Uninitialised variable in ec_GFp_mont_batch_get_window

[giordano]

Problem:

When building v1.15.0 targeting 32-bit ARM architectures like armv6l or armv7l I get:

[00:20:47] In file included from /workspace/srcdir/aws-lc/crypto/fipsmodule/bcm.c:96:0:
[00:20:47] /workspace/srcdir/aws-lc/crypto/fipsmodule/ec/simple_mul.c: In function ‘ec_GFp_mont_batch_get_window’:
[00:20:47] /workspace/srcdir/aws-lc/crypto/fipsmodule/ec/felem.c:65:19: error: ‘neg_Y.words[0]’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
[00:20:47]      out->words[i] &= mask;
[00:20:47]                    ^~
[00:20:47] cc1: all warnings being treated as errors

Relevant details

AWS-LC commit: (aa90e50)

System information: for linux, below info can be collected by running uname -srvmp

• target CPU architecture: armv6l or armv7l
• CPU name: N/A
• OS: Linux

Build log:

[00:20:24]  ---> cmake -DCMAKE_INSTALL_PREFIX=${prefix} -DCMAKE_TOOLCHAIN_FILE=${CMAKE_TARGET_TOOLCHAIN} -DBUILD_TESTING=OFF -DCMAKE_BUILD_TYPE=Release -DDISABLE_GO=ON -DBUILD_SHARED_LIBS=OFF -GNinja ..
[00:20:24] -- The C compiler identification is GNU 7.1.0
[00:20:24] -- Detecting C compiler ABI info
[00:20:25] -- Detecting C compiler ABI info - done
[00:20:25] -- Check for working C compiler: /opt/bin/armv6l-linux-gnueabihf-libgfortran4-cxx11/arm-linux-gnueabihf-gcc - skipped
[00:20:25] -- Detecting C compile features
[00:20:25] -- Detecting C compile features - done
[00:20:25] -- The CXX compiler identification is GNU 7.1.0
[00:20:25] -- Detecting CXX compiler ABI info
[00:20:25] -- Detecting CXX compiler ABI info - done
[00:20:25] -- Check for working CXX compiler: /opt/bin/armv6l-linux-gnueabihf-libgfortran4-cxx11/arm-linux-gnueabihf-g++ - skipped
[00:20:25] -- Detecting CXX compile features
[00:20:25] -- Detecting CXX compile features - done
[00:20:25] -- Found Perl: /usr/bin/perl (found version "5.34.0")
[00:20:25] -- Go not found. Disabling some code generation and using pre-generated code in generated-src/
[00:20:25] -- Run check_run file_to_test 'memcmp_invalid_stripped_check.c', flag_to_set 'MEMCMP_INVALID_STRIPPED', and compile_flags '-O3 -DNDEBUG'.
[00:20:25] -- stdalign_check.c probe is positive, enabling AWS_LC_STDALIGN_AVAILABLE
[00:20:25] -- builtin_swap_check.c probe is positive, enabling AWS_LC_BUILTIN_SWAP_SUPPORTED
[00:20:25] -- The ASM compiler identification is GNU
[00:20:25] -- Found assembler: /opt/bin/armv6l-linux-gnueabihf-libgfortran4-cxx11/arm-linux-gnueabihf-gcc
[00:20:25] -- Looking for pthread.h
[00:20:25] -- Looking for pthread.h - found
[00:20:25] -- Performing Test CMAKE_HAVE_LIBC_PTHREAD
[00:20:25] -- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Failed
[00:20:25] -- Looking for pthread_create in pthreads
[00:20:25] -- Looking for pthread_create in pthreads - not found
[00:20:25] -- Looking for pthread_create in pthread
[00:20:26] -- Looking for pthread_create in pthread - found
[00:20:26] -- Found Threads: TRUE
[00:20:26] -- Configuring done
[00:20:26] -- Generating done
[00:20:26] -- Build files have been written to: /workspace/srcdir/aws-lc/build

Side note, it'd be very much appreciated if -Werror wasn't enforced, or at very least if it was possible to easily disable it without having to manually hack the CMake file.

[justsmth]

Thanks for reporting. I'll try to resolve the warning/error.

We'll also consider the possibility of removing the enforcement of -Werror. We want such strict enforcement for our own CI/testing, but it can be an obstacle for people building on compilers/platforms not fully covered by our CI.

[justsmth]

Hello -- I discussed with the team adding a build flag to allow compiler warnings to be ignored (i.e., allow warnings to NOT be errors). Our current consensus is that we prefer compiler warnings to always prevent our build from succeeding. Such warnings are important in helping us and our customers become aware of potential bugs and/or security concerns.

Please let us know any time you have a problem building AWS-LC. Thanks again for your report of this issue!