How linker place symbols in a memory section

Question

I'm trying to figuring out how memory layout is generated by linker. I have basic knowledge about memory sections and their attributes. My question is how linker place symbols inside a specific section?

For example; a C-like array elements are guaranteed to place consecutively in the data section.

+---------+
|   A[0]  | 0x0000 <- An arbitrary memory address
+---------+
|   A[1]  | 0x0004
+---------+
|   A[2]  | 0x0008
+---------+
|         |
|   ...   |
|         |
+---------+

Apart from the local variables that placed in stack, how other variables are placed by the linker?

Let's assume I have two separate module foo and bar, and all of their variables will be placed to the memory without discarding by optimizations.

Module foo:
    var a;
    var b;


Module bar:
    var a;
    var b;

Is there any rule or convention for this case such as; same module variables are placed consecutively or symbol names generated by the compiler are placed alphabetically?

+-----------+
|   a(foo)  | \ 
+-----------+  -> Same module variables placed consecutively
|   b(foo)  | /
+-----------+
|   a(bar)  | \
+-----------+  -> Same module variables placed consecutively
|   b(bar)  | /
+-----------+
|           |
|    ...    |
|           |
+-----------+


+-----------+
|   a(foo)  | \ 
+-----------+  -> Variables placed alphabetically
|   a(bar)  | /
+-----------+
|   b(foo)  | \
+-----------+  -> Variables placed alphabetically
|   b(bar)  | /
+-----------+
|           |
|    ...    |
|           |
+-----------+

I've checked both GCC and LLVM documentations but couldn't find any information about this topic. Is there any place where I can look for more detailed information about address assignments or memory layout optimizations?