[Lightning] Segmentation fault on linux i686

[Jondy Zhao]

Hi,

I build lightning 2.1.2 in linux i686, all the examples in the doc work, but 
`doc/ifib` and `doc/rfib` failed: Segmentation fault

I add extra line `jit_disassemble();` in the file `doc/ifib.c`, here it's output

        0xb7596000      sub    $0x10,%esp
        0xb7596003      mov    %ebx,0x4(%esp)
        0xb7596007      mov    %ebp,(%esp)
        0xb759600a      mov    %esp,%ebp
        0xb759600c      sub    $0x1c,%esp
        0xb759600f      mov    0x14(%ebp),%eax
        0xb7596012      test   %ecx,(%edi)
        0xb7596014      test   %ah,(%edi)
        0xb7596016      add    %al,(%eax)
        0xb7596018      add    %cl,0x1b8c1(%ecx)
        0xb759601e      add    %al,(%eax)
        0xb7596020      cmp    $0x2,%ecx
        0xb7596023      jle    0xb7596040
        0xb7596029      lea    -0x2(%ecx),%edx
        0xb759602c      mov    %eax,%ecx
        0xb759602e      xchg   %ax,%ax
        0xb7596030      sub    $0x1,%edx
        0xb7596033      mov    %eax,%ebx
        0xb7596035      add    %ecx,%eax
        0xb7596037      mov    %ebx,%ecx
        0xb7596039      test   %ecx,(%edi)
        0xb759603b      test   %esi,%eax
        0xb759603d      (bad)
        0xb759603e      (bad)
        0xb759603f      decl   0x245c8bec(%ecx)
        0xb7596045      add    $0x8b,%al
        0xb7596047      sub    $0x24,%al
        0xb7596049      add    $0x10,%esp
        0xb759604c      ret

It seems something is wrong with `jit_patch`, there are bad instructions.

Any ideas?

I run these commands in a vbox virtual machine:

$ uname -a
Linux ubuntu32 4.8.0-22-generic #24-Ubuntu SMP Sat Oct 8 09:14:42 UTC 2016 i686 
i686 i686 GNU/Linux

$ gcc --version
gcc (Ubuntu 6.2.0-5ubuntu12) 6.2.0 20161005

Regards
Jondy