pp-trace User’s Manual — Extra Clang Tools 20.1.8 documentation

# Extra Clang Tools 20.1.8 documentation

## pp-trace User’s Manual

pp-trace is a standalone tool that traces preprocessor activity. It’s also used as a test of Clang’s PPCallbacks interface. It runs a given source file through the Clang preprocessor, displaying selected information from callback functions overridden in a PPCallbacks derivation. The output is in a high-level YAML format, described in pp-trace Output Format.

## pp-trace Usage

### Command Line Format

`pp-trace [<pp-trace-options>] <source-file> [-- <front-end-options>]`

`<pp-trace-options>` is a place-holder for options specific to pp-trace, which are described below in Command Line Options.

`<source-file>` specifies the source file to run through the preprocessor.

`<front-end-options>` is a place-holder for regular Clang Compiler Options, which must follow the <source-file>.

### Command Line Options

-callbacks <comma-separated-globs>

  This option specifies a comma-separated list of globs describing the list of callbacks that should be traced. Globs are processed in order of appearance. Positive globs add matched callbacks to the set, negative globs (those with the ‘-’ prefix) remove callacks from the set.

  - FileChanged

  - FileSkipped

  - InclusionDirective

  - moduleImport

  - EndOfMainFile

  - Ident

  - PragmaDirective

  - PragmaComment

  - PragmaDetectMismatch

  - PragmaDebug

  - PragmaMessage

  - PragmaDiagnosticPush

  - PragmaDiagnosticPop

  - PragmaDiagnostic

  - PragmaOpenCLExtension

  - PragmaWarning

  - PragmaWarningPush

  - PragmaWarningPop

  - MacroExpands

  - MacroDefined

  - MacroUndefined

  - Defined

  - SourceRangeSkipped

  - If

  - Elif

  - Ifdef

  - Ifndef

  - Else

  - Endif

-output <output-file>

  By default, pp-trace outputs the trace information to stdout. Use this option to output the trace information to a file.

## pp-trace Output Format

The pp-trace output is formatted as YAML. See https://yaml.org/ for general YAML information. It’s arranged as a sequence of information about the callback call, including the callback name and argument information, for example::

    ---
    - Callback: Name
      Argument1: Value1
      Argument2: Value2
    (etc.)
    ...

With real data::

    ---
    - Callback: FileChanged
      Loc: "c:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-include.cpp:1:1"
      Reason: EnterFile
      FileType: C_User
      PrevFID: (invalid)
      (etc.)
    - Callback: FileChanged
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-include.cpp:5:1"
      Reason: ExitFile
      FileType: C_User
      PrevFID: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/Input/Level1B.h"
    - Callback: EndOfMainFile
    ...

In all but one case (MacroDirective) the “Argument” scalars have the same name as the argument in the corresponding PPCallbacks callback function.

### Callback Details

The following sections describe the purpose and output format for each callback.

Click on the callback name in the section heading to see the Doxygen documentation for the callback.

The argument descriptions table describes the callback argument information displayed.

The Argument Name field in most (but not all) cases is the same name as the callback function parameter.

The Argument Value Syntax field describes the values that will be displayed for the argument value. It uses an ad hoc representation that mixes literal and symbolic representations. Enumeration member symbols are shown as the actual enum member in a (member1|member2|…) form. A name in parentheses can either represent a place holder for the described value, or confusingly, it might be a literal, such as (null), for a null pointer. Locations are shown as quoted only to avoid confusing the documentation generator.

The Clang C++ Type field is the type from the callback function declaration.

The description describes the argument or what is displayed for it.

Note that in some cases, such as when a structure pointer is an argument value, only some key member or members are shown to represent the value, instead of trying to display all members of the structure.

#### FileChanged Callback

FileChanged is called when the preprocessor enters or exits a file, both the top level file being compiled, as well as any #include directives. It will also be called as a result of a system header pragma or in internal renaming of a file.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Reason | (EnterFile|ExitFile|SystemHeaderPragma|RenameFile) | PPCallbacks::FileChangeReason | Reason for change.
FileType | (C_User|C_System|C_ExternCSystem) | SrcMgr::CharacteristicKind | Include type.
PrevFID | ((file)|(invalid)) | FileID | Previous file, if any.

