arch/powerpc/kernel/ftrace.c

/*
 * Code for replacing ftrace calls with jumps.
 *
 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
 *
 * Thanks goes out to P.A. Semi, Inc for supplying me with a PPC64 box.
 *
 */

#include <linux/spinlock.h>
#include <linux/hardirq.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/ftrace.h>
#include <linux/percpu.h>
#include <linux/init.h>
#include <linux/list.h>

#include <asm/cacheflush.h>
#include <asm/code-patching.h>
#include <asm/ftrace.h>

#if 0
#define DEBUGP printk
#else
#define DEBUGP(fmt , ...)	do { } while (0)
#endif

static unsigned int ftrace_nop = PPC_NOP_INSTR;

#ifdef CONFIG_PPC32
# define GET_ADDR(addr) addr
#else
/* PowerPC64's functions are data that points to the functions */
# define GET_ADDR(addr) (*(unsigned long *)addr)
#endif


static unsigned int ftrace_calc_offset(long ip, long addr)
{
	return (int)(addr - ip);
}

static unsigned char *ftrace_nop_replace(void)
{
	return (char *)&ftrace_nop;
}

static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
{
	static unsigned int op;

	/*
	 * It would be nice to just use create_function_call, but that will
	 * update the code itself. Here we need to just return the
	 * instruction that is going to be modified, without modifying the
	 * code.
	 */
	addr = GET_ADDR(addr);

	/* Set to "bl addr" */
	op = 0x48000001 | (ftrace_calc_offset(ip, addr) & 0x03fffffc);

	/*
	 * No locking needed, this must be called via kstop_machine
	 * which in essence is like running on a uniprocessor machine.
	 */
	return (unsigned char *)&op;
}

#ifdef CONFIG_PPC64
# define _ASM_ALIGN	" .align 3 "
# define _ASM_PTR	" .llong "
#else
# define _ASM_ALIGN	" .align 2 "
# define _ASM_PTR	" .long "
#endif

static int
ftrace_modify_code(unsigned long ip, unsigned char *old_code,
		   unsigned char *new_code)
{
	unsigned char replaced[MCOUNT_INSN_SIZE];

	/*
	 * Note: Due to modules and __init, code can
	 *  disappear and change, we need to protect against faulting
	 *  as well as code changing. We do this by using the
	 *  probe_kernel_* functions.
	 *
	 * No real locking needed, this code is run through
	 * kstop_machine, or before SMP starts.
	 */

	/* read the text we want to modify */
	if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
		return -EFAULT;

	/* Make sure it is what we expect it to be */
	if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
		return -EINVAL;

	/* replace the text with the new text */
	if (probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE))
		return -EPERM;

	flush_icache_range(ip, ip + 8);

	return 0;
}

/*
 * Helper functions that are the same for both PPC64 and PPC32.
 */
static int test_24bit_addr(unsigned long ip, unsigned long addr)
{
	long diff;

	/*
	 * Can we get to addr from ip in 24 bits?
	 *  (26 really, since we mulitply by 4 for 4 byte alignment)
	 */
	diff = addr - ip;

	/*
	 * Return true if diff is less than 1 << 25
	 *  and greater than -1 << 26.
	 */
	return (diff < (1 << 25)) && (diff > (-1 << 26));
}

static int is_bl_op(unsigned int op)
{
	return (op & 0xfc000003) == 0x48000001;
}

static int test_offset(unsigned long offset)
{
	return (offset + 0x2000000 > 0x3ffffff) || ((offset & 3) != 0);
}

static unsigned long find_bl_target(unsigned long ip, unsigned int op)
{
	static int offset;

	offset = (op & 0x03fffffc);
	/* make it signed */
	if (offset & 0x02000000)
		offset |= 0xfe000000;

	return ip + (long)offset;
}

static unsigned int branch_offset(unsigned long offset)
{
	/* return "bl ip+offset" */
	return 0x48000001 | (offset & 0x03fffffc);
}

#ifdef CONFIG_PPC64
static int
__ftrace_make_nop(struct module *mod,
		  struct dyn_ftrace *rec, unsigned long addr)
{
	unsigned char replaced[MCOUNT_INSN_SIZE * 2];
	unsigned int *op = (unsigned *)&replaced;
	unsigned char jmp[8];
	unsigned long *ptr = (unsigned long *)&jmp;
	unsigned long ip = rec->ip;
	unsigned long tramp;
	int offset;

