On Sun, Feb 18, 2018 at 01:31:16PM +0100, Dominik Brodowski wrote:
> Open-code the two instances which used switch_to_thread_stack. This
> allows us to remove the wrapper around DO_SWITCH_TO_THREAD_STACK.
> While at it, update the UNWIND hint to reflect where the IRET frame is.
> Signed-off-by: Dominik Brodowski <li...@dominikbrodowski.net>
> arch/x86/entry/entry_64.S | 59
> arch/x86/entry/entry_64_compat.S | 19 ++++++++++++-
> 2 files changed, 42 insertions(+), 36 deletions(-)
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 0ac2b4865d58..fa61be457082 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -539,17 +539,36 @@ END(irq_entries_start)
> - * Switch to the thread stack. This is called with the IRET frame and
> - * orig_ax on the stack. (That is, RDI..R12 are not on the stack and
> - * space has not been allocated for them.)
> + * Interrupt entry/exit.
> + *
> + * Interrupt entry points save only callee clobbered registers in fast path.
> + *
> + * Entry runs with interrupts off.
These comments aren't really accurate anymore:
- The function only handles interrupt entry, not exit.
- All registers are saved, there is no fast path.
> -.macro DO_SWITCH_TO_THREAD_STACK
> +/* 8(%rsp): ~(interrupt number) */
"interrupt_helper" is a bit vague, how about "interrupt_entry"? That
better describes its purpose and also makes it more analagous to
paranoid_entry() and error_entry().
> + UNWIND_HINT_FUNC
> + cld
> + testb $3, CS-ORIG_RAX+8(%rsp)
> + jz 1f
> + SWAPGS
> + /*
> + * Switch to the thread stack. The IRET frame and orig_ax are
> + * on the stack, as well as the return address. RDI..R12 are
> + * not (yet) on the stack and space has not (yet) been
> + * allocated for them.
> + */
> pushq %rdi
> /* Need to switch before accessing the thread stack. */
> SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
> movq %rsp, %rdi
> movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
> - UNWIND_HINT sp_offset=16 sp_reg=ORC_REG_DI
> + /* We have RDI, return address, and orig_ax on the stack on
> + * top of the IRET frame. That means offset=24 */
> + UNWIND_HINT_IRET_REGS base=%rdi offset=24
The hint looks right, though the comment formatting isn't in the kernel
> diff --git a/arch/x86/entry/entry_64_compat.S
> index 364ea4a207be..5b9503c7148d 100644
> --- a/arch/x86/entry/entry_64_compat.S
> +++ b/arch/x86/entry/entry_64_compat.S
> @@ -350,7 +350,24 @@ ENTRY(entry_INT80_compat)
> pushq %rax /* pt_regs->orig_ax */
> /* switch to thread stack expects orig_ax to be pushed */
> - call switch_to_thread_stack
> + pushq %rdi
> + /* Need to switch before accessing the thread stack. */
> + SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
> + movq %rsp, %rdi
> + movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
> + /* We have RDI and orig_ax on the stack on top of the IRET frame.
> + * That means offset=16 */
> + UNWIND_HINT_IRET_REGS base=%rdi offset=16
Objtool doesn't scan this file yet, so no hints needed here yet.
Adding it to my TODO list...