| Message ID | 20211030164432.1140896-16-jeremy@azazel.net |
|---|---|
| State | Changes Requested |
| Delegated to: | Pablo Neira |
| Headers | show |
| Series | Compiler Warning Fixes | expand |
On Saturday 2021-10-30 18:44, Jeremy Sowden wrote: >`struct ulogd_unixsock_packet_t` is packed, so taking the address of its >`struct iphdr payload` member may yield an unaligned pointer value. That may not be a problem. Dereferencing through a pointer to a packed struct generates very pessimistic code even when there is no padding internally: » cat >>x.cpp <<-EOF struct ethhdr { unsigned long long a, b; } __attribute__((packed)); unsigned long f(const struct ethhdr *p) { return p->b; } EOF » sparc64-linux-gcc -c x.cpp -O2 » objdump -d x.o _Z1fPK6ethhdr: save %sp, -144, %sp stx %i0, [%fp+2039] ldx [%fp+2039], %i0 ldub [%i0+15], %i2 ldub [%i0+14], %i1 sllx %i1, 8, %i1 or %i1, %i2, %i2 ldub [%i0+13], %i3 ...
On 2021-10-30, at 19:42:25 +0200, Jan Engelhardt wrote: > On Saturday 2021-10-30 18:44, Jeremy Sowden wrote: > >`struct ulogd_unixsock_packet_t` is packed, so taking the address of its > >`struct iphdr payload` member may yield an unaligned pointer value. > > That may not be a problem. Dereferencing through a pointer to > a packed struct generates very pessimistic code even when there is no > padding internally: Having taken another look at this, I've adopted different approach to pacify the compiler: the pointer is only actually dereferenced to read one member (`ip->version`), so I shall replace the local pointer variable with an `ip_version` variable instead. J.
diff --git a/input/packet/ulogd_inppkt_UNIXSOCK.c b/input/packet/ulogd_inppkt_UNIXSOCK.c index af2fbeca1f4c..f7611189363c 100644 --- a/input/packet/ulogd_inppkt_UNIXSOCK.c +++ b/input/packet/ulogd_inppkt_UNIXSOCK.c @@ -371,7 +371,7 @@ struct ulogd_unixsock_option_t { static int handle_packet(struct ulogd_pluginstance *upi, struct ulogd_unixsock_packet_t *pkt, uint16_t total_len) { char *data = NULL; - struct iphdr *ip; + struct iphdr ip = pkt->payload; struct ulogd_key *ret = upi->output.keys; uint8_t oob_family; uint16_t payload_len; @@ -387,22 +387,22 @@ static int handle_packet(struct ulogd_pluginstance *upi, struct ulogd_unixsock_p payload_len = ntohs(pkt->payload_length); - ip = &pkt->payload; - if (ip->version == 4) + if (ip.version == 4) oob_family = AF_INET; - else if (ip->version == 6) + else if (ip.version == 6) oob_family = AF_INET6; - else oob_family = 0; + else + oob_family = 0; okey_set_u8(&ret[UNIXSOCK_KEY_OOB_FAMILY], oob_family); - okey_set_ptr(&ret[UNIXSOCK_KEY_RAW_PCKT], ip); + okey_set_ptr(&ret[UNIXSOCK_KEY_RAW_PCKT], &ip); okey_set_u32(&ret[UNIXSOCK_KEY_RAW_PCKTLEN], payload_len); /* options */ if (total_len > payload_len + sizeof(uint16_t)) { /* option starts at the next aligned address after the payload */ new_offset = USOCK_ALIGN(payload_len); - options_start = (void*)ip + new_offset; + options_start = (char *) &ip + new_offset; data = options_start; total_len -= (options_start - (char*)pkt); @@ -460,7 +460,7 @@ static int handle_packet(struct ulogd_pluginstance *upi, struct ulogd_unixsock_p "ulogd2: unknown option %d\n", option_number); break; - }; + } } } @@ -674,7 +674,7 @@ static int unixsock_instance_read_cb(int fd, unsigned int what, void *param) } /* handle_packet has shifted data in buffer */ - }; + } return 0; }
`struct ulogd_unixsock_packet_t` is packed, so taking the address of its `struct iphdr payload` member may yield an unaligned pointer value. Copy it to a local variable instead. Remove a couple of stray semicolons. Signed-off-by: Jeremy Sowden <jeremy@azazel.net> --- input/packet/ulogd_inppkt_UNIXSOCK.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-)