	/* read where this goes */
	if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
		return -EFAULT;

	/* Make sure that that this is still a 24bit jump */
	if (!is_bl_op(*op)) {
		printk(KERN_ERR "Not expected bl: opcode is %x\n", *op);
		return -EINVAL;
	}

	/* lets find where the pointer goes */
	tramp = find_bl_target(ip, *op);

	/*
	 * On PPC64 the trampoline looks like:
	 * 0x3d, 0x82, 0x00, 0x00,    addis   r12,r2, <high>
	 * 0x39, 0x8c, 0x00, 0x00,    addi    r12,r12, <low>
	 *   Where the bytes 2,3,6 and 7 make up the 32bit offset
	 *   to the TOC that holds the pointer.
	 *   to jump to.
	 * 0xf8, 0x41, 0x00, 0x28,    std     r2,40(r1)
	 * 0xe9, 0x6c, 0x00, 0x20,    ld      r11,32(r12)
	 *   The actually address is 32 bytes from the offset
	 *   into the TOC.
	 * 0xe8, 0x4c, 0x00, 0x28,    ld      r2,40(r12)
	 */

	DEBUGP("ip:%lx jumps to %lx r2: %lx", ip, tramp, mod->arch.toc);

	/* Find where the trampoline jumps to */
	if (probe_kernel_read(jmp, (void *)tramp, 8)) {
		printk(KERN_ERR "Failed to read %lx\n", tramp);
		return -EFAULT;
	}

	DEBUGP(" %08x %08x",
	       (unsigned)(*ptr >> 32),
	       (unsigned)*ptr);

	offset = (unsigned)jmp[2] << 24 |
		(unsigned)jmp[3] << 16 |
		(unsigned)jmp[6] << 8 |
		(unsigned)jmp[7];

	DEBUGP(" %x ", offset);

	/* get the address this jumps too */
	tramp = mod->arch.toc + offset + 32;
	DEBUGP("toc: %lx", tramp);

	if (probe_kernel_read(jmp, (void *)tramp, 8)) {
		printk(KERN_ERR "Failed to read %lx\n", tramp);
		return -EFAULT;
	}

	DEBUGP(" %08x %08x\n",
	       (unsigned)(*ptr >> 32),
	       (unsigned)*ptr);

	/* This should match what was called */
	if (*ptr != GET_ADDR(addr)) {
		printk(KERN_ERR "addr does not match %lx\n", *ptr);
		return -EINVAL;
	}

	/*
	 * We want to nop the line, but the next line is
	 *  0xe8, 0x41, 0x00, 0x28   ld r2,40(r1)
	 * This needs to be turned to a nop too.
	 */
	if (probe_kernel_read(replaced, (void *)(ip+4), MCOUNT_INSN_SIZE))
		return -EFAULT;

	if (*op != 0xe8410028) {
		printk(KERN_ERR "Next line is not ld! (%08x)\n", *op);
		return -EINVAL;
	}

	/*
	 * Milton Miller pointed out that we can not blindly do nops.
	 * If a task was preempted when calling a trace function,
	 * the nops will remove the way to restore the TOC in r2
	 * and the r2 TOC will get corrupted.
	 */

	/*
	 * Replace:
	 *   bl <tramp>  <==== will be replaced with "b 1f"
	 *   ld r2,40(r1)
	 *  1:
	 */
	op[0] = 0x48000008;	/* b +8 */

	if (probe_kernel_write((void *)ip, replaced, MCOUNT_INSN_SIZE))
		return -EPERM;

	return 0;
}

#else /* !PPC64 */
static int
__ftrace_make_nop(struct module *mod,
		  struct dyn_ftrace *rec, unsigned long addr)
{
	/* Ignore modules for PPC32 (for now) */
	return 0;
}
#endif /* PPC64 */

int ftrace_make_nop(struct module *mod,
		    struct dyn_ftrace *rec, unsigned long addr)
{
	unsigned char *old, *new;
	unsigned long ip = rec->ip;

