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Theory

Theroy

This page only introduce theroy of ULPatch, but not the implementation details.

All programs are single-threaded models, so you will not see synchronization locks in the code. Of course, we need to consider the multi-threaded situation of the target process.

ULPatch

Patch

The following figure shows the livepatch loading procedures.

ulpatch

The detailed steps are as follows:

  1. Compile source code into a relocatable ELF file, it's livepatch file;
  2. Load the relocatable ELF file into the target process address space;
  3. Relocate the symbols in the patch according to the target process address symbol table;
  4. Modify the patch function entry to jump to the patch function;

Unpatch

The following figure shows the uninstall procedures of the livepatch.

ulpatch::unpatch

The unpatch operation is the reverse operation of patch, but without the relocate process.

ULTask

It's an useful tool to modify target process, I call it Program Modifier. CONFIG_BUILD_ULTASK decides whether to compile ultask. Check manual ultask(8) to see more.

TODO

ULFtrace

Same as linux ftrace, need gcc -pg compile option. CONFIG_BUILD_ULFTRACE decides whether to compile ulftrace. Check manual ulftrace(8) to see more.

TODO