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linux - 从内核树编译 eBPF C 代码时出错

问题描述

我正在尝试将用 C 编写的 BPF 程序构建到加载它所需的 bpf 字节码中。我用这篇文章试图让我开始：https ://blogs.oracle.com/linux/notes-on-bpf-4

由于库依赖性，我不想使用 BCC。我正在使用 ubuntu 18.04（Linux bpf-ubuntu 4.15.0-1036-gcp #38-Ubuntu SMP Mon Jun 24 13:49:05 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux）

目前我的文件非常简单（并且可能不正确），因为我仍在尝试编译工作：

#include <linux/version.h>
#include <uapi/linux/bpf.h>
#include "bpf_helpers.h"
#include <net/sock.h>

SEC("kprobe/tcp_connect")
int bpf_prog1(struct pt_regs *ctx) {
        struct sock *sk;
        sk = (struct sock*) PT_REGS_PARM1(ctx);
        bpf_trace_printk("%s\n","Got tcp_connect");
}

char _license[] SEC("license") = "GPL";
u32 _version SEC("version") = LINUX_VERSION_CODE;

用于构建和结果的命令是：

clang -nostdinc -isystem `clang -print-file-name=include` \
                -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-address-of-packed-member -Wno-tautological-compare \
                -Wno-unknown-warning-option \
                -I../include -I/usr/src/linux-headers-`uname -r`/include -I/usr/src/linux-headers-`uname -r`/arch/x86/include -I/usr/src/linux-headers-`uname -r`/arch/x86/include/uapi -I/usr/src/linux-headers-`uname -r`/arch/x86/include/generated/uapi -I/usr/src/linux-headers-`uname -r`/include/generated/uapi -I/usr/src/linux-headers-`uname -r`/include/uapi \
                -O2 -emit-llvm -c net_mon_kern.c -o -| llc -march=bpf -filetype=obj -o net_mon_kern.o
In file included from net_mon_kern.c:7:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/net/sock.h:43:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/hardirq.h:5:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/preempt.h:11:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/list.h:9:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/kernel.h:11:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/bitops.h:18:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/bitops.h:514:
/usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/arch_hweight.h:55:42: error: expected ')'
        asm (ALTERNATIVE("call __sw_hweight64", POPCNT64, X86_FEATURE_POPCNT)
                                                ^
/usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/arch_hweight.h:55:6: note: to match this '('
        asm (ALTERNATIVE("call __sw_hweight64", POPCNT64, X86_FEATURE_POPCNT)
            ^
In file included from net_mon_kern.c:7:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/net/sock.h:43:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/hardirq.h:5:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/preempt.h:81:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/preempt.h:7:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/thread_info.h:38:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/thread_info.h:12:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/page.h:14:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/page_32.h:35:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/string.h:19:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/string.h:5:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/string_64.h:6:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/jump_label.h:188:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/atomic.h:5:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/atomic.h:276:
/usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/atomic64_64.h:20:40: error: unknown type name
      'atomic64_t'; did you mean 'atomic_t'?
static inline long atomic64_read(const atomic64_t *v)
                                       ^~~~~~~~~~
                                       atomic_t
/usr/src/linux-headers-4.15.0-1036-gcp/include/linux/types.h:178:3: note: 'atomic_t' declared here
} atomic_t;
  ^

18 more errors relating to atomic64_t...

我不确定如何解决这个问题。我只能假设我包含标题的方式不正确。

标签： linuxclangbpfebpfbcc-bpf

解决方案

TL;DR：尝试linux/kconfig.h在其他包含之前包含。

在我看来，您的命令行的灵感来自内核示例（在 下samples/bpf/），但是您尝试从树中编译，并且修剪了不相关的位。

当您尝试编译代码时，clang 会在您使用-I选项传递的路径中获取所有相关的内核头文件。但是，其中许多标头包含条件定义或包含，具体取决于要构建的内核所请求的配置。例如，include/linux/types.h最终通过 包含<net/sock.h>的 具有以下代码：

#ifdef CONFIG_64BIT
typedef struct {
    long counter;
} atomic64_t;
#endif

但是当你编译时，CONFIG_64BIT从来没有定义过……我让你与你得到的错误信息联系起来:)。

内核样本实际上包括kconfig.h通过LINUXINCLUDEand USERINCLUDE，所以我们必须想办法以某种方式添加它。这显然足以正确设置配置变量并修复编译问题。

我发现以下可能将文件包含在您的案例中：

  • 添加#include <linux/kconfig.h>到您的文件中，然后包含其他内核头文件（例如在第一行）。
  • 或者通过你的命令行添加它：-include linux/kconfig.h，就像内核示例一样（这似乎是最干净的方式）。

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