[parisc-linux] Questions understanding exec_kernel
Wed, 22 Sep 1999 15:29:37 +0200
> * exec_kernel(entry_point, &commandline, Kernel_FreeMemStart,
> half_bss_size );
> * exec_kernel() calls our kernel...
> .EXPORT exec_kernel,code
> mtsm %r0 ; Disable traps and interrupts.
> mtctl %r0, %cr17 ; Clear two-level IIA Space Queue
> mtctl %r0, %cr17 ; effectively setting kernel space.
> [Question: Page 5-149 from the PA-RISC 1.1 Architecture and Instruction
> Set Reference Manual states: "Level 0: If the target control register
> is CR 8, 9, 12, 13, 17, or 20, this instructin executes as a null
> instruction." I am assuming we are running at level 0 since the rfi
> command required running at level 0, so what is the difference between a
> null instruction and a nop?]
Level 0 refers to the hardware here. Level 0 hardware basically has no MMU,
so Linux will never run on it (does HP/UX ?)
> copy %arg2, %arg0 ; commandline to arg1
> [Note: I think the comment is incorrect... we are actually copying the
> Kernel_FreeMemStart into arg0 ... Am I missunderstanding the comment?]
No, looks like the comment did not get changed when the instruction did.
> ; arg3 is not changed..
> rfi ; begin execution of kernel.
> [Question: Page 5-139 from the PA-RISC 1.1 Architecture and Instruction
> Set Reference Manual states: "Execution of an RFI instruction when any
> of the PSW !, I, or R bits are ones is an undefined operation." We are
> explicitly setting the Q & I bits before calling the rfi command. I
> don't understand how this works ... ]
We did execute mtsm 0 which sets the system mask (which includes the Q, I and
R bits) to 0.