From e90e147cbc0cbc8dcf48000e15190badf75250f4 Mon Sep 17 00:00:00 2001 From: Denys Vlasenko Date: Thu, 26 Feb 2015 14:40:28 -0800 Subject: x86/asm/entry/64: Fix comments - Misleading and slightly incorrect comments in "struct pt_regs" are fixed (four instances). - Fix incorrect comment atop EMPTY_FRAME macro. - Explain in more detail what we do with stack layout during hw interrupt. - Correct comments about "partial stack frame" which are no longer true. Signed-off-by: Denys Vlasenko Signed-off-by: Andy Lutomirski Cc: Alexei Starovoitov Cc: Borislav Petkov Cc: Frederic Weisbecker Cc: H. Peter Anvin Cc: Kees Cook Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Will Drewry Link: http://lkml.kernel.org/r/1423778052-21038-3-git-send-email-dvlasenk@redhat.com Link: http://lkml.kernel.org/r/e1f4429c491fe6ceeddb879dea2786e0f8920f9c.1424989793.git.luto@amacapital.net Signed-off-by: Ingo Molnar --- arch/x86/kernel/entry_64.S | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) (limited to 'arch/x86/kernel') diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index e8372e08f8c2..695f4d434a84 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -14,9 +14,6 @@ * NOTE: This code handles signal-recognition, which happens every time * after an interrupt and after each system call. * - * Normal syscalls and interrupts don't save a full stack frame, this is - * only done for syscall tracing, signals or fork/exec et.al. - * * A note on terminology: * - top of stack: Architecture defined interrupt frame from SS to RIP * at the top of the kernel process stack. @@ -151,7 +148,7 @@ ENDPROC(native_usergs_sysret64) .endm /* - * initial frame state for interrupts (and exceptions without error code) + * empty frame */ .macro EMPTY_FRAME start=1 offset=0 .if \start @@ -379,7 +376,7 @@ tracesys_phase2: call syscall_trace_enter_phase2 /* - * Reload arg registers from stack in case ptrace changed them. + * Reload registers from stack in case ptrace changed them. * We don't reload %rax because syscall_trace_entry_phase2() returned * the value it wants us to use in the table lookup. */ @@ -629,6 +626,13 @@ END(interrupt) /* 0(%rsp): ~(interrupt number) */ .macro interrupt func cld + /* + * Since nothing in interrupt handling code touches r12...r15 members + * of "struct pt_regs", and since interrupts can nest, we can save + * four stack slots and simultaneously provide + * an unwind-friendly stack layout by saving "truncated" pt_regs + * exactly up to rbp slot, without these members. + */ ALLOC_PT_GPREGS_ON_STACK -RBP SAVE_C_REGS -RBP /* this goes to 0(%rsp) for unwinder, not for saving the value: */ @@ -641,6 +645,7 @@ END(interrupt) SWAPGS 1: /* + * Save previous stack pointer, optionally switch to interrupt stack. * irq_count is used to check if a CPU is already on an interrupt stack * or not. While this is essentially redundant with preempt_count it is * a little cheaper to use a separate counter in the PDA (short of @@ -681,6 +686,7 @@ ret_from_intr: /* Restore saved previous stack */ popq %rsi CFI_DEF_CFA rsi,SS+8-RBP /* reg/off reset after def_cfa_expr */ + /* return code expects complete pt_regs - adjust rsp accordingly: */ leaq ARGOFFSET-RBP(%rsi), %rsp CFI_DEF_CFA_REGISTER rsp CFI_ADJUST_CFA_OFFSET RBP-ARGOFFSET @@ -692,7 +698,7 @@ exit_intr: /* Interrupt came from user space */ /* - * Has a correct top of stack, but a partial stack frame + * Has a correct top of stack. * %rcx: thread info. Interrupts off. */ retint_with_reschedule: -- cgit