a11e698749
The art apex already has access to bpf_headers which includes bpf_syscall_wrappers, but this extra line is needed to switch it away from needlessly linking libbpf_android. Since these are header files only, this annotation is kind of pointless, but it does turn out to be needed... Test: TreeHugger Signed-off-by: Maciej Żenczykowski <maze@google.com> Change-Id: I9e4d3373cea488080304e31ed7c8708aec988933
JNI
As a general rule, jarjar every static library dependency used in a mainline module into the modules's namespace (especially if it is also used by other modules)
Fully-qualified name of java class needs to be hard-coded into the JNI .so, because JNI_OnLoad does not take any parameters. This means that there needs to be a different .so target for each post-jarjared package, so for each module.
This is the guideline to provide JNI library shared with modules:
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provide a common java library in frameworks/libs/net with the Java class (e.g. BpfMap.java).
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provide a common native library in frameworks/libs/net with the JNI and provide the native register function with class_name parameter. See register_com_android_net_module_util_BpfMap function in frameworks/libs/net/common/native/bpfmapjni/com_android_net_module_util_BpfMap.cpp as an example.
When you want to use JNI library from frameworks/lib/net:
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Each module includes the java library (e.g. net-utils-device-common-bpf) and applies its jarjar rules after build.
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Each module creates a native library in their directory, which statically links against the common native library (e.g. libnet_utils_device_common_bpf), and calls the native registered function by hardcoding the post-jarjar class_name. Linkage MUST be static because common functions in the file (e.g.,
register_com_android_net_module_util_BpfMap) will appear in the library (.so) file, and different versions of the library loaded in the same process by different modules will in general have different versions. It's important that each of these libraries loads the common function from its own library. Static linkage should guarantee this because static linkage resolves symbols at build time, not runtime.