The _switch stack frame setup are substantially the same, so are the
comments. The difference in how the stack and current are switched,
and other hardware and software housekeeping is done is moved into
macros.

Generated code should be unchanged.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Tweak include orer to fix compile errors on some configs]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230606132447.315714-6-npiggin@gmail.com

Change the order of some operations and change some register numbers in
preparation to merge 32-bit and 64-bit switch.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230606132447.315714-5-npiggin@gmail.com

64-bit has removed the sync from _switch since commit 9145effd626d1
("powerpc/64: Drop explicit hwsync in context switch"). The same
logic there should apply to 32-bit. Remove the sync and replace with
a placeholder comment (32 and 64 will be merged with a later change).

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230606132447.315714-4-npiggin@gmail.com

Kernel created user threads start similarly to kernel threads in that
they call a kernel function after first returning from _switch, so
they share ret_from_kernel_thread for this. Kernel threads never return
from that function though, whereas user threads often do (although some
don't, e.g., IO threads).

Split these startup functions in two, and catch kernel threads that
improperly return from their function. This is intended to make the
complicated code a little bit easier to understand.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230325122904.2375060-7-npiggin@gmail.com

The kernel thread path in copy_thread creates a user interrupt frame on
stack and stores the function and arg parameters there, and
ret_from_kernel_thread loads them. This is a slightly confusing way to
overload that frame. Non-volatile registers are loaded from the switch
frame, so the parameters can be stored there. The user interrupt frame
is now only used by user threads when they return to user.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230325122904.2375060-4-npiggin@gmail.com

The ret_from_fork code for 64e and 32-bit set r3 for
syscall_exit_prepare the same way that 64s does, so there should
be no need to special-case them in copy_thread.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230325122904.2375060-3-npiggin@gmail.com

Merge the powerpc objtool support, which we were keeping in a topic
branch in case of any merge conflicts.

This is open-coded in process.c, ppc32 uses a different define with the
same value, and the C definition is name differently which makes it an
extra indirection to grep for.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221127124942.1665522-12-npiggin@gmail.com

Define a constant rather than open-code the offset for the
"regs" marker.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221127124942.1665522-9-npiggin@gmail.com

This is a common offset that currently uses the overloaded
STACK_FRAME_OVERHEAD constant. It's easier to read and more
flexible to use a specific regs offset for this.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221127124942.1665522-8-npiggin@gmail.com