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Android/android-ndk-r27d/simpleperf/doc/jit_symbols.md

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+# JIT symbols
+
+[TOC]
+
+## Java JIT symbols
+
+On Android >= P, simpleperf supports profiling Java code, no matter whether it is executed by
+the interpreter, or JITed, or compiled into native instructions. So you don't need to do anything.
+
+For details on Android O and N, see
+[android_application_profiling.md](./android_application_profiling.md#prepare-an-android-application).
+
+## Generic JIT symbols
+
+Simpleperf supports picking up symbols from per-pid symbol map files, somewhat similar to what
+Linux kernel perftool does. Application should create those files at specific locations.
+
+### Symbol map file location for application
+
+Application should create symbol map files in its data directory.
+
+For example, process `123` of application `foo.bar.baz` should create
+`/data/data/foo.bar.baz/perf-123.map`.
+
+### Symbol map file location for standalone program
+
+Standalone programs should create symbol map files in `/data/local/tmp`.
+
+For example, standalone program process `123` should create `/data/local/tmp/perf-123.map`.
+
+### Symbol map file format
+
+Symbol map file is a text file.
+
+Every line describes a new symbol. Line format is:
+```
+<symbol-absolute-address> <symbol-size> <symbol-name>
+```
+
+For example:
+```
+0x10000000 0x16 jit_symbol_one
+0x20000000 0x332 jit_symbol_two
+0x20002004 0x8 jit_symbol_three
+```
+
+All characters after the symbol size and until the end of the line are parsed as the symbol name,
+with leading and trailing spaces removed. This means spaces are allowed in symbol names themselves.
+
+### Known issues
+
+Current implementation gets confused if memory pages where JIT symbols reside are reused by mapping
+a file either before or after.
+
+For example, if memory pages were first used by `dlopen("libfoo.so")`, then freed by `dlclose`,
+then allocated for JIT symbols - simpleperf will report symbols from `libfoo.so` instead.