Why do I receive an array out of bounds error when building code generated with MATLAB Coder in R2024b?

I am using MATLAB Coder R2024b for ARM-cortex A using ARM GNU GCC v12.3 toolchain. When I attempt to build the generated code, I receive the following error message related to the file "coder_array.h":

In member function 'void coder::detail::data_ptr<T, SZ>::construct_last_n(T*, SZ) [with T = double; SZ = int]',
    inlined from 'void coder::detail::data_ptr<T, SZ>::reserve(SZ) [with T = double; SZ = int]' at path/to/coder_array.h:157:29,
    inlined from 'void coder::detail::data_ptr<T, SZ>::reserve(SZ) [with T = double; SZ = int]' at path/to/coder_array.h:154:10,
    inlined from 'void coder::detail::data_ptr<T, SZ>::resize(SZ) [with T = double; SZ = int]' at path/to/coder_array.h:172:20,
    inlined from 'void coder::array_base<T, SZ, N>::ensureCapacity(SZ) [with T = double; SZ = int; int N = 2]' at path/to/coder_array.h:783:21:
path/to/coder_array.h:196:17: error: array subscript 0 is outside array bounds of 'double [0]' [-Werror=array-bounds]
  196 |                 new (&_data[i]) T();
      |                 ^~~~~~~~~~~~~~~~~~~

Why is this error occurring?

Answer 1

[MathWorks Support Team]

This is a bug in GCC and a false error. This issue is only reproducible with the "-O3" or "-Warray-bounds" flags enabled. A fragment of the generated code from "coder_array.h" can be seen as:

for (i = size_ - _n; i < size_; i++) {
                new (&_data[i]) T();
}

This array allocates "_n" elements, but this allocation never occurs for 0 elements. GCC analyzer is conservatively analyzing the code. The analyzer of the compiler is not strong enough to understand that this 0 memory allocation can never occur.

In terms of a workaround, you can add the following to the beginning of the "reserve()" function in "coder_array.h":

if (_n <= 0)  {
    return;
}

An alternative workaround would be to change the compilation flags in your environment. If you remove the "-O3" or switch the "-Warray-bounds" flag to "–Wno-array-bounds" your code should compile successfully.