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// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2019 Facebook */
#include <linux/bpf.h>
#include "bpf_helpers.h"
#include "bpf_trace_helpers.h"
struct sk_buff {
unsigned int len;
};
static volatile __u64 test_result;
BPF_TRACE_2("fexit/test_pkt_access", test_main,
struct sk_buff *, skb, int, ret)
{
int len;
__builtin_preserve_access_index(({
len = skb->len;
}));
if (len != 74 || ret != 0)
return 0;
test_result = 1;
return 0;
}
static volatile __u64 test_result_subprog1;
BPF_TRACE_2("fexit/test_pkt_access_subprog1", test_subprog1,
struct sk_buff *, skb, int, ret)
{
int len;
__builtin_preserve_access_index(({
len = skb->len;
}));
if (len != 74 || ret != 148)
return 0;
test_result_subprog1 = 1;
return 0;
}
/* Though test_pkt_access_subprog2() is defined in C as:
* static __attribute__ ((noinline))
* int test_pkt_access_subprog2(int val, volatile struct __sk_buff *skb)
* {
* return skb->len * val;
* }
* llvm optimizations remove 'int val' argument and generate BPF assembly:
* r0 = *(u32 *)(r1 + 0)
* w0 <<= 1
* exit
* In such case the verifier falls back to conservative and
* tracing program can access arguments and return value as u64
* instead of accurate types.
*/
struct args_subprog2 {
__u64 args[5];
__u64 ret;
};
static volatile __u64 test_result_subprog2;
SEC("fexit/test_pkt_access_subprog2")
int test_subprog2(struct args_subprog2 *ctx)
{
struct sk_buff *skb = (void *)ctx->args[0];
__u64 ret;
int len;
bpf_probe_read_kernel(&len, sizeof(len),
__builtin_preserve_access_index(&skb->len));
ret = ctx->ret;
/* bpf_prog_load() loads "test_pkt_access.o" with BPF_F_TEST_RND_HI32
* which randomizes upper 32 bits after BPF_ALU32 insns.
* Hence after 'w0 <<= 1' upper bits of $rax are random.
* That is expected and correct. Trim them.
*/
ret = (__u32) ret;
if (len != 74 || ret != 148)
return 0;
test_result_subprog2 = 1;
return 0;
}
char _license[] SEC("license") = "GPL";
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