Signed-off-by: Yeqi Fu <fufuyqqq...@gmail.com> --- docs/native_calls.txt | 70 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 70 insertions(+) create mode 100644 docs/native_calls.txt
diff --git a/docs/native_calls.txt b/docs/native_calls.txt new file mode 100644 index 0000000000..8906566b13 --- /dev/null +++ b/docs/native_calls.txt @@ -0,0 +1,70 @@ +Native Library Calls Optimization for QEMU Linux-User +==================== + +Description +=========== +When running under the linux-user mode in QEMU, the entire program, +including all library calls, is translated. Many well-understood +library functions are usually optimized for the processor they run +on. For example, the semantics of memcpy are well-defined and +optimized. Instead of translating these library functions, we can +call their native versions, as the runtime of library functions +is generally biased towards a few core functions. Thus, only a +small subset of functions (such as mem* and str*) would need to +be hooked to be useful. + + +Implementation +============== +This feature introduces a set of specialized instructions for native +calls and provides helpers to translate these instructions to +corresponding native functions. A shared library is also implemented, +where native functions are rewritten as specialized instructions. +At runtime, user programs load the shared library, and specialized +instructions are executed when native functions are called. + +The specialized instructions are implemented using architecture- +specific macros. These macros utilize unused or invalid opcodes or +instruction fields to embed the necessary information for native +function calls. This approach ensures that the specialized +instructions do not conflict with existing instructions. + +For x86 and x86_64, the implementation uses an unused opcode. +For arm and aarch64, the HLT instruction is used, as it is invalid in +userspace and has 16 bits of spare immediate data. +For mips and mips64, the implementation takes advantage of unused +bytes in the syscall instruction. + +Supported Architectures +======================= +This feature is applicable to user programs with the following +architectures now: +- x86 +- x86_64 +- arm +- aarch64 +- mips +- mips64 + + +Usage +===== +1. Install Cross-Compilation Tools +Cross-compilation tools are required to build the shared libraries +that can hook the necessary library functions. For example, a viable +command on Ubuntu is: +``` +apt install libc6:i386 gcc-arm-linux-gnueabihf \ +gcc-aarch64-linux-gnu gcc-mips-linux-gnu gcc-mips64-linux-gnuabi64 +``` +2. Locate the Compiled libnative.so +After compilation, the libnative.so file can be found in the +`./build/common-user/native/<target>-linux-user` directory. + +3. Run the Program with the `--native-bypass` Option +To run your program with native library bypass, use the +`--native-bypass` option to import libnative.so: +``` +./build/qemu-<target> --native-bypass \ +./build/common-user/native/<target>-linux-user/libnative.so ./program +``` -- 2.34.1
