Commit 49705c4a authored by Jesper Dangaard Brouer's avatar Jesper Dangaard Brouer Committed by Andrii Nakryiko
Browse files

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: default avatarJesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/165754826292.575614.5636444052787717159.stgit@firesoul
parent efc9909f

samples/bpf/xdp_redirect_map.bpf.c

+4 −2
Original line number Diff line number Diff line
@@ -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;

}

samples/bpf/xdp_redirect_map_user.c

+9 −0
Original line number Diff line number Diff line
@@ -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;