arch/x86/kernel/step.c

Source file repositories/reference/linux-study-clean/arch/x86/kernel/step.c

File Facts

System
Linux kernel
Corpus path
arch/x86/kernel/step.c
Extension
.c
Size
6426 bytes
Lines
245
Domain
Architecture Layer
Bucket
arch/x86
Inferred role
Architecture Layer: implementation source
Status
source implementation candidate

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

Dependency Surface

Detected Declarations

Annotated Snippet

switch (opcode[i]) {
		/* popf and iret */
		case 0x9d: case 0xcf:
			return 1;

			/* CHECKME: 64 65 */

		/* opcode and address size prefixes */
		case 0x66: case 0x67:
			continue;
		/* irrelevant prefixes (segment overrides and repeats) */
		case 0x26: case 0x2e:
		case 0x36: case 0x3e:
		case 0x64: case 0x65:
		case 0xf0: case 0xf2: case 0xf3:
			continue;

#ifdef CONFIG_X86_64
		case 0x40 ... 0x4f:
			if (!user_64bit_mode(regs))
				/* 32-bit mode: register increment */
				return 0;
			/* 64-bit mode: REX prefix */
			continue;
#endif

			/* CHECKME: f2, f3 */

		/*
		 * pushf: NOTE! We should probably not let
		 * the user see the TF bit being set. But
		 * it's more pain than it's worth to avoid
		 * it, and a debugger could emulate this
		 * all in user space if it _really_ cares.
		 */
		case 0x9c:
		default:
			return 0;
		}
	}
	return 0;
}

/*
 * Enable single-stepping.  Return nonzero if user mode is not using TF itself.
 */
static int enable_single_step(struct task_struct *child)
{
	struct pt_regs *regs = task_pt_regs(child);
	unsigned long oflags;

	/*
	 * If we stepped into a sysenter/syscall insn, it trapped in
	 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
	 * If user-mode had set TF itself, then it's still clear from
	 * do_debug() and we need to set it again to restore the user
	 * state so we don't wrongly set TIF_FORCED_TF below.
	 * If enable_single_step() was used last and that is what
	 * set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are
	 * already set and our bookkeeping is fine.
	 */
	if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP)))
		regs->flags |= X86_EFLAGS_TF;

	/*
	 * Always set TIF_SINGLESTEP.  This will also
	 * cause us to set TF when returning to user mode.
	 */
	set_tsk_thread_flag(child, TIF_SINGLESTEP);

	/*
	 * Ensure that a trap is triggered once stepping out of a system
	 * call prior to executing any user instruction.
	 */
	set_task_syscall_work(child, SYSCALL_EXIT_TRAP);

	oflags = regs->flags;

	/* Set TF on the kernel stack.. */
	regs->flags |= X86_EFLAGS_TF;

	/*
	 * ..but if TF is changed by the instruction we will trace,
	 * don't mark it as being "us" that set it, so that we
	 * won't clear it by hand later.
	 *
	 * Note that if we don't actually execute the popf because
	 * of a signal arriving right now or suchlike, we will lose
	 * track of the fact that it really was "us" that set it.
	 */

Annotation

Implementation Notes