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samples/bpf: Fix xdp_redirect_map egress devmap prog 

LLVM compiler optimized out the memcpy in xdp_redirect_map_egress,
which caused the Ethernet source MAC-addr to always be zero
when enabling the devmap egress prog via cmdline --load-egress.

Issue observed with LLVM version 14.0.0
 - Shipped with Fedora 36 on target: x86_64-redhat-linux-gnu.

In verbose mode print the source MAC-addr in case xdp_devmap_attached
mode is used.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/165754826292.575614.5636444052787717159.stgit@firesoul
This commit is contained in:
Jesper Dangaard Brouer 2022-07-11 16:04:22 +02:00 committed by Andrii Nakryiko
parent efc9909fdc
commit 49705c4ab3
2 changed files with 13 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
samples/bpf/xdp_redirect_map.bpf.c
View File

@ -33,7 +33,7 @@ struct {
} tx_port_native SEC(".maps");
/* store egress interface mac address */
const volatile char tx_mac_addr[ETH_ALEN];
const volatile __u8 tx_mac_addr[ETH_ALEN];
static __always_inline int xdp_redirect_map(struct xdp_md *ctx, void *redirect_map)
{
@ -73,6 +73,7 @@ int xdp_redirect_map_egress(struct xdp_md *ctx)
{
void *data_end = (void *)(long)ctx->data_end;
void *data = (void *)(long)ctx->data;
u8 *mac_addr = (u8 *) tx_mac_addr;
struct ethhdr *eth = data;
u64 nh_off;
@ -80,7 +81,8 @@ int xdp_redirect_map_egress(struct xdp_md *ctx)
if (data + nh_off > data_end)
return XDP_DROP;
__builtin_memcpy(eth->h_source, (const char *)tx_mac_addr, ETH_ALEN);
barrier_var(mac_addr); /* prevent optimizing out memcpy */
__builtin_memcpy(eth->h_source, mac_addr, ETH_ALEN);
return XDP_PASS;
}

9
samples/bpf/xdp_redirect_map_user.c
View File

@ -40,6 +40,8 @@ static const struct option long_options[] = {
{}
};
static int verbose = 0;
int main(int argc, char **argv)
{
struct bpf_devmap_val devmap_val = {};
@ -79,6 +81,7 @@ int main(int argc, char **argv)
break;
case 'v':
sample_switch_mode();
verbose = 1;
break;
case 's':
mask |= SAMPLE_REDIRECT_MAP_CNT;
@ -134,6 +137,12 @@ int main(int argc, char **argv)
ret = EXIT_FAIL;
goto end_destroy;
}
if (verbose)
printf("Egress ifindex:%d using src MAC %02x:%02x:%02x:%02x:%02x:%02x\n",
ifindex_out,
skel->rodata->tx_mac_addr[0], skel->rodata->tx_mac_addr[1],
skel->rodata->tx_mac_addr[2], skel->rodata->tx_mac_addr[3],
skel->rodata->tx_mac_addr[4], skel->rodata->tx_mac_addr[5]);
}
skel->rodata->from_match[0] = ifindex_in;