Avoid using a variable length array.
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---
Notes:
Was suggested by Peter here:
<CAFEAcA88+A2oCkQnxKDEdpmfCZSmPzWMBg01wDDV68bMZoY5Jg@mail.gmail.com>
"should we try to stop using variable length arrays?"
hw/i386/xen/xen-hvm.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/hw/i386/xen/xen-hvm.c b/hw/i386/xen/xen-hvm.c
index 725f9c2278..10d73b55b4 100644
--- a/hw/i386/xen/xen-hvm.c
+++ b/hw/i386/xen/xen-hvm.c
@@ -615,7 +615,8 @@ static void xen_sync_dirty_bitmap(XenIOState *state,
{
hwaddr npages = size >> TARGET_PAGE_BITS;
const int width = sizeof(unsigned long) * 8;
- unsigned long bitmap[DIV_ROUND_UP(npages, width)];
+ unsigned long *bitmap = NULL;
+ size_t bitmap_size = DIV_ROUND_UP(npages, width);
int rc, i, j;
const XenPhysmap *physmap = NULL;
@@ -632,6 +633,8 @@ static void xen_sync_dirty_bitmap(XenIOState *state,
return;
}
+ bitmap = g_new0(unsigned long, bitmap_size);
+
rc = xen_track_dirty_vram(xen_domid, start_addr >> TARGET_PAGE_BITS,
npages, bitmap);
if (rc < 0) {
@@ -644,10 +647,10 @@ static void xen_sync_dirty_bitmap(XenIOState *state,
", 0x" TARGET_FMT_plx "): %s\n",
start_addr, start_addr + size, strerror(errno));
}
- return;
+ goto out;
}
- for (i = 0; i < ARRAY_SIZE(bitmap); i++) {
+ for (i = 0; i < bitmap_size; i++) {
unsigned long map = bitmap[i];
while (map != 0) {
j = ctzl(map);
@@ -657,6 +660,8 @@ static void xen_sync_dirty_bitmap(XenIOState *state,
TARGET_PAGE_SIZE);
};
}
+out:
+ g_free(bitmap);
}
static void xen_log_start(MemoryListener *listener,
--
Anthony PERARD
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel> -----Original Message-----
> From: Anthony PERARD [mailto:anthony.perard@citrix.com]
> Sent: 17 June 2019 16:41
> To: qemu-devel@nongnu.org
> Cc: xen-devel@lists.xenproject.org; Anthony Perard <anthony.perard@citrix.com>; Stefano Stabellini
> <sstabellini@kernel.org>; Paul Durrant <Paul.Durrant@citrix.com>
> Subject: [PATCH 4/4] xen: Avoid VLA
>
> Avoid using a variable length array.
>
> Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
> ---
>
> Notes:
> Was suggested by Peter here:
> <CAFEAcA88+A2oCkQnxKDEdpmfCZSmPzWMBg01wDDV68bMZoY5Jg@mail.gmail.com>
> "should we try to stop using variable length arrays?"
>
> hw/i386/xen/xen-hvm.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/hw/i386/xen/xen-hvm.c b/hw/i386/xen/xen-hvm.c
> index 725f9c2278..10d73b55b4 100644
> --- a/hw/i386/xen/xen-hvm.c
> +++ b/hw/i386/xen/xen-hvm.c
> @@ -615,7 +615,8 @@ static void xen_sync_dirty_bitmap(XenIOState *state,
> {
> hwaddr npages = size >> TARGET_PAGE_BITS;
> const int width = sizeof(unsigned long) * 8;
> - unsigned long bitmap[DIV_ROUND_UP(npages, width)];
> + unsigned long *bitmap = NULL;
> + size_t bitmap_size = DIV_ROUND_UP(npages, width);
> int rc, i, j;
> const XenPhysmap *physmap = NULL;
>
> @@ -632,6 +633,8 @@ static void xen_sync_dirty_bitmap(XenIOState *state,
> return;
> }
>
> + bitmap = g_new0(unsigned long, bitmap_size);
> +
How hot is this function? It looks (unsurprisingly) like the section size determines the map size so I wonder whether it can instead be allocated once when the section is added?
Paul
> rc = xen_track_dirty_vram(xen_domid, start_addr >> TARGET_PAGE_BITS,
> npages, bitmap);
> if (rc < 0) {
> @@ -644,10 +647,10 @@ static void xen_sync_dirty_bitmap(XenIOState *state,
> ", 0x" TARGET_FMT_plx "): %s\n",
> start_addr, start_addr + size, strerror(errno));
> }
> - return;
> + goto out;
> }
>
> - for (i = 0; i < ARRAY_SIZE(bitmap); i++) {
> + for (i = 0; i < bitmap_size; i++) {
> unsigned long map = bitmap[i];
> while (map != 0) {
> j = ctzl(map);
> @@ -657,6 +660,8 @@ static void xen_sync_dirty_bitmap(XenIOState *state,
> TARGET_PAGE_SIZE);
> };
> }
> +out:
> + g_free(bitmap);
> }
>
> static void xen_log_start(MemoryListener *listener,
> --
> Anthony PERARD
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
On Mon, Jun 17, 2019 at 05:39:09PM +0100, Paul Durrant wrote: > > @@ -632,6 +633,8 @@ static void xen_sync_dirty_bitmap(XenIOState *state, > > return; > > } > > > > + bitmap = g_new0(unsigned long, bitmap_size); > > + > > How hot is this function? It looks (unsurprisingly) like the section > size determines the map size so I wonder whether it can instead be > allocated once when the section is added? I think we can store the bitmap buffer into the `state' where `log_for_dirtybit' is already present, and free the bitmap when `log_for_dirtybit' is cleared. Thanks, -- Anthony PERARD _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
> -----Original Message----- > From: Anthony PERARD [mailto:anthony.perard@citrix.com] > Sent: 17 June 2019 18:37 > To: Paul Durrant <Paul.Durrant@citrix.com> > Cc: qemu-devel@nongnu.org; xen-devel@lists.xenproject.org; Stefano Stabellini <sstabellini@kernel.org> > Subject: Re: [PATCH 4/4] xen: Avoid VLA > > On Mon, Jun 17, 2019 at 05:39:09PM +0100, Paul Durrant wrote: > > > @@ -632,6 +633,8 @@ static void xen_sync_dirty_bitmap(XenIOState *state, > > > return; > > > } > > > > > > + bitmap = g_new0(unsigned long, bitmap_size); > > > + > > > > How hot is this function? It looks (unsurprisingly) like the section > > size determines the map size so I wonder whether it can instead be > > allocated once when the section is added? > > I think we can store the bitmap buffer into the `state' where > `log_for_dirtybit' is already present, and free the bitmap when > `log_for_dirtybit' is cleared. That sounds better :-) Cheers, Paul > > Thanks, > > -- > Anthony PERARD
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