval = (chtype(ch) == NU ? ch - '0' :
                   (my_isupper(ch) ? ch - 'A' : ch - 'a') + 10);
      if (--max_size == 0) {
        Yap_ErrorMessage = "Number Too Long";
        return TermNil;
      }
      *sp++ = ch;
→     val = val * 16 + chval;
      if (oval != (val-chval)/16) /* overflow */
        has_overflow = TRUE;
      ch = Nxtch(inp_stream);
    }
    *chp = ch;
  }

-- Petr