This is the code snippet, Sent the wrong one last time:
static int do_test_wp_bit(unsigned long vaddr)
{
char tmp_reg;
int flag;
__asm__ __volatile__(
" movb %0,%1 \n"
"1: movb %1,%0 \n"
" xorl %2,%2 \n"
"2: \n"
".section __ex_table,\"a\"\n"
" .align 4 \n"
" .long 1b,2b \n"
".previous \n"
:"=m" (*(char *) vaddr),
"=q" (tmp_reg),
"=r" (flag)
:"2" (1)
:"memory");
return flag;
}
On 6/29/08, Asim <linkasim@xxxxxxxxx> wrote:
> Hi,
>
> I made a custom kernel and it crashes at the below code snippet. Can
> any one explain whats being done in the below code. It comes from
> mm/init.c. The error I get on failure is :
>
> Checking if this processor honours the WP bit even in supervisor
> mode... Starting Phase 0Starting Phase 1.
> general protection fault: bb80 [#1]
> SMP
> Modules linked in:
> CPU: 0
> EIP: 0000:[<00000000>] Not tainted VLI
> EFLAGS: c014705c (2.6.18.8-xen #1)
> EIP is at rest_init+0x3fefe000/0x30
> eax: 00000000 ebx: 00030001 ecx: ffffffff edx: 00000000
> esi: 0000bb80 edi: 00000000 ebp: c03e9d9c esp: c03e9d90
> ds: 8325 es: 0061 ss: e021
>
> The code segment:
>
> void __init test_wp_bit(void)
> {
> /*
> * Ok, all PSE-capable CPUs are definitely handling the WP bit right.
> */
> const unsigned long vaddr = PAGE_OFFSET;
> pgd_t *pgd;
> pmd_t *pmd;
> pte_t *pte, old_pte;
>
> printk("Checking if this processor honours the WP bit even in
> supervisor mode... ");
>
> pgd = swapper_pg_dir + __pgd_offset(vaddr);
> pmd = pmd_offset(pgd, vaddr);
> pte = pte_offset(pmd, vaddr);
> old_pte = *pte;
> *pte = mk_pte_phys(0, PAGE_READONLY);
> local_flush_tlb();
>
> boot_cpu_data.wp_works_ok = do_test_wp_bit(vaddr);
>
> *pte = old_pte;
> local_flush_tlb();
>
> if (!boot_cpu_data.wp_works_ok) {
> printk("No.\n");
> #ifdef CONFIG_X86_WP_WORKS_OK
> panic("This kernel doesn't support CPU's with broken
> WP. Recompile it for a 386!");
> #endif
> } else {
> printk("Ok.\n");
> }
> }
>
>
> Regards,
> Asim
>
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