On 06/21/2018 12:34 AM, no-re...@patchew.org wrote:
Hi,
This series failed docker-mingw@fedora build test. Please find the testing
commands and
their output below. If you have Docker installed, you can probably reproduce it
locally.
/tmp/qemu-test/src/nbd/server.c: In function 'nbd_trip':
/tmp/qemu-test/src/nbd/server.c:1979:19: error: 'end' may be used uninitialized
in this function [-Werror=maybe-uninitialized]
*length = end - offset;
~~~~^~~~~~~~
/tmp/qemu-test/src/nbd/server.c:1940:30: note: 'end' was declared here
uint64_t begin = offset, end;
^~~
This gcc is too stupid to see that end is always initialized:
+/*
+ * Populate @extents from a dirty bitmap. Unless @dont_fragment, the
+ * final extent may exceed the original @length. Store in @length the
+ * byte length encoded (which may be smaller or larger than the
+ * original), and return the number of extents used.
+ */
+static unsigned int bitmap_to_extents(BdrvDirtyBitmap *bitmap, uint64_t offset,
+ uint64_t *length, NBDExtent *extents,
+ unsigned int nb_extents,
+ bool dont_fragment)
+{
+ uint64_t begin = offset, end;
+ uint64_t overall_end = offset + *length;
On input, *length is a non-zero 32-bit number (gcc can't see that)...
+ unsigned int i = 0;
+ BdrvDirtyBitmapIter *it;
+ bool dirty;
+
+ bdrv_dirty_bitmap_lock(bitmap);
+
+ it = bdrv_dirty_iter_new(bitmap);
+ dirty = bdrv_get_dirty_locked(NULL, bitmap, offset);
+
+ while (begin < overall_end && i < nb_extents) {
...so this loop always iterates at least once...
+ if (dirty) {
+ end = bdrv_dirty_bitmap_next_zero(bitmap, begin);
+ } else {
+ bdrv_set_dirty_iter(it, begin);
+ end = bdrv_dirty_iter_next(it);
+ }
...and end is always initialized...
+ if (end == -1) {
+ /* Cap to an aligned value < 4G beyond begin. */
+ end = MIN(bdrv_dirty_bitmap_size(bitmap),
+ begin + 0x100000000ULL -
+ bdrv_dirty_bitmap_granularity(bitmap));
+ }
+ if (dont_fragment && end > overall_end) {
+ end = overall_end;
+ }
+
+ extents[i].length = cpu_to_be32(end - begin);
+ extents[i].flags = cpu_to_be32(dirty ? NBD_STATE_DIRTY : 0);
+ i++;
+ begin = end;
+ dirty = !dirty;
+ }
+
+ bdrv_dirty_iter_free(it);
+
+ bdrv_dirty_bitmap_unlock(bitmap);
+
+ *length = end - offset;
...but gcc didn't know that.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
