* [bpf-next PATCH] samples/bpf: Fix xdp_redirect_map egress devmap prog
@ 2022-07-11 14:04 Jesper Dangaard Brouer
2022-07-12 4:20 ` patchwork-bot+netdevbpf
0 siblings, 1 reply; 2+ messages in thread
From: Jesper Dangaard Brouer @ 2022-07-11 14:04 UTC (permalink / raw)
To: bpf; +Cc: Jesper Dangaard Brouer, netdev, tstellar
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>
---
samples/bpf/xdp_redirect_map.bpf.c | 6 ++++--
samples/bpf/xdp_redirect_map_user.c | 9 +++++++++
2 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/samples/bpf/xdp_redirect_map.bpf.c b/samples/bpf/xdp_redirect_map.bpf.c
index 415bac1758e3..8557c278df77 100644
--- a/samples/bpf/xdp_redirect_map.bpf.c
+++ b/samples/bpf/xdp_redirect_map.bpf.c
@@ -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;
}
diff --git a/samples/bpf/xdp_redirect_map_user.c b/samples/bpf/xdp_redirect_map_user.c
index b6e4fc849577..c889a1394dc1 100644
--- a/samples/bpf/xdp_redirect_map_user.c
+++ b/samples/bpf/xdp_redirect_map_user.c
@@ -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;
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [bpf-next PATCH] samples/bpf: Fix xdp_redirect_map egress devmap prog
2022-07-11 14:04 [bpf-next PATCH] samples/bpf: Fix xdp_redirect_map egress devmap prog Jesper Dangaard Brouer
@ 2022-07-12 4:20 ` patchwork-bot+netdevbpf
0 siblings, 0 replies; 2+ messages in thread
From: patchwork-bot+netdevbpf @ 2022-07-12 4:20 UTC (permalink / raw)
To: Jesper Dangaard Brouer; +Cc: bpf, netdev, tstellar
Hello:
This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:
On Mon, 11 Jul 2022 16:04:22 +0200 you wrote:
> 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.
>
> [...]
Here is the summary with links:
- [bpf-next] samples/bpf: Fix xdp_redirect_map egress devmap prog
https://git.kernel.org/bpf/bpf-next/c/49705c4ab324
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html
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