1# Native API Map Files 2 3Native APIs such as those exposed by the NDK, LL-NDK, or APEX are described by 4map.txt files. These files are [linker version scripts] with comments that are 5semantically meaningful to [gen_stub_libs.py]. For an example of a map file, see 6[libc.map.txt]. 7 8[gen_stub_libs.py]: https://cs.android.com/android/platform/superproject/+/master:build/soong/cc/gen_stub_libs.py 9[libc.map.txt]: https://cs.android.com/android/platform/superproject/+/master:bionic/libc/libc.map.txt 10[linker version scripts]: https://www.gnu.org/software/gnulib/manual/html_node/LD-Version-Scripts.html 11 12## Basic format 13 14A linker version script defines at least one alphanumeric "version" definition, 15each of which contain a list of symbols. For example: 16 17```txt 18MY_API_R { # introduced=R 19 global: 20 api_foo; 21 api_bar; 22 local: 23 *; 24}; 25 26MY_API_S { # introduced=S 27 global: 28 api_baz; 29} MY_API_R; 30``` 31 32Comments on the same line as either a version definition or a symbol name have 33meaning. If you need to add any comments that should not be interpreted by the 34stub generator, keep them on their own line. For a list of supported comments, 35see the "Tags" section. 36 37Here, `api_foo` and `api_bar` are exposed in the generated stubs with the 38`MY_API_R` version and `api_baz` is exposed with the `MY_API_S` version. No 39other symbols are defined as public by this API. `MY_API_S` inherits all symbols 40defined by `MY_API_R`. 41 42When generating NDK API stubs from this version script, the stub library for R 43will define `api_foo` and `api_bar`. The stub library for S will define all 44three APIs. 45 46Note that, with few exceptions (see "Special version names" below), the name of 47the version has no inherent meaning. 48 49These map files can (and should) also be used as version scripts for building 50the implementation library rather than just defining the stub interface by using 51the `version_script` property of `cc_library`. This has the effect of limiting 52symbol visibility of the library to expose only the interface named by the map 53file. Without this, APIs that you have not explicitly exposed will still be 54available to users via `dlsym`. Note: All comments are ignored in this case. Any 55symbol named in any `global:` group will be visible in the implementation 56library. Annotations in comments only affect what is exposed by the stubs. 57 58## Special version names 59 60Version names that end with `_PRIVATE` or `_PLATFORM` will not be exposed in any 61stubs, but will be exposed in the implementation library. Using either of these 62naming schemes is equivalent to marking the version with the `platform-only` 63tag. See the docs for `platform-only` for more information. 64 65## Tags 66 67Comments on the same line as a version definition or a symbol name are 68interpreted by the stub generator. Multiple space-delimited tags may be used on 69the same line. The supported tags are: 70 71### apex 72 73Indicates that the version or symbol is to be exposed by an APEX rather than the 74NDK. For APIs exposed by the platform *for* APEX, use `systemapi`. 75 76May be used in combination with `llndk` if the symbol is exposed to both APEX 77and the LL-NDK. 78 79### future 80 81Indicates that the version or symbol is first introduced in the "future" API 82level. This is an arbitrarily high API level used to define APIs that have not 83yet been added to a specific release. 84 85Warning: APIs marked `future` will be usable in any module with `sdk: "current"` 86but **will not be included in the NDK**. `future` should generally not be used, 87but is useful when developing APIs for an unknown future release. 88 89### introduced 90 91Indicates the version in which an API was first introduced. For example, 92`introduced=21` specifies that the API was first added (or first made public) in 93API level 21. This tag can be applied to either a version definition or an 94individual symbol. If applied to a version, all symbols contained in the version 95will have the tag applied. An `introduced` tag on a symbol overrides the value 96set for the version, if both are defined. 97 98Note: The map file alone does not contain all the information needed to 99determine which API level an API was added in. The `first_version` property of 100`ndk_library` will dictate which API levels stubs are generated for. If the 101module sets `first_version: "21"`, no symbols were introduced before API 21. 102**Symbol names for which no other rule applies will implicitly be introduced in 103`first_version`.** 104 105Code names can (and typically should) be used when defining new APIs. This 106allows the actual number of the API level to remain vague during development of 107that release. For example, `introduced=S` can be used to define APIs added in S. 108Any code name known to the build system can be used. For a list of versions 109known to the build system, see `out/soong/api_levels.json` (if not present, run 110`m out/soong/api_levels.json` to generate it). 111 112Architecture-specific variants of this tag exist: 113 114* `introduced-arm=VERSION` 115* `introduced-arm64=VERSION` 116* `introduced-x86=VERSION` 117* `introduced-x86_64=VERSION` 118 119The architecture-specific tag will take precedence over the architecture-generic 120tag when generating stubs for that architecture if both are present. If the 121symbol is defined with only architecture-specific tags, it will not be present 122for architectures that are not named. 123 124Note: The architecture-specific tags should, in general, not be used. These are 125primarily needed for APIs that were wrongly inconsistently exposed by libc/libm 126in old versions of Android before the stubs were well maintained. Think hard 127before using an architecture-specific tag for a new API. 128 129### llndk 130 131Indicates that the version or symbol is to be exposed in the LL-NDK stubs rather 132than the NDK. May be used in combination with `apex` if the symbol is exposed to 133both APEX and the LL-NDK. 134 135Historically this annotation was spelled `vndk`, but it has always meant LL-NDK. 136 137### platform-only 138 139Indicates that the version or symbol is public in the implementation library but 140should not be exposed in the stub library. Developers can still access them via 141`dlsym`, but they will not be exposed in the stubs so it should at least be 142clear to the developer that they are up to no good. 143 144The typical use for this tag is for exposing an API to the platform that is not 145for use by the NDK, LL-NDK, or APEX (similar to Java's `@SystemAPI`). It is 146preferable to keep such APIs in an entirely separate library to protect them 147from access via `dlsym`, but this is not always possible. 148 149### systemapi 150 151This is a synonym of the `apex` tag. It should be used to clarify that the API 152is an API exposed by the system for an APEX, whereas `apex` should be used for 153APIs exposed by an APEX to the platform or another APEX. 154 155### var 156 157Used to define a public global variable. By default all symbols are exposed as 158functions. In the uncommon situation of exposing a global variable, the `var` 159tag may be used. 160 161### versioned=VERSION 162 163Behaves similarly to `introduced` but defines the first version that the stub 164library should apply symbol versioning. For example: 165 166```txt 167R { # introduced=R 168 global: 169 foo; 170 bar; # versioned=S 171 local: 172 *; 173}; 174``` 175 176The stub library for R will contain symbols for both `foo` and `bar`, but only 177`foo` will include a versioned symbol `foo@R`. The stub library for S will 178contain both symbols, as well as the versioned symbols `foo@R` and `bar@R`. 179 180This tag is not commonly needed and is only used to hide symbol versioning 181mistakes that shipped as part of the platform. 182 183Note: Like `introduced`, the map file does not tell the whole story. The 184`ndk_library` Soong module may define a `unversioned_until` property that sets 185the default for the entire map file. 186 187### weak 188 189Indicates that the symbol should be [weak] in the stub library. 190 191[weak]: https://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/Function-Attributes.html 192