	/*
	 * If the calling address is more that 24 bits away,
	 * then we had to use a trampoline to make the call.
	 * Otherwise just update the call site.
	 */
	if (test_24bit_addr(ip, addr)) {
		/* within range */
		old = ftrace_call_replace(ip, addr);
		new = ftrace_nop_replace();
		return ftrace_modify_code(ip, old, new);
	}

#ifdef CONFIG_PPC64
	/*
	 * Out of range jumps are called from modules.
	 * We should either already have a pointer to the module
	 * or it has been passed in.
	 */
	if (!rec->arch.mod) {
		if (!mod) {
			printk(KERN_ERR "No module loaded addr=%lx\n",
			       addr);
			return -EFAULT;
		}
		rec->arch.mod = mod;
	} else if (mod) {
		if (mod != rec->arch.mod) {
			printk(KERN_ERR
			       "Record mod %p not equal to passed in mod %p\n",
			       rec->arch.mod, mod);
			return -EINVAL;
		}
		/* nothing to do if mod == rec->arch.mod */
	} else
		mod = rec->arch.mod;
#endif /* CONFIG_PPC64 */

	return __ftrace_make_nop(mod, rec, addr);

}

#ifdef CONFIG_PPC64
static int
__ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
	unsigned char replaced[MCOUNT_INSN_SIZE * 2];
	unsigned int *op = (unsigned *)&replaced;
	unsigned long ip = rec->ip;
	unsigned long offset;

	/* read where this goes */
	if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE * 2))
		return -EFAULT;

	/*
	 * It should be pointing to two nops or
	 *  b +8; ld r2,40(r1)
	 */
	if (((op[0] != 0x48000008) || (op[1] != 0xe8410028)) &&
	    ((op[0] != PPC_NOP_INSTR) || (op[1] != PPC_NOP_INSTR))) {
		printk(KERN_ERR "Expected NOPs but have %x %x\n", op[0], op[1]);
		return -EINVAL;
	}

	/* If we never set up a trampoline to ftrace_caller, then bail */
	if (!rec->arch.mod->arch.tramp) {
		printk(KERN_ERR "No ftrace trampoline\n");
		return -EINVAL;
	}

	/* now calculate a jump to the ftrace caller trampoline */
	offset = rec->arch.mod->arch.tramp - ip;

	if (test_offset(offset)) {
		printk(KERN_ERR "REL24 %li out of range!\n",
		       (long int)offset);
		return -EINVAL;
	}

	/* Set to "bl addr" */
	op[0] = branch_offset(offset);
	/* ld r2,40(r1) */
	op[1] = 0xe8410028;

	DEBUGP("write to %lx\n", rec->ip);

	if (probe_kernel_write((void *)ip, replaced, MCOUNT_INSN_SIZE * 2))
		return -EPERM;

	return 0;
}
#else
static int
__ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
	/* PPC32 ignores modules for now */
	return 0;
}
#endif /* CONFIG_PPC64 */

int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
	unsigned char *old, *new;
	unsigned long ip = rec->ip;

	/*
	 * If the calling address is more that 24 bits away,
	 * then we had to use a trampoline to make the call.
	 * Otherwise just update the call site.
	 */
	if (test_24bit_addr(ip, addr)) {
		/* within range */
		old = ftrace_nop_replace();
		new = ftrace_call_replace(ip, addr);
		return ftrace_modify_code(ip, old, new);
	}

#ifdef CONFIG_PPC64
	/*
	 * Out of range jumps are called from modules.
	 * Being that we are converting from nop, it had better
	 * already have a module defined.
	 */
	if (!rec->arch.mod) {
		printk(KERN_ERR "No module loaded\n");
		return -EINVAL;
	}
#endif

	return __ftrace_make_call(rec, addr);
}

int ftrace_update_ftrace_func(ftrace_func_t func)
{
	unsigned long ip = (unsigned long)(&ftrace_call);
	unsigned char old[MCOUNT_INSN_SIZE], *new;
	int ret;

	memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE);
	new = ftrace_call_replace(ip, (unsigned long)func);
	ret = ftrace_modify_code(ip, old, new);

	return ret;
}

int __init ftrace_dyn_arch_init(void *data)
{
	/* caller expects data to be zero */
	unsigned long *p = data;

	*p = 0;

	return 0;
}