{"id":1804,"date":"2026-05-24T15:12:10","date_gmt":"2026-05-24T22:12:10","guid":{"rendered":"https:\/\/nanzhou.cc\/?p=1804"},"modified":"2026-05-24T15:12:10","modified_gmt":"2026-05-24T22:12:10","slug":"bazel-platforms","status":"publish","type":"post","link":"https:\/\/nanzhou.cc\/index.php\/2026\/05\/24\/bazel-platforms\/","title":{"rendered":"Bazel: platforms"},"content":{"rendered":"\n

Summary Table<\/h2>\n\n\n\n
Concept<\/strong><\/td>What it is<\/strong><\/td>Analogy<\/strong><\/td><\/tr><\/thead>
Constraint Setting<\/strong><\/td>A property category<\/td>“Vehicle Type”<\/td><\/tr>
Constraint Value<\/strong><\/td>A specific option<\/td>“Car”, “Truck”, “Motorcycle”<\/td><\/tr>
Platform<\/strong><\/td>A group of settings<\/td>“Vehicle configured for highway use” (Car + 4 Tires)<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

The Core Concepts<\/h3>\n\n\n\n

To understand how they relate, think of them in terms of a property-based system:<\/p>\n\n\n\n

    \n
  • constraint_setting<\/code><\/strong>: Defines a category<\/strong> or type of property that distinguishes machines (e.g., “CPU architecture”, “Operating System”).<\/li>\n\n\n\n
  • constraint_value<\/code><\/strong>: Defines a specific choice<\/strong> within a category (e.g., within the “CPU architecture” setting, choices could be “x86”, “ARM”, “RISC-V”).<\/li>\n\n\n\n
  • platform<\/code><\/strong>: A collection<\/strong> of constraint_values<\/code> that defines a complete environment (e.g., a “Linux-x86” platform is a collection of OS:Linux<\/code> and CPU:x86<\/code>).<\/li>\n<\/ul>\n\n\n\n

    Example: Defining Custom Constraints<\/h2>\n\n\n\n

    Suppose you are building an embedded system and you need to distinguish between different GPU types<\/strong> and glibc versions<\/strong>. You would define these in your own BUILD<\/code> file.<\/p>\n\n\n\n

    1. Define the “Categories” (Settings)<\/h4>\n\n\n\n

    Create a BUILD<\/code> file (e.g., \/\/tools\/platforms:BUILD<\/code>) to hold your custom logic.<\/p>\n\n\n\n

    # \/\/tools\/platforms\/BUILD\n\n# A new dimension for GPU hardware\nconstraint_setting(name = \"gpu_type\")\n\n# A new dimension for C library versions\nconstraint_setting(name = \"glibc_version\")\n<\/code><\/pre>\n\n\n\n
    2. Define the “Choices” (Values)<\/h4>\n\n\n\n
    Now, define the specific values that belong to those categories.<\/p>\n\n\n\n
    # \/\/tools\/platforms\/BUILD\n\n# Values for gpu_type\nconstraint_value(name = \"nvidia_rtx\", constraint_setting = \":gpu_type\")\nconstraint_value(name = \"amd_radeon\", constraint_setting = \":gpu_type\")\n\n# Values for glibc_version\nconstraint_value(name = \"glibc_2_25\", constraint_setting = \":glibc_version\")\nconstraint_value(name = \"glibc_2_28\", constraint_setting = \":glibc_version\")\n<\/code><\/pre>\n\n\n\n
    3. Bundle them into a Platform<\/h4>\n\n\n\n
    Now that you have defined these custom constraints, you can use them alongside standard ones to define your custom platform.<\/p>\n\n\n\n
    # \/\/tools\/platforms\/BUILD\n\nplatform(\n    name = \"custom_embedded_gpu_linux\",\n    constraint_values = [\n        \"@platforms\/\/os:linux\",          # Standard constraint\n        \"@platforms\/\/cpu:aarch64\",       # Standard constraint\n        \":nvidia_rtx\",                   # YOUR custom constraint\n        \":glibc_2_28\",                   # YOUR custom constraint\n    ],\n)\n<\/code><\/pre>\n\n\n\n
    How to use these in your build<\/h3>\n\n\n\n
    Once you’ve defined these, you can use select()<\/code> in your rules to change behavior based on these custom constraints.<\/p>\n\n\n\n
    # \/\/myapp\/BUILD\n\ncc_library(\n    name = \"gpu_driver\",\n    srcs = select({\n        \"\/\/tools\/platforms:nvidia_rtx\": [\"driver_nvidia.cc\"],\n        \"\/\/tools\/platforms:amd_radeon\": [\"driver_amd.cc\"],\n        \"\/\/conditions:default\": [\"driver_stub.cc\"],\n    }),\n)\n<\/code><\/pre>\n\n\n\n
    Why this approach is powerful:<\/h3>\n\n\n\n
      \n
    1. Strict Typing:<\/strong> Bazel ensures that nvidia_rtx<\/code> is only used for the gpu_type<\/code> setting. You can\u2019t accidentally assign it to an OS setting.<\/li>\n\n\n\n
    2. Organization:<\/strong> You keep your project-specific needs (like “is this a high-security build?”) inside your own repository, while using @platforms<\/code> for universal things like cpu<\/code> and os<\/code>.<\/li>\n\n\n\n
    3. Cross-Project Compatibility:<\/strong> If another team in your company wants to build for the same custom_embedded_gpu_linux<\/code> platform, they can import the label \/\/tools\/platforms:custom_embedded_gpu_linux<\/code> and get all the same settings.<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"
      Summary Table Concept What it is Analogy Constraint Setting A property category “Vehicle Type” Constraint Value A specific option “Car”, “Truck”, “Motorcycle” Platform A group of settings “Vehicle configured for highway use” (Car + 4 Tires) The Core Concepts To understand how they relate, think of them in terms of a property-based system: Example: Defining…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"0","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[77],"tags":[],"class_list":["post-1804","post","type-post","status-publish","format-standard","hentry","category-Toolchain"],"_links":{"self":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts\/1804","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/comments?post=1804"}],"version-history":[{"count":1,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts\/1804\/revisions"}],"predecessor-version":[{"id":1806,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts\/1804\/revisions\/1806"}],"wp:attachment":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/media?parent=1804"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/categories?post=1804"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/tags?post=1804"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}