On intel platforms, BP is used to point to the beginning of the stack frame and to access the arguments [bp+0x??] and local variables [bp-0x??]
BP
[bp+0x??]
[bp-0x??]
What you are looking for is the Frame Pointer. Generally, R7 acts as the frame pointer in THUMB mode and R11 acts as the frame pointer in ARM mode. But it is under the discretion of the OS to change this convention if it wishes to.
R7
R11
Read here