Compile Linux 2.6.18 kernel. Warns that idx may be uninitialized in
fs/bio.c:bio_alloc_bioset(), but it clearly *is* being initialized
by bvec_alloc_bs.
The kernel team will not allow us to pre-initialize these, as it is
a gcc bug. On the other hand, we're drowned in invalid warnings, so
can't see any real problems. Older versions of gcc (3.x) did not
have this problem.
struct bio *bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set *bs)
{
struct bio *bio = mempool_alloc(bs->bio_pool, gfp_mask);
if (likely(bio)) {
struct bio_vec *bvl = NULL;
bio_init(bio);
if (likely(nr_iovecs)) {
unsigned long idx;
bvl = bvec_alloc_bs(gfp_mask, nr_iovecs, &idx, bs);
if (unlikely(!bvl)) {
mempool_free(bio, bs->bio_pool);
bio = NULL;
goto out;
}
bio->bi_flags |= idx << BIO_POOL_OFFSET;
bio->bi_max_vecs = bvec_slabs[idx].nr_vecs;
}
bio->bi_io_vec = bvl;
}
out:
return bio;
}
static inline struct bio_vec *bvec_alloc_bs(gfp_t gfp_mask, int nr, unsigned
long *idx, struct bio_set *bs)
{
struct bio_vec *bvl;
struct biovec_slab *bp;
/*
* see comment near bvec_array define!
*/
switch (nr) {
case 1 : *idx = 0; break;
case 2 ... 4: *idx = 1; break;
case 5 ... 16: *idx = 2; break;
case 17 ... 64: *idx = 3; break;
case 65 ... 128: *idx = 4; break;
case 129 ... BIO_MAX_PAGES: *idx = 5; break;
default:
return NULL;
}
/*
* idx now points to the pool we want to allocate from
*/
bp = bvec_slabs + *idx;
bvl = mempool_alloc(bs->bvec_pools[*idx], gfp_mask);
if (bvl)
memset(bvl, 0, bp->nr_vecs * sizeof(struct bio_vec));
return bvl;
}
--
Summary: Gcc gives invalid warning about unitialized variable
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: mbligh at mbligh dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29574
