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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). |