It does hide some assembly. Those calls are calling an assembler to generate native code at runtime for JIT compilation. The C++ compiler compiles an assembler, but this assembler runs at runtime. `MacroAssembler` itself is architecture independent, and calls into functions implemented in back-ends such as `MacroAssemblerARM` and `MacroAssemblerX64`.

So the code in this function is not performing the stack-probing, it generates code to perform it instead.