Messages in this thread | | | Date | Tue, 18 Mar 2014 10:37:58 -0700 | From | Behan Webster <> | Subject | Re: [PATCH v2] net: netfilter: LLVMLinux: vlais-netfilter |
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On 03/18/14 08:24, David Laight wrote: > From: Behan Webster >> On 03/18/14 02:41, David Laight wrote: >>> From: behanw@converseincode.com >>>> From: Mark Charlebois <charlebm@gmail.com> >>>> >>>> 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@converseincode.com
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