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推荐一款轻量级 eBPF 前端工具 ply

Sun Jianguo 创作于 2020/10/21

By Jianguo Sun of TinyLab.org Oct 11, 2020

Overview

ply 是 eBPF 的 front-end 前端工具之一,专为 embedded Linux systems 开发,采用 C 语言编写,只需 libc 和内核支持 BPF 就可以运行,不需要外部 kernel 模块,不需要 LLVM,不需要 python。

ply 由瑞典工程师 Tobias Waldekranz 开发,其项目主页是 PLY Light-weight Dynamic Tracer for Linux

使用非常灵活和轻量级,编辑一种类 C 语言的脚本,然后利用内核 eBPF 来收集和探测内核数据,比如打印出内核函数的调用栈,获取内核变量等,是学习内核,进行嵌入式 Linux 系统开发调试的利器!

本文记录 ply 的编译及使用过程,实验例程源码都已上传到 https://github.com/jgsun/buildroot

内核配置

注意: 为顺利使用 ply,内核需要比较新的版本,并且支持 eBPF 和 FTRACE,选择如下配置:

CONFIG_KPROBES=y
CONFIG_HAVE_DYNAMIC_FTRACE=y
CONFIG_HAVE_DYNAMIC_FTRACE_WITH_REGS=y
CONFIG_HAVE_FTRACE_MCOUNT_RECORD=y
CONFIG_FTRACE=y
CONFIG_DYNAMIC_FTRACE=y
CONFIG_BPF=y
CONFIG_BPF_SYSCALL=y

本文实验中所采用内核版本为 Linux v5.8.4。

ply 编译

交叉编译

请提前准备好交叉编译器,大部分 Linux 发行版都提供 ARM64 交叉编译器,直接用包管理工具安装即可,以 Ubuntu 为例:

$ sudo apt-get install gcc-aarch64-linux-gnu

交叉编译步骤举例如下:

$ git clone https://github.com/wkz/ply
$ ./autogen.sh

// 先安装到本地目录下
$ ./configure --host=aarch64-linux-gnu --prefix=~/usr

$ make
$ make install

查看安装目录 ~/usr

~/usr$ tree
.
|-- include
|   `-- ply
|       |-- arch.h
|       |-- buffer.h
|       |-- func.h
|       |-- internal.h
|       |-- ir.h
|       |-- kallsyms.h
|       |-- node.h
|       |-- perf_event.h
|       |-- ply.h
|       |-- printxf.h
|       |-- provider.h
|       |-- sym.h
|       |-- syscall.h
|       |-- type.h
|       `-- utils.h
|-- lib
|   |-- libply.a
|   |-- libply.la
|   |-- libply.so -> libply.so.0.0.0
|   |-- libply.so.0 -> libply.so.0.0.0
|   `-- libply.so.0.0.0
|-- sbin
|   `-- ply
`-- share
    `-- doc
        `-- ply
            |-- COPYING
            `-- README.md
7 directories, 23 files

将 lib 目录的库文件和 sbin 目录的可执行文件 ply 拷贝到 target 板卡的文件系统即可使用,例如:

主机:

~/usr$ scp -P 22 lib/* root@192.168.122.46:/lib
~/usr$ scp -P 22 sbin/ply root@192.168.122.46:~/bin

目标板卡:

root@~/bin# ./ply -v
ply 2.1.1-11-g6aabe5f (linux-version:267277~4.20.13)

root@~/bin# uname -a
Linux qemu-aarch64 5.8.4 #4 SMP Fri Oct 16 11:05:52 CST 2020 aarch64 GNU/Linux

使用 buildroot 编译

ply 项目采用 GNU’s autotools build 系统,非常容易集成到 buildroot,首先在 buildroot 添加 ply package,然后执行 make ply 编译即可。

可以从 buildroot/package/ply 下载,也可以参考下述 patch 修改:

diff --git a/package/Config.in b/package/Config.in
index cb6d8e0e01..7dd278242e 100644
--- a/package/Config.in
+++ b/package/Config.in
@@ -2321,6 +2321,7 @@ menu "System tools"
        source "package/openrc/Config.in"
        source "package/openvmtools/Config.in"
        source "package/pamtester/Config.in"
+       source "package/ply/Config.in"
        source "package/polkit/Config.in"
        source "package/powerpc-utils/Config.in"
        source "package/procps-ng/Config.in"
diff --git a/package/ply/.Config.in.swp b/package/ply/.Config.in.swp
new file mode 100644
index 0000000000..1193f698fb
Binary files /dev/null and b/package/ply/.Config.in.swp differ
diff --git a/package/ply/Config.in b/package/ply/Config.in
new file mode 100644
index 0000000000..258a59b6fd
--- /dev/null
+++ b/package/ply/Config.in
@@ -0,0 +1,11 @@
+config BR2_PACKAGE_PLY
+       bool "ply"
+       depends on BR2_x86_64 || BR2_aarch64 || BR2_arm || BR2_ppc # needs <cpuid.h>
+       depends on BR2_TOOLCHAIN_USES_UCLIBC || BR2_TOOLCHAIN_USES_GLIBC
+       help
+         ply dynamically instruments the running kernel to aggregate and
+         extract user-defined data. It compiles an input program to one or
+         more Linux bpf(2) binaries and attaches them to arbitrary points
+         in the kernel using kprobes and tracepoints.
+
+         https://wkz.github.io/ply/
diff --git a/package/ply/ply.mk b/package/ply/ply.mk
new file mode 100644
index 0000000000..298ea4acf2
--- /dev/null
+++ b/package/ply/ply.mk
@@ -0,0 +1,15 @@
+################################################################################
+#
+# ply
+#
+################################################################################
+
+PLY_VERSION = 2.1.1
+PLY_SITE = https://github.com/wkz/ply/releases/download/$(PLY_VERSION)
+# fetched from Github, with no configure script
+PLY_AUTORECONF = YES
+PLY_DEPENDENCIES = host-bison host-flex
+PLY_LICENSE = GPL-2.0+
+PLY_LICENSE_FILES = COPYING
+
+$(eval $(autotools-package))

ply 示例

网址 root/ply 有部分示例。clone 编译可直接使用:

$ git clone https://github.com/jgsun/buildroot
$ cd buildroot && make qemu_aarch64_virt-fun_defconfig && make
$ qemu-system-aarch64 -M virt \
    -cpu cortex-a57 -nographic -smp 4 -m 512 \
    -kernel output/images/Image \
    -append "root=/dev/ram0 console=ttyAMA0 kmemleak=on loglevel=8" \
    -netdev type=tap,ifname=tap0,id=eth0,script=board/qemu/scripts/qemu-ifup_virbr0,queues=2 \
    -device virtio-net-pci,netdev=eth0,mac='00:00:00:01:00:01',vectors=6,mq=on

打印出内核函数的调用栈

本 ply 示例打印出函数 rtnetlink_rcv 的调用栈:

root@~# cat netlink.ply
#!/usr/bin/env ply

kprobe:rtnetlink_rcv
{
            print(stack);
}

运行 sshnetlink.ply,然后在另外一个终端通过 ssh 登录 qemu aarch64 board,执行 ip addr show dev eth0 命令:

$ ssh -p 22 root@192.168.122.46
root@~# ip addr show dev eth0
3: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether 00:00:00:01:00:01 brd ff:ff:ff:ff:ff:ff
    inet 192.168.122.46/24 brd 192.168.122.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::200:ff:fe01:1/64 scope link
       valid_lft forever preferred_lft forever

netlink.ply 就会打印出 rtnetlink_rcv 的调用栈:

root@~# ./netlink.ply
ply: active
        rtnetlink_rcv
        netlink_sendmsg+408
        ____sys_sendmsg+592
        ___sys_sendmsg+136
        __sys_sendmsg+112
        __arm64_sys_sendmsg+40
        el0_svc_common.constprop.3+144
        do_el0_svc+116
        el0_sync_handler+280
        el0_sync+320

        rtnetlink_rcv
        netlink_sendmsg+408
        ____sys_sendmsg+592
        ___sys_sendmsg+136
        __sys_sendmsg+112
        __arm64_sys_sendmsg+40
        el0_svc_common.constprop.3+144
        do_el0_svc+116
        el0_sync_handler+280
        el0_sync+320

        rtnetlink_rcv
        netlink_sendmsg+408
        __sys_sendto+224
        __arm64_sys_sendto+44
        el0_svc_common.constprop.3+144
        do_el0_svc+116
        el0_sync_handler+280
        el0_sync+320

获取打开文件的进程信息

本 ply 示例打印出发起系统调用 do_sys_open 打开文件的进程名,进程 pid 和文件名(第一个参数):

#!/usr/bin/env ply
kprobe:do_sys_open
{
            printf("%v(%v): %s\n",
               comm, pid, str(arg1));
}

运行结果:

root@~/ply# ./opensnoop.ply
ply: active
dropbear       (  128): /dev/urandom
dropbear       (  128): /proc/timer_list
syslogd        (   60): /var/log/messages
dropbear       (  128): /proc/interrupts
dropbear       (  128): /proc/loadavg
dropbear       (  128): /proc/sys/kernel/random/entropy_avail
dropbear       (  128): /proc/net/netstat
dropbear       (  128): /proc/net/dev
dropbear       (  128): /proc/net/tcp
dropbear       (  128): /proc/net/rt_cache

参考文档



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