CMAKE-INSTRUMENTATION(7)

NAME
cmake-instrumentation - CMake Instrumentation

Added in version 4.0.

INTRODUCTION

Note:
        This feature is only available when experimental support for instrumentation has been enabled by the CMAKE_EXPERIMENTAL_INSTRUMENTATION gate.

The CMake Instrumentation API allows for the collection of timing data, target information and system diagnostic information during the configure, generate, build, test and install steps for a CMake project.

This feature is only available for projects using the Makefile Generators <#makefile-generators>, Ninja Generators <#ninja-generators> or FASTBuild <#generator:FASTBuild>.

All interactions with the CMake instrumentation API must specify both an API version and a Data version. At this time, there is only one version for each of these: the API v1 and Data v1.

  Data Collection

Whenever a command is executed with instrumentation enabled, a v1 Snippet File is created in the project build tree with data specific to that command. These files remain until after Indexing occurs.

CMake sets the RULE_LAUNCH_COMPILE <#prop_gbl:RULE_LAUNCH_COMPILE>, RULE_LAUNCH_LINK <#prop_gbl:RULE_LAUNCH_LINK> and RULE_LAUNCH_CUSTOM <#prop_gbl:RULE_LAUNCH_CUSTOM> global properties to use the ctest --instrument launcher in order to capture details of each compile, link, and custom command respectively. If the project has been configured with CTestUseLaunchers <#module:CTestUseLaunchers>, ctest --instrument will also include the behavior usually performed by ctest --launch.

  Indexing

Indexing is the process of collating generated instrumentation data. Indexing occurs at specific intervals called hooks, such as after every build. These hooks are configured as part of the v1 Query Files. Whenever a hook is triggered, an index file is generated containing a list of snippet files newer than the previous indexing.

Indexing and can also be performed by manually invoking ctest --collect-instrumentation <build>.

  Callbacks

As part of the v1 Query Files, users can provide a list of callbacks intended to handle data collected by this feature.

Whenever Indexing occurs, each provided callback is executed, passing the path to the generated index file as an argument.

These callbacks, defined either at the user-level or project-level should read the instrumentation data and perform any desired handling of it. The index file and its listed snippets are automatically deleted by CMake once all callbacks have completed. Note that a callback should never move or delete these data files manually as they may be needed by other callbacks.

ENABLING INSTRUMENTATION

Instrumentation can be enabled either for an individual CMake project, or for all CMake projects configured and built by a user. For both cases, see the v1 Query Files for details on configuring this feature.

  Enabling Instrumentation at the Project-Level

Project code can contain instrumentation queries with the cmake_instrumentation() <#command:cmake_instrumentation> command.

In addition, query files can be placed manually under <build>/.cmake/instrumentation/<version>/query/ at the top of a build tree. This version of CMake supports only one version schema, API v1.

  Enabling Instrumentation at the User-Level

Instrumentation can be configured at the user-level by placing query files in the CMAKE_CONFIG_DIR <#envvar:CMAKE_CONFIG_DIR> under <config_dir>/instrumentation/<version>/query/.

  Enabling Instrumentation for CDash Submissions

You can enable instrumentation when using CTest in Dashboard Client <#dashboard-client> mode by setting the CTEST_USE_INSTRUMENTATION <#envvar:CTEST_USE_INSTRUMENTATION> environment variable. Doing so automatically enables the dynamicSystemInformation option.

The following table shows how each type of instrumented command gets mapped to a corresponding type of CTest XML file.
Snippet Role | CTest XML File
configure | Configure.xml
generate | Configure.xml
compile | Build.xml
link | Build.xml
custom | Build.xml
build | unused!
cmakeBuild | Build.xml
cmakeInstall | Build.xml
install | Build.xml
ctest | Build.xml
test | Test.xml

By default the command line reported to CDash is truncated at the first space. You can instead choose to report the full command line (including arguments) by setting CTEST_USE_VERBOSE_INSTRUMENTATION <#envvar:CTEST_USE_VERBOSE_INSTRUMENTATION> to 1.

Alternatively, you can use the v1 Query Files to enable instrumentation for CDash using the cdashSubmit and cdashVerbose options.

In order for the submitted Build.xml file to group the snippet files correctly, all configure and build commands should be executed with CTest in Dashboard Client mode.

API V1

The API version specifies the layout of the instrumentation directory, as well as the general format of the query files and cmake_instrumentation() <#command:cmake_instrumentation> command arguments.

