arch/powerpc/lib/test_emulate_step_exec_instr.S

Source file repositories/reference/linux-study-clean/arch/powerpc/lib/test_emulate_step_exec_instr.S

File Facts

System
Linux kernel
Corpus path
arch/powerpc/lib/test_emulate_step_exec_instr.S
Extension
.S
Size
3507 bytes
Lines
151
Domain
Architecture Layer
Bucket
arch/powerpc
Inferred role
Architecture Layer: arch/powerpc
Status
atlas-only

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

#include <asm/asm-offsets.h>
#include <asm/ppc_asm.h>
#include <asm/code-patching-asm.h>
#include <linux/errno.h>

/* int exec_instr(struct pt_regs *regs) */
_GLOBAL(exec_instr)

	/*
	 * Stack frame layout (INT_FRAME_SIZE bytes)
	 *   In-memory pt_regs	(SP + STACK_INT_FRAME_REGS)
	 *   Scratch space	(SP + 8)
	 *   Back chain		(SP + 0)
	 */

	/*
	 * Allocate a new stack frame with enough space to hold the register
	 * states in an in-memory pt_regs and also create the back chain to
	 * the caller's stack frame.
	 */
	stdu	r1, -INT_FRAME_SIZE(r1)

	/*
	 * Save non-volatile GPRs on stack. This includes TOC pointer (GPR2)
	 * and local variables (GPR14 to GPR31). The register for the pt_regs
	 * parameter (GPR3) is saved additionally to ensure that the resulting
	 * register state can still be saved even if GPR3 gets overwritten
	 * when loading the initial register state for the test instruction.
	 * The stack pointer (GPR1) and the thread pointer (GPR13) are not
	 * saved as these should not be modified anyway.
	 */
	SAVE_GPRS(2, 3, r1)
	SAVE_NVGPRS(r1)

	/*
	 * Save LR on stack to ensure that the return address is available
	 * even if it gets overwritten by the test instruction.
	 */
	mflr	r0
	std	r0, _LINK(r1)

	/*
	 * Save CR on stack. For simplicity, the entire register is saved
	 * even though only fields 2 to 4 are non-volatile.
	 */
	mfcr	r0
	std	r0, _CCR(r1)

	/*
	 * Load register state for the test instruction without touching the
	 * critical non-volatile registers. The register state is passed as a
	 * pointer to a pt_regs instance.
	 */
	subi	r31, r3, GPR0

	/* Load LR from pt_regs */
	ld	r0, _LINK(r31)
	mtlr	r0

	/* Load CR from pt_regs */
	ld	r0, _CCR(r31)
	mtcr	r0

	/* Load XER from pt_regs */
	ld	r0, _XER(r31)
	mtxer	r0

	/* Load GPRs from pt_regs */
	REST_GPR(0, r31)
	REST_GPRS(2, 12, r31)

Annotation

Implementation Notes