bpf, x86: Support unwind_goto and unwind_exit

  bpf                         x86
  call inner                  call inner
  unwind_goto pad
  w0 = w6                     mov eax, ebx

  r0 = 0                      xor eax, eax
  unwind_exit                 push rax
                              push rsi
                              mov rdi, [rbp + 8]
                              call bpf_unwind_target
                              mov [rbp + 8], rax
                              pop rsi
                              pop rax
                              leave
                              ret

unwind_goto is an extable entry and no code. unwind_exit looks its return
address up there and returns to the pad. r0 and r2 are what a subprog
returns, so rax and rsi are saved around the lookup.

When there is no entry, the kernel called the subprog as an async or an
exception callback, and unwind_exit is exit.

The caller of the main prog doesn't tell exit from unwind_exit, so there
it's exit. An extension is different. freplace is a jump, so its return
address is the one of the subprog that it replaced.

With private stack r9 is saved around a call, and 'pop r9' has to be done
on the way to the pad too. In such progs unwind_goto is:

  push r9
  call foo
  pop r9       <- exit returns here
  jmp 1f
  pop r9       <- unwind_exit returns here
  jmp pad
1:

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://patch.msgid.link/20261020181320.1284798-3-alexei.starovoitov@gmail.com

0 files changed, 0 insertions, 0 deletions