csum_partial.s

linux 内核源代码

#define STREST  STOREL
#define SHIFT_DISCARD SLLV
#define SHIFT_DISCARD_REVERT SRLV
#else
#define LDFIRST LOADL
#define LDREST  LOADR
#define STFIRST STOREL
#define STREST  STORER
#define SHIFT_DISCARD SRLV
#define SHIFT_DISCARD_REVERT SLLV
#endif

#define FIRST(unit) ((unit)*NBYTES)
#define REST(unit)  (FIRST(unit)+NBYTES-1)

#define ADDRMASK (NBYTES-1)

	.set	noat

LEAF(__csum_partial_copy_user)
	PTR_ADDU	AT, src, len	/* See (1) above. */
#ifdef CONFIG_64BIT
	move	errptr, a4
#else
	lw	errptr, 16(sp)
#endif
FEXPORT(csum_partial_copy_nocheck)
	move	sum, zero
	move	odd, zero
	/*
	 * Note: dst & src may be unaligned, len may be 0
	 * Temps
	 */
	/*
	 * The "issue break"s below are very approximate.
	 * Issue delays for dcache fills will perturb the schedule, as will
	 * load queue full replay traps, etc.
	 *
	 * If len < NBYTES use byte operations.
	 */
	sltu	t2, len, NBYTES
	and	t1, dst, ADDRMASK
	bnez	t2, copy_bytes_checklen
	 and	t0, src, ADDRMASK
	andi	odd, dst, 0x1			/* odd buffer? */
	bnez	t1, dst_unaligned
	 nop
	bnez	t0, src_unaligned_dst_aligned
	/*
	 * use delay slot for fall-through
	 * src and dst are aligned; need to compute rem
	 */
both_aligned:
	 SRL	t0, len, LOG_NBYTES+3    # +3 for 8 units/iter
	beqz	t0, cleanup_both_aligned # len < 8*NBYTES
	 nop
	SUB	len, 8*NBYTES		# subtract here for bgez loop
	.align	4
1:
EXC(	LOAD	t0, UNIT(0)(src),	l_exc)
EXC(	LOAD	t1, UNIT(1)(src),	l_exc_copy)
EXC(	LOAD	t2, UNIT(2)(src),	l_exc_copy)
EXC(	LOAD	t3, UNIT(3)(src),	l_exc_copy)
EXC(	LOAD	t4, UNIT(4)(src),	l_exc_copy)
EXC(	LOAD	t5, UNIT(5)(src),	l_exc_copy)
EXC(	LOAD	t6, UNIT(6)(src),	l_exc_copy)
EXC(	LOAD	t7, UNIT(7)(src),	l_exc_copy)
	SUB	len, len, 8*NBYTES
	ADD	src, src, 8*NBYTES
EXC(	STORE	t0, UNIT(0)(dst),	s_exc)
	ADDC(sum, t0)
EXC(	STORE	t1, UNIT(1)(dst),	s_exc)
	ADDC(sum, t1)
EXC(	STORE	t2, UNIT(2)(dst),	s_exc)
	ADDC(sum, t2)
EXC(	STORE	t3, UNIT(3)(dst),	s_exc)
	ADDC(sum, t3)
EXC(	STORE	t4, UNIT(4)(dst),	s_exc)
	ADDC(sum, t4)
EXC(	STORE	t5, UNIT(5)(dst),	s_exc)
	ADDC(sum, t5)
EXC(	STORE	t6, UNIT(6)(dst),	s_exc)
	ADDC(sum, t6)
EXC(	STORE	t7, UNIT(7)(dst),	s_exc)
	ADDC(sum, t7)
	bgez	len, 1b
	 ADD	dst, dst, 8*NBYTES
	ADD	len, 8*NBYTES		# revert len (see above)

	/*
	 * len == the number of bytes left to copy < 8*NBYTES
	 */
cleanup_both_aligned:
#define rem t7
	beqz	len, done
	 sltu	t0, len, 4*NBYTES
	bnez	t0, less_than_4units
	 and	rem, len, (NBYTES-1)	# rem = len % NBYTES
	/*
	 * len >= 4*NBYTES
	 */
EXC(	LOAD	t0, UNIT(0)(src),	l_exc)
EXC(	LOAD	t1, UNIT(1)(src),	l_exc_copy)
EXC(	LOAD	t2, UNIT(2)(src),	l_exc_copy)
EXC(	LOAD	t3, UNIT(3)(src),	l_exc_copy)
	SUB	len, len, 4*NBYTES
	ADD	src, src, 4*NBYTES
EXC(	STORE	t0, UNIT(0)(dst),	s_exc)
	ADDC(sum, t0)
EXC(	STORE	t1, UNIT(1)(dst),	s_exc)
	ADDC(sum, t1)
EXC(	STORE	t2, UNIT(2)(dst),	s_exc)
	ADDC(sum, t2)
EXC(	STORE	t3, UNIT(3)(dst),	s_exc)
	ADDC(sum, t3)
	beqz	len, done
	 ADD	dst, dst, 4*NBYTES
less_than_4units:
	/*
	 * rem = len % NBYTES
	 */
	beq	rem, len, copy_bytes
	 nop
1:
EXC(	LOAD	t0, 0(src),		l_exc)
	ADD	src, src, NBYTES
	SUB	len, len, NBYTES
EXC(	STORE	t0, 0(dst),		s_exc)
	ADDC(sum, t0)
	bne	rem, len, 1b
	 ADD	dst, dst, NBYTES