Example::

    - Callback: FileChanged
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-include.cpp:1:1"
      Reason: EnterFile
      FileType: C_User
      PrevFID: (invalid)

#### FileSkipped Callback

FileSkipped is called when a source file is skipped as the result of header guard optimization.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
ParentFile | (“(file)” or (null)) | const FileEntry | The file that #included the skipped file.
FilenameTok | (token) | const Token | The token in ParentFile that indicates the skipped file.
FileType | (C_User|C_System|C_ExternCSystem) | SrcMgr::CharacteristicKind | The file type.

Example::

    - Callback: FileSkipped
      ParentFile: "/path/filename.h"
      FilenameTok: "filename.h"
      FileType: C_User

#### InclusionDirective Callback

InclusionDirective is called when an inclusion directive of any kind (#include</code>, #import</code>, etc.) has been processed, regardless of whether the inclusion will actually result in an inclusion.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
HashLoc | “(file):(line):(col)” | SourceLocation | The location of the ‘#’ that starts the inclusion directive.
IncludeTok | (token) | const Token | The token that indicates the kind of inclusion directive, e.g., ‘include’ or ‘import’.
FileName | “(file)” | StringRef | The name of the file being included, as written in the source code.
IsAngled | (true|false) | bool | Whether the file name was enclosed in angle brackets; otherwise, it was enclosed in quotes.
FilenameRange | “(file)” | CharSourceRange | The character range of the quotes or angle brackets for the written file name.
File | “(file)” | const FileEntry | The actual file that may be included by this inclusion directive.
SearchPath | “(path)” | StringRef | Contains the search path which was used to find the file in the file system.
RelativePath | “(path)” | StringRef | The path relative to SearchPath, at which the include file was found.
Imported | ((module name)|(null)) | const Module | The module, whenever an inclusion directive was automatically turned into a module import or null otherwise.

Example::

    - Callback: InclusionDirective
      HashLoc: "D:/Clang/llvmnewmod/clang-tools-extra/test/pp-trace/pp-trace-include.cpp:4:1"
      IncludeTok: include
      FileName: "Input/Level1B.h"
      IsAngled: false
      FilenameRange: "Input/Level1B.h"
      File: "D:/Clang/llvmnewmod/clang-tools-extra/test/pp-trace/Input/Level1B.h"
      SearchPath: "D:/Clang/llvmnewmod/clang-tools-extra/test/pp-trace"
      RelativePath: "Input/Level1B.h"
      Imported: (null)

#### moduleImport Callback

moduleImport is called when there was an explicit module-import syntax.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
ImportLoc | “(file):(line):(col)” | SourceLocation | The location of import directive token.
Path | “(path)” | ModuleIdPath | The identifiers (and their locations) of the module “path”.
Imported | ((module name)|(null)) | const Module | The imported module; can be null if importing failed.

Example::

    - Callback: moduleImport
      ImportLoc: "d:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-modules.cpp:4:2"
      Path: [{Name: Level1B, Loc: "d:/Clang/llvmnewmod/clang-tools-extra/test/pp-trace/pp-trace-modules.cpp:4:9"}, {Name: Level2B, Loc: "d:/Clang/llvmnewmod/clang-tools-extra/test/pp-trace/pp-trace-modules.cpp:4:17"}]
      Imported: Level2B

#### EndOfMainFile Callback

EndOfMainFile is called when the end of the main file is reached.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
(no arguments) |  |  |

Example::

    - Callback: EndOfMainFile

#### Ident Callback

Ident is called when a #ident or #sccs directive is read.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
str | (name) | const std::string | The text of the directive.

Example::

    - Callback: Ident
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-ident.cpp:3:1"
      str: "$Id$"

#### PragmaDirective Callback

PragmaDirective is called when start reading any pragma directive.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Introducer | (PIK_HashPragma|PIK__Pragma|PIK___pragma) | PragmaIntroducerKind | The type of the pragma directive.

Example::

    - Callback: PragmaDirective
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
      Introducer: PIK_HashPragma

#### PragmaComment Callback

PragmaComment is called when a #pragma comment directive is read.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Kind | ((name)|(null)) | const IdentifierInfo | The comment kind symbol.
Str | (message directive) | const std::string | The comment message directive.

Example::

    - Callback: PragmaComment
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
      Kind: library
      Str: kernel32.lib

#### PragmaDetectMismatch Callback

PragmaDetectMismatch is called when a #pragma detect_mismatch directive is read.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Name | “(name)” | const std::string | The name.
Value | (string) | const std::string | The value.

Example::

    - Callback: PragmaDetectMismatch
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
      Name: name
      Value: value

#### PragmaDebug Callback

PragmaDebug is called when a #pragma clang __debug directive is read.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
DebugType | (string) | StringRef | Indicates type of debug message.

