From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcus Granado Subject: Re: [PATCH 2/3] xenoprof: Handle 32-bit guest stacks properly in a 64-bit hypervisor Date: Tue, 24 Jan 2012 19:27:38 +0000 Message-ID: <4F1F062A.4080306@citrix.com> References: <4F19B62C.9020402@citrix.com> <4F1D3B79020000780006E509@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4F1D3B79020000780006E509@nat28.tlf.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jan Beulich Cc: George Dunlap , xen-devel List-Id: xen-devel@lists.xenproject.org On 23/01/12 09:50, Jan Beulich wrote: > If you're adding a compat mode guest case here, then you should > also use compat mode accessors (compat_handle_okay(), > __copy_from_compat_offset()), implying that you also have a local > handle variable of the appropriate type (and perhaps moving the > native one down into the 'else' body). I'm trying to understand the compat handle. It is not clear to me how to map one from head (a 64-bit pointer), since COMPAT_HANDLE seems to store a 32-bit compat_ptr_t value in its structure. Ideally, what I would like to do is COMPAT_HANDLE(char) guest_head = map_guest_handle_to_compat_handle (guest_handle_from_ptr(head, char)); or COMPAT_HANDLE(char) guest_head = compat_handle_from_ptr(head, char)); but I can't find any equivalent functions in any header. The following line compiles, COMPAT_HANDLE(char) guest_head = { (full_ptr_t)head }; but it looks like, in this case, the compat handle structure in compat.h will truncate the most significant bits from the head pointer, so compat_handle_okay(guest_head,...) and __copy_from_compat(...,guest_head,...) below will be using a truncated pointer: 56 static struct frame_head * 57 dump_guest_backtrace(struct domain *d, struct vcpu *vcpu, 58 struct frame_head * head, int mode) 59 { 60 struct frame_head bufhead[2]; 61 62 #ifdef CONFIG_X86_64 63 if ( is_32bit_vcpu(vcpu) ) 64 { 65 COMPAT_HANDLE(char) guest_head = { (full_ptr_t)head }; 66 struct frame_head_32bit bufhead32[2]; 67 /* Also check accessibility of one struct frame_head beyond */ 68 if (!compat_handle_okay(guest_head, sizeof(bufhead32))) 69 return 0; 70 if (__copy_from_compat((char *)bufhead32, guest_head, 71 sizeof(bufhead32))) 72 return 0; 73 bufhead[0].ebp=(struct frame_head *)(full_ptr_t)bufhead32[0].ebp; 74 bufhead[0].ret=bufhead32[0].ret; 75 } 76 else 77 #endif Any advice? Maybe the best option in this case is to avoid the compat* functions and to use the original guest* functions instead. Thanks, Marcus