docs/TESTING_WITH_SANITIZERS.md

   1 ---
   2 title: Testing systemd using sanitizers
   3 ---
   4
   5 # Testing systemd using sanitizers
   6
   7 To catch the *nastier* kind of bugs, you can run your code with [Address Sanitizer](https://clang.llvm.org/docs/AddressSanitizer.html)
   8 and [Undefined Behavior Sanitizer](https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html).
   9 This is mostly done automagically by various CI systems for each PR, but you may
  10 want to do it locally as well. The process slightly varies depending on the
  11 compiler you want to use and which part of the test suite you want to run.
  12
  13 ## gcc
  14 gcc compiles in sanitizer libraries dynamically by default, so you need to get
  15 the shared libraries first - on Fedora these are shipped as a separate packages
  16 (`libasan` for Address Sanitizer and `libubsan` for Undefined Behavior Sanitizer).
  17
  18 The compilation itself is then a matter of simply adding `-Db_sanitize=address,undefined`
  19 to `meson`. That's it - following executions of `meson test` and integrations tests
  20 under `test/` subdirectory will run with sanitizers enabled. However, to get
  21 truly useful results, you should tweak the runtime configuration of respective
  22 sanitizers; e.g. in systemd we set the following environment variables:
  23
  24 ```bash
  25 ASAN_OPTIONS=strict_string_checks=1:detect_stack_use_after_return=1:check_initialization_order=1:strict_init_order=1
  26 UBSAN_OPTIONS=print_stacktrace=1:print_summary=1:halt_on_error=1
  27 ```
  28 ## clang
  29 In case of clang things are somewhat different - the sanitizer libraries are
  30 compiled in statically by default. This is not an issue if you plan to run
  31 only the unit tests, but for integration tests you'll need to convince clang
  32 to use the dynamic versions of sanitizer libraries.
  33
  34 First of all, pass `-shared-libsan` to both `clang` and `clang++`:
  35
  36 ```bash
  37 CFLAGS=-shared-libasan
  38 CXXFLAGS=-shared-libasan
  39 ```
  40
  41 The `CXXFLAGS` are necessary for `src/libsystemd/sd-bus/test-bus-vtable-cc.c`. Compilation
  42 is then the same as in case of gcc, simply add `-Db_sanitize=address,undefined`
  43 to the `meson` call and use the same environment variables for runtime configuration.
  44
  45 ```bash
  46 ASAN_OPTIONS=strict_string_checks=1:detect_stack_use_after_return=1:check_initialization_order=1:strict_init_order=1
  47 UBSAN_OPTIONS=print_stacktrace=1:print_summary=1:halt_on_error=1
  48 ```
  49
  50 After this, you'll probably notice that all compiled binaries complain about
  51 missing `libclang_rt.asan*` library. To fix this, you have to install clang's
  52 runtime libraries, usually shipped in the `compiler-rt` package. As these libraries
  53 are installed in a non-standard location (non-standard for `ldconfig`), you'll
  54 need to manually direct binaries to the respective runtime libraries.
  55
  56 ```
  57 # Optionally locate the respective runtime DSO
  58 $ ldd build/systemd | grep libclang_rt.asan
  59         libclang_rt.asan-x86_64.so => not found
  60         libclang_rt.asan-x86_64.so => not found
  61 $ find /usr/lib* /usr/local/lib* -type f -name libclang_rt.asan-x86_64.so 2>/dev/null
  62 /usr/lib64/clang/7.0.1/lib/libclang_rt.asan-x86_64.so
  63
  64 # Set the LD_LIBRARY_PATH accordingly
  65 export LD_LIBRARY_PATH=/usr/lib64/clang/7.0.1/lib/
  66
  67 # If the path is correct, the "not found" message should change to an actual path
  68 $ ldd build/systemd | grep libclang_rt.asan
  69         libclang_rt.asan-x86_64.so => /usr/lib64/clang/7.0.1/lib/libclang_rt.asan-x86_64.so (0x00007fa9752fc000)
  70 ```
  71
  72 This should help binaries to correctly find necessary sanitizer DSOs.
  73
  74 Also, to make the reports useful, `llvm-symbolizer` tool is required (usually
  75 part of the `llvm` package).
  76
  77 ## Background notes
  78 The reason why you need to force dynamic linking in case of `clang` is that some
  79 applications make use of `libsystemd`, which is compiled with sanitizers as well.
  80 However, if a *standard* (uninstrumented) application loads an instrumented library,
  81 it will immediately fail due to unresolved symbols. To fix/workaround this, you
  82 need to pre-load the ASan DSO using `LD_PRELOAD=/path/to/asan/dso`, which will
  83 make things work as expected in most cases. This will, obviously, not work with
  84 statically linked sanitizer libraries.
  85
  86 These shenanigans are performed automatically when running the integration test
  87 suite (i.e. `test/TEST-??-*`) and are located in `test/test-functions` (mainly,
  88 but not only, in the `create_asan_wrapper` function).