Example::

    - Callback: PragmaDebug
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
      DebugType: warning

#### PragmaMessage Callback

PragmaMessage is called when a #pragma message directive is read.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Namespace | (name) | StringRef | The namespace of the message directive.
Kind | (PMK_Message|PMK_Warning|PMK_Error) | PPCallbacks::PragmaMessageKind | The type of the message directive.
Str | (string) | StringRef | The text of the message directive.

Example::

    - Callback: PragmaMessage
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
      Namespace: "GCC"
      Kind: PMK_Message
      Str: The message text.

#### PragmaDiagnosticPush Callback

PragmaDiagnosticPush is called when a #pragma gcc diagnostic push directive is read.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Namespace | (name) | StringRef | Namespace name.

Example::

    - Callback: PragmaDiagnosticPush
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
      Namespace: "GCC"

#### PragmaDiagnosticPop Callback

PragmaDiagnosticPop is called when a #pragma gcc diagnostic pop directive is read.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Namespace | (name) | StringRef | Namespace name.

Example::

    - Callback: PragmaDiagnosticPop
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
      Namespace: "GCC"

#### PragmaDiagnostic Callback

PragmaDiagnostic is called when a #pragma gcc diagnostic directive is read.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Namespace | (name) | StringRef | Namespace name.
mapping | (0|MAP_IGNORE|MAP_WARNING|MAP_ERROR|MAP_FATAL) | diag::Severity | Mapping type.
Str | (string) | StringRef | Warning/error name.

Example::

    - Callback: PragmaDiagnostic
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
      Namespace: "GCC"
      mapping: MAP_WARNING
      Str: WarningName

#### PragmaOpenCLExtension Callback

PragmaOpenCLExtension is called when OpenCL extension is either disabled or enabled with a pragma.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
NameLoc | “(file):(line):(col)” | SourceLocation | The location of the name.
Name | (name) | const IdentifierInfo | Name symbol.
StateLoc | “(file):(line):(col)” | SourceLocation | The location of the state.
State | (1|0) | unsigned | Enabled/disabled state.

Example::

    - Callback: PragmaOpenCLExtension
      NameLoc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-pragma.cpp:3:10"
      Name: Name
      StateLoc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-pragma.cpp:3:18"
      State: 1

#### PragmaWarning Callback

PragmaWarning is called when a #pragma warning directive is read.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
WarningSpec | (string) | StringRef | The warning specifier.
Ids | [(number)[, …]] | ArrayRef<int> | The warning numbers.

Example::

    - Callback: PragmaWarning
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
      WarningSpec: disable
      Ids: 1,2,3

#### PragmaWarningPush Callback

PragmaWarningPush is called when a #pragma warning(push) directive is read.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
Level | (number) | int | Warning level.

Example::

    - Callback: PragmaWarningPush
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-pragma.cpp:3:1"
      Level: 1

#### PragmaWarningPop Callback

PragmaWarningPop is called when a #pragma warning(pop) directive is read.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.

Example::

    - Callback: PragmaWarningPop
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-pragma.cpp:3:1"

#### MacroExpands Callback

MacroExpands is called when ::HandleMacroExpandedIdentifier when a macro invocation is found.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
MacroNameTok | (token) | const Token | The macro name token.
MacroDirective | (MD_Define|MD_Undefine|MD_Visibility) | const MacroDirective | The kind of macro directive from the MacroDirective structure.
Range | [“(file):(line):(col)”, “(file):(line):(col)”] | SourceRange | The source range for the expansion.
Args | [(name)|(number)|<(token name)>[, …]] | const MacroArgs | The argument tokens. Names and numbers are literal, everything else is of the form ‘<’ tokenName ‘>’.

Example::

    - Callback: MacroExpands
      MacroNameTok: X_IMPL
      MacroDirective: MD_Define
      Range: [(nonfile), (nonfile)]
      Args: [a <plus> y, b]

#### MacroDefined Callback

MacroDefined is called when a macro definition is seen.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
MacroNameTok | (token) | const Token | The macro name token.
MacroDirective | (MD_Define|MD_Undefine|MD_Visibility) | const MacroDirective | The kind of macro directive from the MacroDirective structure.

