Shader storage block name issue - c++

Question

Something weird is happening with my shader storage blocks.
I have 2 SSBs:
#version 450 core
out vec4 out_color;
layout (binding = 0, std430) buffer A_SSB
{
float a_data[];
};
layout (binding = 1, std430) buffer B_SSB
{
float b_data[];
};
void main()
{
a_data[0] = 0.0f;
a_data[1] = 1.0f;
a_data[2] = 2.0f;
a_data[3] = 3.0f;
b_data[0] = 90.0f;
b_data[1] = 81.0f;
b_data[2] = 72.0f;
b_data[3] = 63.0f;
out_color = vec4(0.0f, 0.8f, 1.0f, 1.0f);
}
This is working well, but if i swap the SSB names like that:
layout (binding = 0, std430) buffer B_SSB
{
float a_data[];
};
layout (binding = 1, std430) buffer A_SSB
{
float b_data[];
};
the SSB indexes are swapped although they are hardcoded and data which should be written to a_data is written to b_data and vice versa.
Both SSBs are 250MB large, the max size is more than 2GB. It seems that the indexes are allocated alphabetical but this shouldn't happen. I'm binding the buffers like that:
glCreateBuffers(1, &a_ssb);
glNamedBufferStorage(a_ssb, 7187400 * 9 * sizeof(float), nullptr, GL_MAP_READ_BIT);
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, a_ssb);
glShaderStorageBlockBinding(test_prog, 0, 0);
glCreateBuffers(1, &b_ssb);
glNamedBufferStorage(b_ssb, 7187400 * 9 * sizeof(float), nullptr, GL_MAP_READ_BIT);
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 1, b_ssb);
glShaderStorageBlockBinding(test_prog, 1, 1);
Is this a bug or my fault? Also i would like to ask why i'm getting the error "lvalue in array access too complex or possible array index out of bounds" if i'm assigning values in a for loop?
for(unsigned int i = 0; i < 4; ++i)
a_data[i] = float(i);

Answer 1

glShaderStorageBlockBinding(test_prog, 0, 0);
This is your problem.
You assigned the binding index in the shader. You do not need to assign it again.
Your problem comes from the fact that you assigned it incorrectly.
The second parameter to this function is the index of the block you are assigning a binding index to. The only way to get a correct index is to query it via Program Introspection APIs. The block index is the resource index, queried through this call:
auto block_index = glGetProgramResourceIndex​(test_prog, GL_SHADER_STORAGE_BLOCK, "A_SSB");
It just so happened, in your original code, that the shader compiler assigned A_SSB's resource index to 0 and B_SSB's resource index to 1. This assignment was probably arbitrarily done based on their names. Thus, when you changed the names on them, the resource indices didn't change. So A_SSB was still resource index 0, but your shader assigned it binding index 1. Which was fine...
Until your C++ code overrode that assignment with your glShaderStorageBlockBinding(test_prog, 0, 0). That assigned resource index 0 (A_SSB) to binding index 0.
You should either set the binding index in the shader or in C++ code. Not in both.