The Instrumentation API v1 is housed in the instrumentation/v1/ directory under either <build>/.cmake/ for output data and project-level queries, or <config_dir>/ for user-level queries. The v1 component of this directory is what signifies the API version. It has the following subdirectories:

    query/
        Holds query files written by users or clients. Any file with the .json file extension will be recognized as a query file. These files are owned by whichever client or user creates them.

    query/generated/
        Holds query files generated by a CMake project with the cmake_instrumentation() <#command:cmake_instrumentation> command or the CTEST_USE_INSTRUMENTATION <#envvar:CTEST_USE_INSTRUMENTATION> variable. These files are owned by CMake and are deleted and regenerated automatically during the CMake configure step.

    data/
        Holds instrumentation data collected on the project. CMake owns all data files, they should never be removed by other processes. Data collected here remains until after Indexing occurs and all Callbacks are executed.

    data/index/
        A subset of the collected data, containing any v1 Index Files.

    data/content/
        A subset of the collected data, containing any v1 CMake Content Files.

    data/trace/
        A subset of the collected data, containing the Google Trace File created from the most recent Indexing. Unlike other data files, the most recent trace file remains even after Indexing occurs and all Callbacks are executed, until the next time Indexing occurs.

    cdash/
        Holds temporary files used internally to generate XML content to be submitted to CDash.

  v1 Query Files

Any file with the .json extension under the instrumentation/v1/query/ directory is recognized as a query for instrumentation data.

These files must contain a JSON object with the following keys. The version key is required, but all other fields are optional.

    version
        The Data version of snippet file to generate, an integer. Currently the only supported version is 1.

    callbacks
        A list of command-line strings for Callbacks to handle collected instrumentation data. Whenever these callbacks are executed, the full path to a v1 Index File is appended to the arguments included in the string.

    hooks
        A list of strings specifying when Indexing should occur automatically. These are the intervals when instrumentation data should be collated and user Callbacks should be invoked to handle the data. Elements in this list should be one of the following:

        •   postGenerate

        •   preBuild (called when ninja or make is invoked)

        •   postBuild (called when ninja or make completes)

        •   preCMakeBuild (called when cmake --build is invoked)

        •   postCMakeBuild (called when cmake --build completes)

        •   postCMakeInstall

        •   postCTest

    preBuild and postBuild are not supported when using the MSYS Makefiles <#generator:MSYS Makefiles> or FASTBuild <#generator:FASTBuild> generators. Additionally, they will not be triggered when the build tool is invoked by cmake --build.

    options
        A list of strings used to enable certain optional behavior, including the collection of certain additional data. Elements in this list should be one of the following:

                staticSystemInformation
                    Enables collection of the static information about the host machine CMake is being run from. This data is collected during Indexing and is included in the generated v1 Index File.

                dynamicSystemInformation
                    Enables collection of the dynamic information about the host machine CMake is being run from. Data is collected for every v1 Snippet File generated by CMake, and includes information from immediately before and after the command is executed.

                cdashSubmit
                    Enables including instrumentation data in CDash. This does not automatically enable dynamicSystemInformation, but is otherwise equivalent to having the CTEST_USE_INSTRUMENTATION <#envvar:CTEST_USE_INSTRUMENTATION> environment variable enabled.

                cdashVerbose
                    Enables including the full untruncated commands in data submitted to CDash. Equivalent to having the CTEST_USE_VERBOSE_INSTRUMENTATION <#envvar:CTEST_USE_VERBOSE_INSTRUMENTATION> environment variable enabled.

                trace
                    Enables generation of a Google Trace File during Indexing to visualize data from the v1 Snippet Files collected.

The callbacks listed will be invoked during the specified hooks at a minimum. When there are multiple query files, the callbacks, hooks and options between them will be merged. Therefore, if any query file includes any hooks, every callback across all query files will be executed at every hook across all query files. Additionally, if any query file requests optional data using the options field, any related data will be present in all snippet files. User written callbacks should be able to handle the presence of this optional data, since it may be requested by an unrelated query.

Example:

            {
              "version": 1,
              "callbacks": [
                "/usr/bin/python callback.py",
                "/usr/bin/cmake -P callback.cmake arg",
              ],
              "hooks": [
                "postCMakeBuild",
                "postCMakeInstall"
              ],
              "options": [
                "staticSystemInformation",
                "dynamicSystemInformation",
                "cdashSubmit",
                "trace"
              ]
            }

In this example, after every cmake --build or cmake --install invocation, an index file index-<timestamp>.json will be generated in <build>/.cmake/instrumentation/v1/data/index containing a list of data snippet files created since the previous indexing. The commands /usr/bin/python callback.py index-<timestamp>.json and /usr/bin/cmake -P callback.cmake arg index-<timestamp>.json will be executed in that order. The index file will contain the staticSystemInformation data and each snippet file listed in the index will contain the dynamicSystemInformation data. Additionally, the index file will contain the path to the generated Google Trace File. Once both callbacks have completed, the index file and data files listed by it (including snippet files, but not the trace file) will be deleted from the project build tree. The instrumentation data will be present in the XML files submitted to CDash, but with truncated command strings because cdashVerbose was not enabled.