Example::

    - Callback: MacroDefined
      MacroNameTok: X_IMPL
      MacroDirective: MD_Define

#### MacroUndefined Callback

MacroUndefined is called when a macro #undef is seen.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
MacroNameTok | (token) | const Token | The macro name token.
MacroDirective | (MD_Define|MD_Undefine|MD_Visibility) | const MacroDirective | The kind of macro directive from the MacroDirective structure.

Example::

    - Callback: MacroUndefined
      MacroNameTok: X_IMPL
      MacroDirective: MD_Define

#### Defined Callback

Defined is called when the ‘defined’ operator is seen.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
MacroNameTok | (token) | const Token | The macro name token.
MacroDirective | (MD_Define|MD_Undefine|MD_Visibility) | const MacroDirective | The kind of macro directive from the MacroDirective structure.
Range | [“(file):(line):(col)”, “(file):(line):(col)”] | SourceRange | The source range for the directive.

Example::

    - Callback: Defined
      MacroNameTok: MACRO
      MacroDirective: (null)
      Range: ["D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-macro.cpp:8:5", "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-macro.cpp:8:19"]

#### SourceRangeSkipped Callback

SourceRangeSkipped is called when a source range is skipped.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Range | [“(file):(line):(col)”, “(file):(line):(col)”] | SourceRange | The source range skipped.

Example::

    - Callback: SourceRangeSkipped
      Range: [":/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-macro.cpp:8:2", ":/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-macro.cpp:9:2"]

#### If Callback

If is called when an #if is seen.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
ConditionRange | [“(file):(line):(col)”, “(file):(line):(col)”] | SourceRange | The source range for the condition.
ConditionValue | (true|false) | bool | The condition value.

Example::

    - Callback: If
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-macro.cpp:8:2"
      ConditionRange: ["D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-macro.cpp:8:4", "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-macro.cpp:9:1"]
      ConditionValue: false

#### Elif Callback

Elif is called when an #elif is seen.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
ConditionRange | [“(file):(line):(col)”, “(file):(line):(col)”] | SourceRange | The source range for the condition.
ConditionValue | (true|false) | bool | The condition value.
IfLoc | “(file):(line):(col)” | SourceLocation | The location of the directive.

Example::

    - Callback: Elif
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-macro.cpp:10:2"
      ConditionRange: ["D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-macro.cpp:10:4", "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-macro.cpp:11:1"]
      ConditionValue: false
      IfLoc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-macro.cpp:8:2"

#### Ifdef Callback

Ifdef is called when an #ifdef is seen.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
MacroNameTok | (token) | const Token | The macro name token.
MacroDirective | (MD_Define|MD_Undefine|MD_Visibility) | const MacroDirective | The kind of macro directive from the MacroDirective structure.

Example::

    - Callback: Ifdef
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-conditional.cpp:3:1"
      MacroNameTok: MACRO
      MacroDirective: MD_Define

#### Ifndef Callback

Ifndef is called when an #ifndef is seen.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the directive.
MacroNameTok | (token) | const Token | The macro name token.
MacroDirective | (MD_Define|MD_Undefine|MD_Visibility) | const MacroDirective | The kind of macro directive from the MacroDirective structure.

Example::

    - Callback: Ifndef
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-conditional.cpp:3:1"
      MacroNameTok: MACRO
      MacroDirective: MD_Define

#### Else Callback

Else is called when an #else is seen.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the else directive.
IfLoc | “(file):(line):(col)” | SourceLocation | The location of the if directive.

Example::

    - Callback: Else
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-macro.cpp:10:2"
      IfLoc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-macro.cpp:8:2"

#### Endif Callback

Endif is called when an #endif is seen.

Argument descriptions:

Argument Name | Argument Value Syntax | Clang C++ Type | Description
--- | --- | --- | ---
Loc | “(file):(line):(col)” | SourceLocation | The location of the endif directive.
IfLoc | “(file):(line):(col)” | SourceLocation | The location of the if directive.

Example::

    - Callback: Endif
      Loc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-macro.cpp:10:2"
      IfLoc: "D:/Clang/llvm/clang-tools-extra/test/pp-trace/pp-trace-macro.cpp:8:2"

## Building pp-trace

To build from source:

1. Read Getting Started with the LLVM System and Clang Tools Documentation for information on getting sources for LLVM, Clang, and Clang Extra Tools.

2. Getting Started with the LLVM System and Building LLVM with CMake give directions for how to build. With sources all checked out into the right place the LLVM build will build Clang Extra Tools and their dependencies automatically.

   - If using CMake, you can also use the `pp-trace` target to build just the pp-trace tool and its dependencies.