Re: [Xen-devel] [PATCH] tools/libxc: Correct XC_DOM_PAGE_SIZE() to return a long long

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 19/11/15 16:50, Wei Liu wrote:
> On Thu, Nov 19, 2015 at 02:45:41PM +0000, Andrew Cooper wrote:
>> c/s abdf3c5b "libxc: create p2m list outside of kernel mapping if supported"
>> introduces a use which Coverity objects to; an int used to mask a uint64_t.
>>
>> The result needs to be signed to allow ~XC_DOM_PAGE_SIZE() to function
> $ git grep XC_DOM_PAGE_SIZE
>
> tools/libxc/include/xc_dom.h:#define XC_DOM_PAGE_SIZE(dom)   (1 << 
> (dom)->arch_hooks
> tools/libxc/include/xc_dom.h:    unsigned int page_size = 
> XC_DOM_PAGE_SIZE(dom);
> tools/libxc/xc_dom_core.c:    unsigned int page_size = XC_DOM_PAGE_SIZE(dom);
> tools/libxc/xc_dom_core.c:    unsigned int page_size = XC_DOM_PAGE_SIZE(dom);
> tools/libxc/xc_dom_core.c:    unsigned int page_size = XC_DOM_PAGE_SIZE(dom);
> tools/libxc/xc_dom_core.c:    unsigned int page_size = XC_DOM_PAGE_SIZE(dom);
> tools/libxc/xc_dom_core.c:    page_size = XC_DOM_PAGE_SIZE(dom);
> tools/libxc/xc_dom_core.c:         (dom->parms.p2m_base & 
> (XC_DOM_PAGE_SIZE(dom) - 1
> tools/libxc/xc_dom_elfloader.c:    elf->dest_size = pages * 
> XC_DOM_PAGE_SIZE(dom);
> tools/libxc/xc_dom_hvmloader.c:    elf->dest_size = pages * 
> XC_DOM_PAGE_SIZE(dom);
> tools/libxc/xc_dom_x86.c:    memset(l3tab, 0, XC_DOM_PAGE_SIZE(dom));
>
> There is no use for ~XC_DOM_PAGE_SIZE.
>
> And what is the possible scenario you want that?

There might not be a current user of this in libxc, but it is a common bug.

From xen/include/asm-x86/page.h

/*                                                                              
                                                                                
                        

 * It is important that the masks are signed quantities. This ensures
that                                                                            
                                  

 * the compiler sign-extends a 32-bit mask to 64 bits if that is
required.                                                                       
                                       

 */
#define PAGE_SIZE           (_AC(1,L) << PAGE_SHIFT)
#define PAGE_MASK           (~(PAGE_SIZE-1))
#define PAGE_FLAG_MASK      (~0)

#define PAGE_ORDER_4K       0
#define PAGE_ORDER_2M       9
#define PAGE_ORDER_1G       18

~Andrew

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