DATA V1

Data version specifies the contents of the output files generated by the CMake instrumentation API as part of the Data Collection and Indexing. A new version number will be created whenever previously included data is removed or reformatted such that scripts written to parse this data may become incompatible with the new format. There are four types of data files generated: the v1 Snippet File, v1 Index File, v1 CMake Content File, and the Google Trace File. When using the API v1, these files live in <build>/.cmake/instrumentation/v1/data/ under the project build tree.

  v1 Snippet File

Snippet files are generated for every compile, link and custom command invoked as part of the CMake build or install step and contain instrumentation data about the command executed. Additionally, snippet files are created for the following:

    •   The CMake configure step

    •   The CMake generate step

    •   Entire build step (executed with cmake --build)

    •   Entire install step (executed with cmake --install)

    •   Each ctest invocation

    •   Each individual test executed by ctest.

These files remain in the build tree until after Indexing occurs and any user-specified Callbacks are executed.

Snippet files have a filename with the syntax <role>-<hash>-<timestamp>.json and contain the following data:

            version
                The Data version of the snippet file, an integer. Currently the version is always 1.

            command
                The full command executed. Excluded when role is build.

            workingDir
                The working directory in which the command was executed.

            result
                The exit code of the command, an integer. This will be null when role is build.

            role
                The type of command executed, which will be one of the following values:

                •   configure: the CMake configure step

                •   generate: the CMake generate step

                •   compile: an individual compile step invoked during the build

                •   link: an individual link step invoked during the build

                •   custom: an individual custom command invoked during the build

                •   build: a complete make or ninja invocation (not through cmake --build).

                •   cmakeBuild: a complete cmake --build invocation

                •   cmakeInstall: a complete cmake --install invocation

                •   install: an individual cmake -P cmake_install.cmake invocation

                •   ctest: a complete ctest invocation

                •   test: a single test executed by CTest

            target
                The CMake target associated with the command. Only included when role is compile or link. In conjunction with cmakeContent, this can be used to look up the target type and labels.

            timeStart
                Time at which the command started, expressed as the number of milliseconds since the system epoch.

            duration
                The duration that the command ran for, expressed in milliseconds.

            outputs
                The command's output file(s), an array. Only included when role is one of: compile, link, custom.

            outputSizes
                The size(s) in bytes of the outputs, an array. For files which do not exist, the size is 0. Included under the same conditions as the outputs field.

            source
                The source file being compiled. Only included when role is compile.

            language
                The language of the source file being compiled. Only included when role is compile or link.

            testName
                The name of the test being executed. Only included when role is test.

            config
                The type of build, such as Release or Debug. Only included when role is one of: compile, link, custom, install, test.

            dynamicSystemInformation
                Specifies the dynamic information collected about the host machine CMake is being run from. Data is collected for every snippet file generated by CMake, with data immediately before and after the command is executed. Only included when enabled by the v1 Query Files.

                beforeHostMemoryUsed
                    The Host Memory Used in KiB at timeStart.

                afterHostMemoryUsed
                    The Host Memory Used in KiB at timeStart + duration.

                beforeCPULoadAverage
                    The Average CPU Load at timeStart, or null if it cannot be determined.

                afterCPULoadAverage
                    The Average CPU Load at timeStart + duration, or null if it cannot be determined.

            cmakeContent
                The path to a v1 CMake Content File located under data, which contains information about the CMake configure and generate steps responsible for generating the command in this snippet.

            showOnly
                A boolean representing whether the --show-only option was passed to ctest. Only included when role is ctest.

