| To: | xen-devel@xxxxxxxxxxxxxxxxxxx |
|---|---|
| Subject: | [Xen-devel] mm.c: function virt_to_xen_l2e |
| From: | PUCCETTI Armand <armand.puccetti@xxxxxx> |
| Date: | 2006年7月20日 17:45:14 +0200 |
| Delivery-date: | 2006年7月20日 08:44:59 -0700 |
| Envelope-to: | www-data@xxxxxxxxxxxxxxxxxx |
| List-help: | <mailto:xen-devel-request@lists.xensource.com?subject=help> |
| List-id: | Xen developer discussion <xen-devel.lists.xensource.com> |
| List-post: | <mailto:xen-devel@lists.xensource.com> |
| List-subscribe: | <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe> |
| List-unsubscribe: | <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe> |
| Sender: | xen-devel-bounces@xxxxxxxxxxxxxxxxxxx |
| User-agent: | Thunderbird 1.5.0.4 (X11/20060615) |
I am trying to understand the function virt_to_xen_l2e.
The actual code in xen V3.0.1 begins with:
l2_pgentry_t *virt_to_xen_l2e(unsigned long v)
{
l4_pgentry_t *pl4e;
l3_pgentry_t *pl3e;
l2_pgentry_t *pl2e;
pl4e = &idle_pg_table[l4_table_offset(v)];
if ( !(l4e_get_flags(*pl4e) & _PAGE_PRESENT) )
{
pl3e = page_to_virt(alloc_xen_pagetable());
clear_page(pl3e);
*pl4e = l4e_from_paddr(__pa(pl3e), __PAGE_HYPERVISOR);
}
pl3e = l4e_to_l3e(*pl4e) + l3_table_offset(v);
... What puzzles me is pl3e. If I decompose the first expressionof the rhs of the last statement above, introducing some temporary vars, I get:
intpte_t a, b; physaddr_t c; a=(*pl4e).l4;b = (a & (PADDR_MASK & PAGE_MASK)); c = ((physaddr_t) b); pl3e= ((l3_pgentry_t *)__va(c)) + ...; // same line as original pl3e is apparently made by some arithmetic transformations and then a cast to a pointer. How do we know if the final address pl3e is defined, and the address it refers to is correct?? Same question about pl2e, as similar transformations are made to calculate it some lines
later. thanks for any insight. Armand _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
| <Prev in Thread] | Current Thread | [Next in Thread> |
|---|---|---|
| ||
| Previous by Date: | [Xen-devel] Daily Xen Builds , David F Barrera |
|---|---|
| Next by Date: | [Xen-devel] [RFC][Re: Xen Roadmap proposal] Grant table sockets , Michael LeMay |
| Previous by Thread: | [Xen-devel] [NET] gso: Fix reversed error test in netif_tx_trylock , Herbert Xu |
| Next by Thread: | [Xen-devel] [RFC][Re: Xen Roadmap proposal] Grant table sockets , Michael LeMay |
| Indexes: | [Date] [Thread] [Top] [All Lists] |