A Null Pointer Dereference Bug

We find a NPD bug in function ppc32_icbi
First, the function ppc32_jit_find_by_phys_page may return a NULL value.

static inline ppc32_jit_tcb_t *
ppc32_jit_find_by_phys_page(cpu_ppc_t *cpu,m_uint32_t phys_page)
{
   m_uint32_t page_hash =  ppc32_jit_get_phys_hash(phys_page);
   ppc32_jit_tcb_t *block;

   for(block=cpu->exec_phys_map[page_hash];block;block=block->phys_next)
      if (block->phys_page == phys_page)
         return block;

   return NULL;
}

Then in function ppc32_icbi, if DEBUG_ICBI is defined and block is NULL, there would be a NULL pointer dereference bug.

void ppc32_icbi(cpu_ppc_t *cpu,m_uint32_t vaddr,u_int op)
{
   ppc32_jit_tcb_t *block;
   m_uint32_t phys_page;

#if DEBUG_ICBI
   cpu_log(cpu->gen,"MTS","ICBI: ia=0x%8.8x, vaddr=0x%8.8x\n",cpu->ia,vaddr);
#endif

   if (!cpu->translate(cpu,vaddr,PPC32_MTS_ICACHE,&phys_page)) {
      if (cpu->exec_phys_map) {
         block = ppc32_jit_find_by_phys_page(cpu,phys_page);

         if (block && (block->start_ia == (vaddr & PPC32_MIN_PAGE_MASK))) {
#if DEBUG_ICBI
            cpu_log(cpu->gen,"MTS",
                    "ICBI: removing compiled page at 0x%8.8x, pc=0x%8.8x\n",
                    block->start_ia,cpu->ia);
#endif
            ppc32_jit_tcb_free(cpu,block,TRUE);
            cpu->exec_blk_map[ppc32_jit_get_ia_hash(vaddr)] = NULL;
         }
         else
         {
#if DEBUG_ICBI
            cpu_log(cpu->gen,"MTS",
                    "ICBI: trying to remove page 0x%llx with pc=0x%llx\n",
                    block->start_ia,cpu->is);         //NPD here
#endif
         }
      }
   }
}

Start at the ppc32_icbi entry point and inspect its call to ppc32_jit_find_by_phys_page, especially the DEBUG_ICBI logging path. Verify the behavior when the lookup returns NULL and confirm that the completed change handles that case without dereferencing block, with the diagnostic path still working.