使用vscode+clangd 进行内核代码阅读/开发

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开发环境搭建

由于linux内核代码/头文件最好都放在linux环境下开发测试,在Mac下开发不太方便,记录一下使用vscode + remote ssh 进行远程开发

  1. vscode 安装插件 Remote - SSH 方便连接到linux机器,注意,linux机器不要用docker,自己搭一个虚拟机或者物理机器,方便双机调试
  2. vscode 会自动把 远程服务需要的文件传到linux机器下 所以请配置 ssh 的免密码登录,否则每次打开工程都需要输密码,很麻烦,保证机器至少有100m的空间用来存放vscode远程开发的插件/配置等文件
  3. linux 机器安装 clangd ubuntu下使用 sudo apt install clangd,最好也把clang也安装上,因为代码提示都是靠llvm 编译出的IR来进行AST分析,实现代码提示功能的
  4. linux 机器安装 bear ubuntu下使用 sudo apt install bear 这个是用来自动生成 compile_commands.json 这个文件来配置clangd
  5. vscode 配置 linux机器的clangd,给linux机器装上clangd 插件,配置如下:
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    "clangd.arguments": [
      "--background-index",
      "--completion-style=detailed",
      "--header-insertion=never",
      "-log=info",
      "--pretty",
      "--clang-tidy",
      "--header-insertion=iwyu",
      "--compile-commands-dir=${workspaceFolder}"
    ]
  6. 在${workspaceFolder} 也就是你使用vscode 打开文件夹的目录下新建 .clangd 文件配置详细工作内容,配置如下:
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    CompileFlags: 
      Add:
      [
        "-I/usr/src/linux-headers-5.15.0-46/", # 配置linux源码目录
        "-I./include", # 配置包含目录
        "-DDEBUG", # 配置宏,方便调试模式切换
        "-Wunused-result", # 配置 clang 参数
      ]
      Remove: # 移除 clang 编译时的参数,因为clangd会使用compile_commands.json这个文件的编译参数,但是这个文件是gcc适用的,所以需要移除clang不适用的参数
      [
        "-mpreferred-stack-boundary*",
        "-mindirect-branch=thunk-extern",
        "-mindirect-branch-register",
        "-mfunction-return=thunk-extern",
        "-fno-allow-store-data-races",
        "-fconserve-stack",
        "-mrecord-mcount",
      ]
      Compiler: clang # 注意,内核使用的是gcc来编译代码的,但是此处配置的是使用clang来编译llvm IR进行语法提示,两者是不一样的

    Diagnostics:
      ClangTidy:
        CheckOptions:
          readability-identifier-naming.VariableCase: CamelCase
  7. 配置好clangd之后 还需要使用bear来自动生成内核编译时的参数,因为编译内核都是用Makefile来管理工程的,需要bear配合clangd才能进行自动完成等提示
  8. 在你的内核工程下执行bear -- make此时会生成一个compile_commands.json文件,里面记录了make命令执行过程中用到的所有参数

配置示例:

Makefile:

用来生成内核文件.ko

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export KERNEL_VERSION = $(shell uname -r)
export KERNEL_DIR = /lib/modules/$(KERNEL_VERSION)/build
export KERNEL_TOOL =/usr/src/linux-headers-$(KERNEL_VERSION)/scripts/

obj-m := protect_openat.o # 和源码名称一致
ccflags-y :=-g -DDEBUG # gcc 参数,注意Makefile的参数和clangd是不一样的,clangd只是用来进行语法提示,实际上编译文件还得靠gcc

all:modules

modules:
	@make -C $(KERNEL_DIR) M=$$PWD modules;

.clang-format:

用来格式化/美化代码

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Language:        Cpp
BasedOnStyle:  Google
AccessModifierOffset: -4
AlignAfterOpenBracket: Align
AlignConsecutiveMacros: true
AlignConsecutiveAssignments: true
AlignConsecutiveBitFields: true
AlignConsecutiveDeclarations: true
AlignEscapedNewlines: Right
AlignOperands:   Align
AlignTrailingComments: true
AllowAllArgumentsOnNextLine: true
AllowAllConstructorInitializersOnNextLine: true
AllowAllParametersOfDeclarationOnNextLine: true
AllowShortEnumsOnASingleLine: true
AllowShortBlocksOnASingleLine: Never
AllowShortCaseLabelsOnASingleLine: false
AllowShortFunctionsOnASingleLine: false
AllowShortLambdasOnASingleLine: All
AllowShortIfStatementsOnASingleLine: Never
AllowShortLoopsOnASingleLine: false
AlwaysBreakAfterDefinitionReturnType: None
AlwaysBreakAfterReturnType: None
AlwaysBreakBeforeMultilineStrings: false
AlwaysBreakTemplateDeclarations: MultiLine
BinPackArguments: true
BinPackParameters: true
BraceWrapping:
  AfterCaseLabel:  false
  AfterClass:      false
  AfterControlStatement: Never
  AfterEnum:       false
  AfterFunction:   false
  AfterNamespace:  false
  AfterObjCDeclaration: false
  AfterStruct:     false
  AfterUnion:      false
  AfterExternBlock: false
  BeforeCatch:     false
  BeforeElse:      false
  BeforeLambdaBody: false
  BeforeWhile:     false
  IndentBraces:    false
  SplitEmptyFunction: true
  SplitEmptyRecord: true
  SplitEmptyNamespace: true
BreakBeforeBinaryOperators: None
BreakBeforeBraces: Allman
BreakBeforeInheritanceComma: false
BreakInheritanceList: BeforeColon
BreakBeforeTernaryOperators: true
BreakConstructorInitializersBeforeComma: false
BreakConstructorInitializers: BeforeColon
BreakAfterJavaFieldAnnotations: false
BreakStringLiterals: true
ColumnLimit:     0
CommentPragmas:  '^ IWYU pragma:'
CompactNamespaces: false
ConstructorInitializerAllOnOneLineOrOnePerLine: false
ConstructorInitializerIndentWidth: 4
ContinuationIndentWidth: 4
Cpp11BracedListStyle: true
DeriveLineEnding: true
DerivePointerAlignment: false
DisableFormat:   false
ExperimentalAutoDetectBinPacking: false
FixNamespaceComments: true
ForEachMacros:
  - foreach
  - Q_FOREACH
  - BOOST_FOREACH
IncludeBlocks:   Preserve
IncludeCategories:
  - Regex:           '^"(llvm|llvm-c|clang|clang-c)/'
    Priority:        2
    SortPriority:    0
  - Regex:           '^(<|"(gtest|gmock|isl|json)/)'
    Priority:        3
    SortPriority:    0
  - Regex:           '.*'
    Priority:        1
    SortPriority:    0
IncludeIsMainRegex: '(Test)?$'
IncludeIsMainSourceRegex: ''
IndentCaseLabels: false
IndentCaseBlocks: false
IndentGotoLabels: true
IndentPPDirectives: None
IndentExternBlock: AfterExternBlock
IndentWidth:     4
IndentWrappedFunctionNames: false
InsertTrailingCommas: None
JavaScriptQuotes: Leave
JavaScriptWrapImports: true
KeepEmptyLinesAtTheStartOfBlocks: true
MacroBlockBegin: ''
MacroBlockEnd:   ''
MaxEmptyLinesToKeep: 1
NamespaceIndentation: None
ObjCBinPackProtocolList: Auto
ObjCBlockIndentWidth: 2
ObjCBreakBeforeNestedBlockParam: true
ObjCSpaceAfterProperty: false
ObjCSpaceBeforeProtocolList: true
PenaltyBreakAssignment: 2
PenaltyBreakBeforeFirstCallParameter: 19
PenaltyBreakComment: 300
PenaltyBreakFirstLessLess: 120
PenaltyBreakString: 1000
PenaltyBreakTemplateDeclaration: 10
PenaltyExcessCharacter: 1000000
PenaltyReturnTypeOnItsOwnLine: 60
PointerAlignment: Right
ReflowComments:  true
SortIncludes:    true
SortUsingDeclarations: true
SpaceAfterCStyleCast: false
SpaceAfterLogicalNot: false
SpaceAfterTemplateKeyword: true
SpaceBeforeAssignmentOperators: true
SpaceBeforeCpp11BracedList: false
SpaceBeforeCtorInitializerColon: true
SpaceBeforeInheritanceColon: true
SpaceBeforeParens: ControlStatements
SpaceBeforeRangeBasedForLoopColon: true
SpaceInEmptyBlock: false
SpaceInEmptyParentheses: false
SpacesBeforeTrailingComments: 1
SpacesInAngles:  false
SpacesInConditionalStatement: false
SpacesInContainerLiterals: true
SpacesInCStyleCastParentheses: false
SpacesInParentheses: false
SpacesInSquareBrackets: false
SpaceBeforeSquareBrackets: false
Standard:        Auto
StatementMacros:
  - Q_UNUSED
  - QT_REQUIRE_VERSION
TabWidth:        4
UseCRLF:         false
UseTab:          Never
WhitespaceSensitiveMacros:
  - STRINGIZE
  - PP_STRINGIZE
  - BOOST_PP_STRINGIZE

❕注意事项

  1. 执行bear -- make时,如果你的源码没有变动过,会生成出一个空的compile_commands.json 文件,此时clangd的智能提示会失效,所以在提示失效时,只需要改动一下源码,再重新执行一下bear -- make 即可
  2. clangd配置和Makefile是不一样的,clangd只用于vscode的智能代码提示,头文件的自动查找,Makefile才是用来生成内核ko文件的东西