Linux内核调试——dynamic_debug

发表于 分类于 阅读次数： 阅读次数： 本文字数： 3.7k 阅读时长 ≈ 3 分钟

dynamic debug (dyndbg)是内核提供的一个调试功能，允许动态的开关内核打印输出，包含的API：pr_debug()、dev_dbg()、print_hex_dump_debug()、print_hex_dump_bytes()等。
dynamic debug通过设置/dynamic_debug/control文件来控制内核输出，有多种匹配的条件：文件名，函数名，行号，模块名和输出字符的格式；

开启配置

1
2
CONFIG_DEBUG_FS=y
CONFIG_DYNAMIC_DEBUG=y

sys文件系统：

1
2
# ls /sys/kernel/debug/dynamic_debug/
control

查询所有开启了dynamic debug选项的文件；

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
# cat /sys/kernel/debug/dynamic_debug/control
# filename:lineno [module]function flags format
init/main.c:857 [main]initcall_blacklisted =p "initcall %s blacklisted\012"
init/main.c:818 [main]initcall_blacklist =p "blacklisting initcall %s\012"
init/initramfs.c:477 [initramfs]unpack_to_rootfs =_ "Detected %s compressed data\012"
arch/arm64/kernel/setup.c:122 [setup]smp_build_mpidr_hash =_ "mask of set bits %#llx\012"
arch/arm64/kernel/setup.c:156 [setup]smp_build_mpidr_hash =_ "MPIDR hash: aff0[%u] aff1[%u] aff2[%u] aff3[%u] mask[%#llx] bits[%u]\012"
arch/arm64/kernel/traps.c:90 [traps]dump_backtrace =_ "%s(regs = %p tsk = %p)\012"
arch/arm64/kernel/smp.c:667 [smp]of_parse_and_init_cpus =_ "cpu logical map 0x%llx\012"
arch/arm64/kernel/topology.c:56 [topology]store_cpu_topology =_ "CPU%u: cluster %d core %d thread %d mpidr %#016llx\012"
arch/arm64/kernel/armv8_deprecated.c:401 [armv8_deprecated]swp_handler =_ "addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\012"
arch/arm64/kernel/armv8_deprecated.c:408 [armv8_deprecated]swp_handler =_ "SWP{B} emulation: access to 0x%08x not allowed!\012"
arch/arm64/kernel/armv8_deprecated.c:326 [armv8_deprecated]emulate_swpX =_ "SWP instruction on unaligned pointer!\012"
arch/arm64/kernel/armv8_deprecated.c:432 [armv8_deprecated]swp_handler =_ "SWP{B} emulation: access caused memory abort!\012"
kernel/params.c:177 [params]parse_args =_ "doing %s, parsing ARGS: '%s'\012"
kernel/params.c:139 [params]parse_one =_ "handling %s with %p\012"
kernel/params.c:152 [params]parse_one =_ "doing %s: %s='%s'\012"
kernel/params.c:156 [params]parse_one =_ "Unknown argument '%s'\012"
...

control文件的语法格式

1
command ::= match-spec* flags-spec

匹配的关键字：

1
2
3
4
5
6
7
8
9
10
11
12
13
match-spec ::= 'func' string |
               'file' string |
               'module' string |
               'format' string |
               'class' string |
               'line' line-range

line-range ::= lineno |
               '-'lineno |
               lineno'-' |
               lineno'-'lineno

lineno ::= unsigned-int

flags-spec包括一个更改操作，后跟一个或多个标志字符。更改操作是以下字符之一：

1
2
3
-    remove the given flags
+    add the given flags
=    set the flags to the given flags

flags包括：

1
2
3
4
5
6
7
8
p    enables the pr_debug() callsite.
_    enables no flags.

Decorator flags add to the message-prefix, in order:
t    Include thread ID, or <intr>
m    Include module name
f    Include the function name
l    Include line number

组合参数就有：

  • +mp: 输出打打印包含模块名
  • +mfp： 输出打印包含模块名、函数名
  • +mflp： 输出打印包含模块名、函数名、行号
  • +mflp： 输出打印包含模块名、函数名、行号、线程号

使用方法

内核实现：lib/dynamic_debug.c

1
2
3
4
5
6
7
8
9
10
Parse words[] as a ddebug query specification, which is a series
of (keyword, value) pairs chosen from these possibilities:

func <function-name>
file <full-pathname>
file <base-filename>
module <module-name>
format <escaped-string-to-find-in-format>
line <lineno>
line <first-lineno>-<last-lineno> // where either may be empty

开启某个文件中的pr_debug或dev_dbg

输出打印

开启后内核日志将输出到dmesg,串口不会输出。也可以在/var/log/messages中查看。

  • 指定调试文件

    1
    echo "file mm/cma.c +p" > /sys/kernel/debug/dynamic_debug/control
    1
    echo "file mm/cma.c +mfplt" > /sys/kernel/debug/dynamic_debug/control

  • 指定调试模块

    1
    echo "module cma +p" > /sys/kernel/debug/dynamic_debug/control

关闭打印

1
echo "file mm/cma.c -p" > /sys/kernel/debug/dynamic_debug/control
1
echo "module cma -p" > /sys/kernel/debug/dynamic_debug/control

参考

  • 内核文档——Dynamic debug