Example:

            {
              "version": 1,
              "command" : "\"/usr/bin/c++\" \"-MD\" \"-MT\" \"CMakeFiles/main.dir/main.cxx.o\" \"-MF\" \"CMakeFiles/main.dir/main.cxx.o.d\" \"-o\" \"CMakeFiles/main.dir/main.cxx.o\" \"-c\" \"<src>/main.cxx\"",
              "role" : "compile",
              "return" : 1,
              "target": "main",
              "language" : "C++",
              "outputs" : [ "CMakeFiles/main.dir/main.cxx.o" ],
              "outputSizes" : [ 0 ],
              "source" : "<src>/main.cxx",
              "config" : "Debug",
              "dynamicSystemInformation" :
              {
                "afterCPULoadAverage" : 2.3500000000000001,
                "afterHostMemoryUsed" : 6635680.0
                "beforeCPULoadAverage" : 2.3500000000000001,
                "beforeHostMemoryUsed" : 6635832.0
              },
              "timeStart" : 1737053448177,
              "duration" : 31,
              "cmakeContent" : "content/cmake-2025-07-11T12-46-32-0572.json"
            }

  v1 Index File

Index files contain a list of v1 Snippet Files. It serves as an entry point for navigating the instrumentation data. They are generated whenever Indexing occurs and deleted after any user-specified Callbacks are executed.

    version
        The Data version of the index file, an integer. Currently the version is always 1.

    buildDir
        The build directory of the CMake project.

    dataDir
        The full path to the <build>/.cmake/instrumentation/v1/data/ directory.

    hook
        The name of the hook responsible for generating the index file. In addition to the hooks that can be specified by one of the v1 Query Files, this value may be set to manual if indexing is performed by invoking ctest --collect-instrumentation <build>.

    snippets
        Contains a list of v1 Snippet Files. This includes all snippet files generated since the previous index file was created. The file paths are relative to dataDir.

    trace:
        Contains the path to the Google Trace File. This includes data from all corresponding snippets in the index file. The file path is relative to dataDir. Only included when enabled by the v1 Query Files.

    staticSystemInformation
        Specifies the static information collected about the host machine CMake is being run from. Only included when enabled by the v1 Query Files.

        •   OSName

        •   OSPlatform

        •   OSRelease

        •   OSVersion

        •   familyId

        •   hostname

        •   is64Bits

        •   modelId

        •   numberOfLogicalCPU

        •   numberOfPhysicalCPU

        •   processorAPICID

        •   processorCacheSize

        •   processorClockFrequency

        •   processorName

        •   totalPhysicalMemory

        •   totalVirtualMemory

        •   vendorID

        •   vendorString

Example:

            {
              "version": 1,
              "hook": "manual",
              "buildDir": "<build>",
              "dataDir": "<build>/.cmake/instrumentation/v1/data",
              "snippets": [
                "configure-<hash>-<timestamp>.json",
                "generate-<hash>-<timestamp>.json",
                "compile-<hash>-<timestamp>.json",
                "compile-<hash>-<timestamp>.json",
                "link-<hash>-<timestamp>.json",
                "install-<hash>-<timestamp>.json",
                "ctest-<hash>-<timestamp>.json",
                "test-<hash>-<timestamp>.json",
                "test-<hash>-<timestamp>.json",
              ],
              "trace": "trace/trace-<timestamp>.json"
            }

  v1 CMake Content File

CMake content files contain information about the CMake configure and generate steps. Each v1 Snippet File provides the path to one of these files corresponding to the CMake invocation responsible for generating its command.

Each CMake content file contains the following:

            custom
                An object containing arbitrary JSON data specified by the user with the Custom CMake Content <#cmake-instrumentation-custom-content> functionality of the cmake_instrumentation() <#command:cmake_instrumentation> command.

            targets
                An object containing CMake targets, indexed by name, that have corresponding instrumentation data. Each target contains the following:

                type
                    The target type. One of EXECUTABLE, STATIC_LIBRARY, SHARED_LIBRARY or OBJECT_LIBRARY.

                labels
                    The LABELS <#prop_tgt:LABELS> property of the target.

  Google Trace File

Trace files follow the Google Trace Event Format <https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/preview>. They include data from all v1 Snippet Files listed in the current index file. These files remain in the build tree even after Indexing occurs and all Callbacks are executed, until the next time Indexing occurs.

Trace files are stored in the JSON Array Format, where each v1 Snippet File corresponds to a single trace event object. Each trace event contains the following data:

    name
        A descriptive name generated by CMake based on the given snippet data.

    cat The role from the v1 Snippet File.

    ph  Currently, always "X" to represent Complete Events.

    ts  The timeStart from the v1 Snippet File, converted from milliseconds to microseconds.

    dur The duration from the v1 Snippet File, converted from milliseconds to microseconds.

    pid Unused (always zero).

    tid An integer ranging from zero to the number of concurrent jobs with which the processes being indexed ran. This is a synthetic ID calculated by CMake based on the ts and dur of all snippet files being indexed in order to produce a more useful visualization of the process concurrency.

    args
        Contains all data from the v1 Snippet File corresponding to this trace event.

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