On 03/18/14 08:24, David Laight wrote:
From: Behan Webster
On 03/18/14 02:41, David Laight wrote:
From: behanw@xxxxxxxxxxxxxxxxxx
From: Mark Charlebois <charlebm@xxxxxxxxx>
Replaced non-standard C use of Variable Length Arrays In Structs (VLAIS) in
xt_repldata.h with a C99 compliant flexible array member and then calculated
offsets to the other struct members. These other members aren't referenced by
name in this code, however this patch maintains the same memory layout and
padding as was previously accomplished using VLAIS.
Had the original structure been ordered differently, with the entries VLA at
the end, then it could have been a flexible member, and this patch would have
been a lot simpler. However since the data stored in this structure is
ultimately exported to userspace, the order of this structure can't be changed.
Why not just remove the last element and allocate space for it after the
structure?
Because that would still be employing VLAIS to solve the problem. The
last element may be a zero-length array (a flexible member), not a VLA.
Sadly both the last 2 elements in the struct need to be manually
calculated, which is what we've done.
So make the last element a 'flexible member' and then work out where
the final field goes.
Something like:
struct p {
struct a a;
struct b b[];
} p = malloc(sizeof *p + n * sizeof (struct b) + alignof (struct c)
+ sizeof (struct c);
struct c *c = (void *)&p->b[n] + (-offsetof(struct p, b[n]) & (alignof(struct c) - 1);
Oh, I see. Will fix.
Thanks!
Behan
--
Behan Webster
behanw@xxxxxxxxxxxxxxxxxx
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