rogfer01 added a comment.
Firefox build shows a couple of warnings in the sctp library that already gave
warnings with the earlier patches.
That code has the following structure.
#define SCTP_PACKED __attribute__((packed))
#define SCTP_IDENTIFICATION_SIZE 16
// ...
/* state cookie header */
struct sctp_state_cookie { /* this is our definition... */
uint8_t identification[SCTP_IDENTIFICATION_SIZE];/* id of who we are */
struct timeval time_entered; /* the time I built cookie */
// other fields
} SCTP_PACKED;
The warning is triggered by the following code (the other occurence is almost
exact).
net->RTO = sctp_calculate_rto(stcb, asoc, net,
&cookie->time_entered, // ← warning
here!
sctp_align_unsafe_makecopy,
SCTP_RTT_FROM_NON_DATA);
the called function being declared as
uint32_t
sctp_calculate_rto(struct sctp_tcb *stcb,
struct sctp_association *asoc,
struct sctp_nets *net,
struct timeval *told,
int safe, int rtt_from_sack)
{
...
So I think that is a legitimate warning.
But the code is working (assuming this function is ever called that I didn't
check). Checking the code, though, reveals a curious usage of `told`.
/* Copy it out for sparc64 */
if (safe == sctp_align_unsafe_makecopy) {
old = &then;
memcpy(&then, told, sizeof(struct timeval));
} else if (safe == sctp_align_safe_nocopy) {
old = told;
} else {
/* error */
SCTP_PRINTF("Huh, bad rto calc call\n");
return (0);
}
which suggests that the code somehow knows that the pointer is unaligned and
cannot be copied straightforwardly.
We can cast to `void*` and back to the original pointer type.
net->RTO = sctp_calculate_rto(stcb, asoc, net,
(struct
timeval*)(void*)&cookie->time_entered, // note: the cast is because this
pointer is unaligned
sctp_align_unsafe_makecopy,
SCTP_RTT_FROM_NON_DATA);
Which looks a bit ugly to me but clearly pinpoints a problem and can be wrapped
in a macro.
#define UNALIGNED_ADDRESS(x) ((__typeof__(x))(void*)(x))
...
net->RTO = sctp_calculate_rto(stcb, asoc, net,
UNALIGNED_ADDRESS(&cookie->time_entered),
sctp_align_unsafe_makecopy,
SCTP_RTT_FROM_NON_DATA);
What do you think?
http://reviews.llvm.org/D20561
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