Re: [PATCH v1.1 03/10] tools/libxg: Drop stale p2m logic from ARM's meminit()

[Julien Grall <julien@xxxxxxx>]

Hi Andrew,

On 12/02/2021 20:01, Andrew Cooper wrote:
> Various version of gcc, when compiling with -Og, complain:
>
>    xg_dom_arm.c: In function 'meminit':
>    xg_dom_arm.c:420:19: error: 'p2m_size' may be used uninitialized in this 
> function [-Werror=maybe-uninitialized]
>      420 |     dom->p2m_size = p2m_size;
>          |     ~~~~~~~~~~~~~~^~~~~~~~~~
>
> This is actually entirely stale code since ee21f10d70^..97e34ad22d which
> removed the 1:1 identity p2m for translated domains.
>
> Drop the write of d->p2m_size, and the p2m_size local variable.  Reposition
> the p2m_size field in struct xc_dom_image and correct some stale
> documentation.
>
> This change really ought to have been part of the original cleanup series.
>
> No actual change to how ARM domains are constructed.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Acked-by: Julien Grall <jgrall@xxxxxxxxxx>

Cheers,

> ---
> CC: Ian Jackson <iwj@xxxxxxxxxxxxxx>
> CC: Wei Liu <wl@xxxxxxx>
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Julien Grall <julien@xxxxxxx>
>
> v2:
>   * Delete stale p2m_size infrastructure.
> ---
>   tools/include/xenguest.h      | 5 ++---
>   tools/libs/guest/xg_dom_arm.c | 5 -----
>   2 files changed, 2 insertions(+), 8 deletions(-)
>
> diff --git a/tools/include/xenguest.h b/tools/include/xenguest.h
> index 775cf34c04..217022b6e7 100644
> --- a/tools/include/xenguest.h
> +++ b/tools/include/xenguest.h
> @@ -145,6 +145,7 @@ struct xc_dom_image {
>        * eventually copied into guest context.
>        */
>       xen_pfn_t *pv_p2m;
> +    xen_pfn_t p2m_size;         /* number of pfns covered by pv_p2m */
>   
>       /* physical memory
>        *
> @@ -154,12 +155,10 @@ struct xc_dom_image {
>        *
>        * An ARM guest has GUEST_RAM_BANKS regions of RAM, with
>        * rambank_size[i] pages in each. The lowest RAM address
> -     * (corresponding to the base of the p2m arrays above) is stored
> -     * in rambase_pfn.
> +     * is stored in rambase_pfn.
>        */
>       xen_pfn_t rambase_pfn;
>       xen_pfn_t total_pages;
> -    xen_pfn_t p2m_size;         /* number of pfns covered by p2m */
>       struct xc_dom_phys *phys_pages;
>   #if defined (__arm__) || defined(__aarch64__)
>       xen_pfn_t rambank_size[GUEST_RAM_BANKS];
> diff --git a/tools/libs/guest/xg_dom_arm.c b/tools/libs/guest/xg_dom_arm.c
> index 94948d2b20..b4c24f15fb 100644
> --- a/tools/libs/guest/xg_dom_arm.c
> +++ b/tools/libs/guest/xg_dom_arm.c
> @@ -373,7 +373,6 @@ static int meminit(struct xc_dom_image *dom)
>       const uint64_t modsize = dtb_size + ramdisk_size;
>       const uint64_t ram128mb = bankbase[0] + (128<<20);
>   
> -    xen_pfn_t p2m_size;
>       uint64_t bank0end;
>   
>       assert(dom->rambase_pfn << XC_PAGE_SHIFT == bankbase[0]);
> @@ -409,16 +408,12 @@ static int meminit(struct xc_dom_image *dom)
>   
>           ramsize -= banksize;
>   
> -        p2m_size = ( bankbase[i] + banksize - bankbase[0] ) >> XC_PAGE_SHIFT;
> -
>           dom->rambank_size[i] = banksize >> XC_PAGE_SHIFT;
>       }
>   
>       assert(dom->rambank_size[0] != 0);
>       assert(ramsize == 0); /* Too much RAM is rejected above */
>   
> -    dom->p2m_size = p2m_size;
> -
>       /* setup initial p2m and allocate guest memory */
>       for ( i = 0; i < GUEST_RAM_BANKS && dom->rambank_size[i]; i++ )
>       {
--
Julien Grall