my program is too huge so I start with simple example using xdp1_kern.c
I tried adding an ethernet header as local variable:
--- a/samples/bpf/xdp1_kern.c
+++ b/samples/bpf/xdp1_kern.c
@@ -51,10 +51,19 @@ int xdp_prog1(struct xdp_md *ctx)
u64 nh_off;
u32 ipproto;
+ struct ethhdr myeth;
+
nh_off = sizeof(*eth);
if (data + nh_off > data_end)
return rc;
+ myeth.h_dest[0] = eth->h_source[0];
+ myeth.h_dest[1] = eth->h_source[1];
+ myeth.h_dest[2] = eth->h_source[2];
+ myeth.h_dest[3] = eth->h_source[3];
+ myeth.h_dest[4] = eth->h_source[4];
+ myeth.h_dest[5] = eth->h_source[5];
+
h_proto = eth->h_proto;
if (h_proto == htons(ETH_P_8021Q) || h_proto == htons(ETH_P_8021AD)) {
@@ -87,6 +96,7 @@ int xdp_prog1(struct xdp_md *ctx)
if (value)
*value += 1;
+ memcpy(eth, &myeth, sizeof(myeth));
return rc;
}
---------
Then using llvm-objdump, it shows:
; myeth.h_dest[5] = eth->h_source[5];
24: r4 = *(u8 *)(r1 + 11)
; myeth.h_dest[4] = eth->h_source[4];
25: r5 = *(u8 *)(r1 + 10)
; myeth.h_dest[3] = eth->h_source[3];
26: r0 = *(u8 *)(r1 + 9)
; myeth.h_dest[2] = eth->h_source[2];
27: r6 = *(u8 *)(r1 + 8)
; myeth.h_dest[1] = eth->h_source[1];
28: r7 = *(u8 *)(r1 + 7)
; myeth.h_dest[0] = eth->h_source[0];
29: r8 = *(u8 *)(r1 + 6)
30: r1 += 6
; if (h_proto == htons(ETH_P_8021Q) || h_proto == htons(ETH_P_8021AD)) {
31: *(u64 *)(r10 - 72) = r1
32: *(u64 *)(r10 - 80) = r2
33: *(u64 *)(r10 - 88) = r3
34: *(u64 *)(r10 - 96) = r4
35: *(u64 *)(r10 - 104) = r5
36: *(u64 *)(r10 - 112) = r0
37: *(u64 *)(r10 - 120) = r6
38: *(u64 *)(r10 - 128) = r7
39: *(u64 *)(r10 - 136) = r8
----
by observing that it's always 8 byte offset, r10 - 136, 128, 120, 112....
the local variable myeth.h_dest[6] seems to take 6 * 8 = 48 Byte on stack.
and my ethernet header will take 8 * (6+6) + 2 = 50 Byte
Considering my other header structure definitions, I think it's the
reason I use more than 512 byte stack memory.
--William
On Thu, Feb 9, 2017 at 9:48 AM, William Tu <[email protected]> wrote:
> On Thu, Feb 9, 2017 at 8:59 AM, Alexei Starovoitov
> <[email protected]> wrote:
>> On Thu, Feb 9, 2017 at 8:43 AM, William Tu via iovisor-dev
>> <[email protected]> wrote:
>>>
>>> $(CLANG) \
>>> -D__KERNEL__ -D__ASM_SYSREG_H -Wno-unused-value -Wno-pointer-sign \
>>> -Wno-compare-distinct-pointer-types \
>>> -Wno-gnu-variable-sized-type-not-at-end \
>>> -Wno-tautological-compare \
>>> -O2 -emit-llvm -g -c $< -o -| $(LLC) -O0 -march=bpf -filetype=obj
>>> -o $@
>>
>> -O0 ?!
>> yeah. that should not work.
>> always use -O2 for llvm or don't specify it at all and keep -O2 for clang.
>
> oh, the code I shared doesn't specify it at all.
> "-O0" is just something I'm playing around to see any diff.
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