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91 lines
4.2 KiB
Markdown
91 lines
4.2 KiB
Markdown
---
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title: Testing systemd Using Sanitizers
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category: Contributing
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layout: default
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---
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# Testing systemd Using Sanitizers
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To catch the *nastier* kind of bugs, you can run your code with [Address Sanitizer](https://clang.llvm.org/docs/AddressSanitizer.html)
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and [Undefined Behavior Sanitizer](https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html).
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This is mostly done automagically by various CI systems for each PR, but you may
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want to do it locally as well. The process slightly varies depending on the
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compiler you want to use and which part of the test suite you want to run.
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## gcc
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gcc compiles in sanitizer libraries dynamically by default, so you need to get
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the shared libraries first - on Fedora these are shipped as a separate packages
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(`libasan` for Address Sanitizer and `libubsan` for Undefined Behavior Sanitizer).
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The compilation itself is then a matter of simply adding `-Db_sanitize=address,undefined`
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to `meson`. That's it - following executions of `meson test` and integrations tests
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under `test/` subdirectory will run with sanitizers enabled. However, to get
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truly useful results, you should tweak the runtime configuration of respective
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sanitizers; e.g. in systemd we set the following environment variables:
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```bash
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ASAN_OPTIONS=strict_string_checks=1:detect_stack_use_after_return=1:check_initialization_order=1:strict_init_order=1
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UBSAN_OPTIONS=print_stacktrace=1:print_summary=1:halt_on_error=1
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```
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## clang
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In case of clang things are somewhat different - the sanitizer libraries are
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compiled in statically by default. This is not an issue if you plan to run
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only the unit tests, but for integration tests you'll need to convince clang
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to use the dynamic versions of sanitizer libraries.
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First of all, pass `-shared-libsan` to both `clang` and `clang++`:
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```bash
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CFLAGS=-shared-libasan
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CXXFLAGS=-shared-libasan
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```
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The `CXXFLAGS` are necessary for `src/libsystemd/sd-bus/test-bus-vtable-cc.c`. Compilation
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is then the same as in case of gcc, simply add `-Db_sanitize=address,undefined`
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to the `meson` call and use the same environment variables for runtime configuration.
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```bash
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ASAN_OPTIONS=strict_string_checks=1:detect_stack_use_after_return=1:check_initialization_order=1:strict_init_order=1
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UBSAN_OPTIONS=print_stacktrace=1:print_summary=1:halt_on_error=1
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```
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After this, you'll probably notice that all compiled binaries complain about
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missing `libclang_rt.asan*` library. To fix this, you have to install clang's
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runtime libraries, usually shipped in the `compiler-rt` package. As these libraries
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are installed in a non-standard location (non-standard for `ldconfig`), you'll
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need to manually direct binaries to the respective runtime libraries.
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```
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# Optionally locate the respective runtime DSO
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$ ldd build/systemd | grep libclang_rt.asan
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libclang_rt.asan-x86_64.so => not found
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libclang_rt.asan-x86_64.so => not found
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$ find /usr/lib* /usr/local/lib* -type f -name libclang_rt.asan-x86_64.so 2>/dev/null
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/usr/lib64/clang/7.0.1/lib/libclang_rt.asan-x86_64.so
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# Set the LD_LIBRARY_PATH accordingly
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export LD_LIBRARY_PATH=/usr/lib64/clang/7.0.1/lib/
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# If the path is correct, the "not found" message should change to an actual path
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$ ldd build/systemd | grep libclang_rt.asan
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libclang_rt.asan-x86_64.so => /usr/lib64/clang/7.0.1/lib/libclang_rt.asan-x86_64.so (0x00007fa9752fc000)
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```
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This should help binaries to correctly find necessary sanitizer DSOs.
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Also, to make the reports useful, `llvm-symbolizer` tool is required (usually
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part of the `llvm` package).
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## Background notes
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The reason why you need to force dynamic linking in case of `clang` is that some
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applications make use of `libsystemd`, which is compiled with sanitizers as well.
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However, if a *standard* (uninstrumented) application loads an instrumented library,
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it will immediately fail due to unresolved symbols. To fix/workaround this, you
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need to pre-load the ASan DSO using `LD_PRELOAD=/path/to/asan/dso`, which will
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make things work as expected in most cases. This will, obviously, not work with
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statically linked sanitizer libraries.
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These shenanigans are performed automatically when running the integration test
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suite (i.e. `test/TEST-??-*`) and are located in `test/test-functions` (mainly,
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but not only, in the `create_asan_wrapper` function).
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