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Expand the rule for internal functions exposed for tests only

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Clarify that using a header in library/ rather than include/ for
internal functions is a rule, not just a possibility.

As suggested by Manuel, state a rule for functions that need to be
static for best optimization but that we want to unit-test.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2019-09-11 13:25:55 +02:00
parent 4b7279e5d9
commit fa51820e39
1 changed files with 4 additions and 2 deletions
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6
docs/architecture/testing/invasive-testing.md
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@ -24,7 +24,9 @@ Do not add test-specific interfaces if there's a practical way of doing it anoth
### Reliance on internal details
In unit tests and in test programs, it's ok to include header files from `library/`. In contrast, sample programs must not include header files from `library/`.
In unit tests and in test programs, it's ok to include header files from `library/`. Do not define non-public interfaces in public headers (`include/mbedtls` has `*_internal.h` headers for legacy reasons, but this approach is deprecated). In contrast, sample programs must not include header files from `library/`.
Sometimes it makes sense to have unit tests on functions that aren't part of the public API. Declare such functions in `library/*.h` and include the corresponding header in the test code. If the function should be `static` for optimization but can't be `static` for testing, declare it as `MBEDTLS_STATIC_TESTABLE`, and make the tests that use it depend on `MBEDTLS_TEST_HOOKS` (see [“rules for compile-time options”](#rules-for-compile-time-options)).
If test code or test data depends on internal details of the library and not just on its documented behavior, add a comment in the code that explains the dependency. For example:
@ -57,7 +59,7 @@ The code calls a function `mbedtls_foo()`. Usually this a macro defined to be a
Sometimes the substitutable function is a `static inline` function that does nothing (not a macro, to avoid accidentally skipping side effects in its parameters), to provide a hook for test code; such functions should have a name that starts with the prefix `mbedtls_test_hook_`. In such cases, the function should generally not modify its parameters, so any pointer argument should be const. The function should return void.
With `MBEDTLS_TEST_HOOKS` set, `mbedtls_foo` is a global variable of function pointer type. This global variable is initialized to the system function, or to a function that does nothing. The global variable is defined in a header in `library.h` such as `psa_crypto_invasive.h`.
With `MBEDTLS_TEST_HOOKS` set, `mbedtls_foo` is a global variable of function pointer type. This global variable is initialized to the system function, or to a function that does nothing. The global variable is defined in a header in the `library` directory such as `psa_crypto_invasive.h`.
In test code that needs to modify the internal behavior: