Re: 9.0 RC1/Clang / illegal instruction (Signal 4) in gengtype while building cc_tools on i586.

On Sun, Oct 23, 2011 at 10:24:12AM +0200, Roman Divacky wrote:
> > Program received signal SIGILL, Illegal instruction.
> > 0x08048b24 in do_typedef (s=0x80532bf "CUMULATIVE_ARGS", pos=0x805e1a4)
> >     at /usr/src/gnu/usr.bin/cc/cc_tools/../../../../contrib/gcc/gengtype.c:103
> > 103     {
> > 
> > (gdb) disas 0x08048b24
> > Dump of assembler code for function do_typedef:
> > 0x08048b10 <do_typedef+0>:      push   %ebp
> > 0x08048b11 <do_typedef+1>:      mov    %esp,%ebp
> > 0x08048b13 <do_typedef+3>:      push   %ebx
> > 0x08048b14 <do_typedef+4>:      push   %edi
> > 0x08048b15 <do_typedef+5>:      push   %esi
> > 0x08048b16 <do_typedef+6>:      sub    $0xc,%esp
> > 0x08048b19 <do_typedef+9>:      mov    $0x805e1d4,%edi
> > 0x08048b1e <do_typedef+14>:     mov    0x10(%ebp),%esi
> > 0x08048b21 <do_typedef+17>:     mov    0x8(%ebp),%ebx
> > 0x08048b24 <do_typedef+20>:     nopw   %cs:0x0(%eax,%eax,1)
> 
> LLVM attempts to use an optimal nop sequence when writing N-byte nop,
> by using these nop instructions
> 
>   static const uint8_t Nops[10][10] = {
>     // nop
>     {0x90},
>     // xchg %ax,%ax
>     {0x66, 0x90},
>     // nopl (%[re]ax)
>     {0x0f, 0x1f, 0x00},
>     // nopl 0(%[re]ax)
>     {0x0f, 0x1f, 0x40, 0x00},
>     // nopl 0(%[re]ax,%[re]ax,1)
>     {0x0f, 0x1f, 0x44, 0x00, 0x00},
>     // nopw 0(%[re]ax,%[re]ax,1)
>     {0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00},
>     // nopl 0L(%[re]ax)
>     {0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00},
>     // nopl 0L(%[re]ax,%[re]ax,1)
>     {0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
>     // nopw 0L(%[re]ax,%[re]ax,1)
>     {0x66, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
>     // nopw %cs:0L(%[re]ax,%[re]ax,1)
>     {0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
>   };
> 
> There's no checking for a supported CPU, is it so that AMD geode doesnt support any of these?
> Any other cpu that doesnt support these? If this is CPU dependant, I suggest to open a bug
> report upstream as it's a bug.

Long nops are supported only on specific CPUs. Unconditional use of them
is a plain bug, like unconditional use of cmovXX.