53f8dd434b
Similarly to a0d7da26ce86 ("libbpf: Fix call relocation offset calculation
bug"), relocations against global variables need to take into account
referenced symbol's st_value, which holds offset into a corresponding data
section (and, subsequently, offset into internal backing map). For static
variables this offset is always zero and data offset is completely described
by respective instruction's imm field.
Convert a bunch of selftests to global variables. Previously they were relying
on `static volatile` trick to ensure Clang doesn't inline static variables,
which with global variables is not necessary anymore.
Fixes: 393cdfbee809 ("libbpf: Support initialized global variables")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20191127200651.1381348-1-andriin@fb.com
83 lines
1.9 KiB
C
83 lines
1.9 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2019 Facebook */
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#include <linux/bpf.h>
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#include "bpf_helpers.h"
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#include "bpf_trace_helpers.h"
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struct sk_buff {
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unsigned int len;
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};
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__u64 test_result = 0;
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BPF_TRACE_2("fexit/test_pkt_access", test_main,
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struct sk_buff *, skb, int, ret)
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{
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int len;
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__builtin_preserve_access_index(({
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len = skb->len;
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}));
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if (len != 74 || ret != 0)
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return 0;
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test_result = 1;
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return 0;
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}
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__u64 test_result_subprog1 = 0;
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BPF_TRACE_2("fexit/test_pkt_access_subprog1", test_subprog1,
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struct sk_buff *, skb, int, ret)
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{
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int len;
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__builtin_preserve_access_index(({
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len = skb->len;
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}));
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if (len != 74 || ret != 148)
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return 0;
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test_result_subprog1 = 1;
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return 0;
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}
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/* Though test_pkt_access_subprog2() is defined in C as:
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* static __attribute__ ((noinline))
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* int test_pkt_access_subprog2(int val, volatile struct __sk_buff *skb)
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* {
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* return skb->len * val;
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* }
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* llvm optimizations remove 'int val' argument and generate BPF assembly:
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* r0 = *(u32 *)(r1 + 0)
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* w0 <<= 1
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* exit
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* In such case the verifier falls back to conservative and
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* tracing program can access arguments and return value as u64
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* instead of accurate types.
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*/
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struct args_subprog2 {
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__u64 args[5];
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__u64 ret;
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};
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__u64 test_result_subprog2 = 0;
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SEC("fexit/test_pkt_access_subprog2")
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int test_subprog2(struct args_subprog2 *ctx)
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{
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struct sk_buff *skb = (void *)ctx->args[0];
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__u64 ret;
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int len;
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bpf_probe_read_kernel(&len, sizeof(len),
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__builtin_preserve_access_index(&skb->len));
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ret = ctx->ret;
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/* bpf_prog_load() loads "test_pkt_access.o" with BPF_F_TEST_RND_HI32
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* which randomizes upper 32 bits after BPF_ALU32 insns.
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* Hence after 'w0 <<= 1' upper bits of $rax are random.
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* That is expected and correct. Trim them.
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*/
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ret = (__u32) ret;
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if (len != 74 || ret != 148)
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return 0;
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test_result_subprog2 = 1;
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return 0;
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}
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char _license[] SEC("license") = "GPL";
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