Fix llvm error: variable 'default_iv_length' and other may be used uninitialized

[sergio-nsk]

Description

mbedtls/library/psa_crypto.c:3428:30: error: variable 'default_iv_length' may be uninitialized when used here [-Werror,-Wconditional-uninitialized]
        memcpy(iv, local_iv, default_iv_length);
                             ^~~~~~~~~~~~~~~~~
mbedtls/library/psa_crypto.c:4646:36: error: variable 'required_nonce_size' may be uninitialized when used here [-Werror,-Wconditional-uninitialized]
        memcpy(nonce, local_nonce, required_nonce_size);
                                   ^~~~~~~~~~~~~~~~~~~
mbedtls/library/ssl_cache.c:309:54: error: variable 'session_serialized_len' may be uninitialized when used here [-Werror,-Wconditional-uninitialized]
        mbedtls_platform_zeroize(session_serialized, session_serialized_len);
                                                     ^~~~~~~~~~~~~~~~~~~~~~

The warnings are false positive, but treated as errors and prevent compiling on Windows with LLVM Clang.

Gatekeeper checklist

• changelog not required
• backport done mbedtls-2.28: Fix llvm error: variable 'default_iv_length' may be used uninitialized #7211
• tests not required

[tom-cosgrove-arm]

This doesn't give a fully clean build with -Wconditional-uninitialized - I haven't checked the backport

suites/test_suite_psa_crypto.function:9776:38: error: variable 'first_exported_length' may be uninitialized when used here
      [-Werror,-Wconditional-uninitialized]
        ASSERT_COMPARE(first_export, first_exported_length,
                                     ^~~~~~~~~~~~~~~~~~~~~
./include/test/macros.h:172:14: note: expanded from macro 'ASSERT_COMPARE'
        if ((size1) != 0)                                            \
             ^~~~~
suites/test_suite_psa_crypto.function:9676:33: note: initialize the variable 'first_exported_length' to silence this warning
    size_t first_exported_length;
                                ^
                                 = 0

[sergio-nsk]

I tried only UWP builds with LLVM clang and w/o test builds.

[tom-cosgrove-arm]

Could you share how you build for UWP?

[sergio-nsk]

With cmake using a toolchain file, that tunes cmake variables for using LLVM clang compiler (version 15.0.7).

cmake -S . -B out -G Ninja -DCMAKE_BUILD_TYPE=Debug CMAKE_SYSTEM_NAME=WindowsStore -DCMAKE_SYSTEM_VERSION=10.0 -DCMAKE_TOOLCHAIN_FILE=cmake/toolchain-clang.cmake

I suppose the toolchain file is not interesting. The compiler flags used are more interesting, they are set to CMAKE_C_FLAGS and CMAKE_CXX_FLAGS in CMakeLists.txt:

-Wall
-Wextra
-Wuninitialized
-Wsometimes-uninitialized
-Wconditional-uninitialized
-Wno-unused-function
-Wno-error=missing-braces
-Wno-deprecated
-Wno-unused-parameter
-Wno-missing-field-initializers
-Wstrict-prototypes
-Wimplicit-fallthrough
-Wwrite-strings
-Werror

[tom-cosgrove-arm]

LGTM

[davidhorstmann-arm]

LGTM