Initialize FPU by default

[DCNick3]

Even though real operating systems will initialize FPU during their boot process (by issuing finit instruction), it would be more convenient for libcpu user if the FPU was already initialized.

[nepx]

Hello,

There's number of ways that the FPU can be initialized. Every operating system will do it differently -- for instance, OS/2 handles floating point exceptions using IRQ13. I added a routine that will do just that, but that's just the way that mine (Linux x86-64) does it. If it doesn't suit your needs (to simulate OS/2, for instance), you'll have to tinker with some of the bits yourself.

Alternatively, you can map a page to memory, write a bit of shellcode, and then execute it:

static uint8_t mem[4096];
static uint8_t data[] = { 0x0F, 0x20, 0xC0, 0x83, 0xE0, 0xF3, 0x83, 0xC8, 0x20, 0x0F, 0x22, 0xC0, 0xDB, 0xE3 };

/*
Disassembly, for those interested: 
0:  0f 20 c0                mov    eax,cr0
3:  83 e0 f3                and    eax,0xfffffff3 // ~(TS | EM)
6:  83 c8 20                or     eax,0x20
9:  0f 22 c0                mov    cr0,eax
c:  db e3                   fninit 
*/

static void* mem_stuff(uint32_t addr, int write)
{
    UNUSED(write);
    return mem + addr;
}

void setup_cpu(void)
{
    cpu_init();
    cpu_init_32bit();
    memcpy(mem, data, 14); 
    cpu_set_state(CPU_PHYSEIP, 0);
    cpu_register_mem_refill_handler(mem_stuff);
    cpu_run(5);
}