mirror of
https://github.com/torvalds/linux
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f2644fb44d
Add selftest validating various aspects of statically linking functions:
- no conflicts and correct resolution for name-conflicting static funcs;
- correct resolution of extern functions;
- correct handling of weak functions, both resolution itself and libbpf's
handling of unused weak function that "lost" (it leaves gaps in code with
no ELF symbols);
- correct handling of hidden visibility to turn global function into
"static" for the purpose of BPF verification.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210423181348.1801389-16-andrii@kernel.org
74 lines
2 KiB
C
74 lines
2 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2021 Facebook */
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#include "vmlinux.h"
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_tracing.h>
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/* weak and shared between both files */
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const volatile int my_tid __weak;
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long syscall_id __weak;
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int output_val2;
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int output_ctx2;
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int output_weak2; /* should stay zero */
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/* same "subprog" name in all files, but it's ok because they all are static */
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static __noinline int subprog(int x)
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{
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/* but different formula */
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return x * 2;
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}
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/* Global functions can't be void */
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int set_output_val2(int x)
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{
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output_val2 = 2 * x + 2 * subprog(x);
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return 2 * x;
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}
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/* This function can't be verified as global, as it assumes raw_tp/sys_enter
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* context and accesses syscall id (second argument). So we mark it as
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* __hidden, so that libbpf will mark it as static in the final object file,
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* right before verifying it in the kernel.
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*
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* But we don't mark it as __hidden here, rather at extern site. __hidden is
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* "contaminating" visibility, so it will get propagated from either extern or
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* actual definition (including from the losing __weak definition).
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*/
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void set_output_ctx2(__u64 *ctx)
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{
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output_ctx2 = ctx[1]; /* long id, same as in BPF_PROG below */
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}
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/* this weak instance should lose, because it will be processed second */
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__weak int set_output_weak(int x)
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{
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output_weak2 = x;
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return 2 * x;
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}
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extern int set_output_val1(int x);
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/* here we'll force set_output_ctx1() to be __hidden in the final obj file */
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__hidden extern void set_output_ctx1(__u64 *ctx);
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SEC("raw_tp/sys_enter")
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int BPF_PROG(handler2, struct pt_regs *regs, long id)
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{
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if (my_tid != (u32)bpf_get_current_pid_tgid() || id != syscall_id)
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return 0;
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set_output_val1(2000);
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set_output_ctx1(ctx); /* ctx definition is hidden in BPF_PROG macro */
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/* keep input value the same across both files to avoid dependency on
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* handler call order; differentiate by output_weak1 vs output_weak2.
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*/
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set_output_weak(42);
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return 0;
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}
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char LICENSE[] SEC("license") = "GPL";
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