	/*
	 * src and dst are aligned, need to copy rem bytes (rem < NBYTES)
	 * A loop would do only a byte at a time with possible branch
	 * mispredicts.  Can't do an explicit LOAD dst,mask,or,STORE
	 * because can't assume read-access to dst.  Instead, use
	 * STREST dst, which doesn't require read access to dst.
	 *
	 * This code should perform better than a simple loop on modern,
	 * wide-issue mips processors because the code has fewer branches and
	 * more instruction-level parallelism.
	 */
#define bits t2
	beqz	len, done
	 ADD	t1, dst, len	# t1 is just past last byte of dst
	li	bits, 8*NBYTES
	SLL	rem, len, 3	# rem = number of bits to keep
EXC(	LOAD	t0, 0(src),		l_exc)
	SUB	bits, bits, rem	# bits = number of bits to discard
	SHIFT_DISCARD t0, t0, bits
EXC(	STREST	t0, -1(t1),		s_exc)
	SHIFT_DISCARD_REVERT t0, t0, bits
	.set reorder
	ADDC(sum, t0)
	b	done
	.set noreorder
dst_unaligned:
	/*
	 * dst is unaligned
	 * t0 = src & ADDRMASK
	 * t1 = dst & ADDRMASK; T1 > 0
	 * len >= NBYTES
	 *
	 * Copy enough bytes to align dst
	 * Set match = (src and dst have same alignment)
	 */
#define match rem
EXC(	LDFIRST	t3, FIRST(0)(src),	l_exc)
	ADD	t2, zero, NBYTES
EXC(	LDREST	t3, REST(0)(src),	l_exc_copy)
	SUB	t2, t2, t1	# t2 = number of bytes copied
	xor	match, t0, t1
EXC(	STFIRST t3, FIRST(0)(dst),	s_exc)
	SLL	t4, t1, 3		# t4 = number of bits to discard
	SHIFT_DISCARD t3, t3, t4
	/* no SHIFT_DISCARD_REVERT to handle odd buffer properly */
	ADDC(sum, t3)
	beq	len, t2, done
	 SUB	len, len, t2
	ADD	dst, dst, t2
	beqz	match, both_aligned
	 ADD	src, src, t2

src_unaligned_dst_aligned:
	SRL	t0, len, LOG_NBYTES+2    # +2 for 4 units/iter
	beqz	t0, cleanup_src_unaligned
	 and	rem, len, (4*NBYTES-1)   # rem = len % 4*NBYTES
1:
/*
 * Avoid consecutive LD*'s to the same register since some mips
 * implementations can't issue them in the same cycle.
 * It's OK to load FIRST(N+1) before REST(N) because the two addresses
 * are to the same unit (unless src is aligned, but it's not).
 */
EXC(	LDFIRST	t0, FIRST(0)(src),	l_exc)
EXC(	LDFIRST	t1, FIRST(1)(src),	l_exc_copy)
	SUB     len, len, 4*NBYTES
EXC(	LDREST	t0, REST(0)(src),	l_exc_copy)
EXC(	LDREST	t1, REST(1)(src),	l_exc_copy)
EXC(	LDFIRST	t2, FIRST(2)(src),	l_exc_copy)
EXC(	LDFIRST	t3, FIRST(3)(src),	l_exc_copy)
EXC(	LDREST	t2, REST(2)(src),	l_exc_copy)
EXC(	LDREST	t3, REST(3)(src),	l_exc_copy)
	ADD	src, src, 4*NBYTES
#ifdef CONFIG_CPU_SB1
	nop				# improves slotting
#endif
EXC(	STORE	t0, UNIT(0)(dst),	s_exc)
	ADDC(sum, t0)
EXC(	STORE	t1, UNIT(1)(dst),	s_exc)
	ADDC(sum, t1)
EXC(	STORE	t2, UNIT(2)(dst),	s_exc)
	ADDC(sum, t2)
EXC(	STORE	t3, UNIT(3)(dst),	s_exc)
	ADDC(sum, t3)
	bne	len, rem, 1b
	 ADD	dst, dst, 4*NBYTES

cleanup_src_unaligned:
	beqz	len, done
	 and	rem, len, NBYTES-1  # rem = len % NBYTES
	beq	rem, len, copy_bytes
	 nop
1:
EXC(	LDFIRST t0, FIRST(0)(src),	l_exc)
EXC(	LDREST	t0, REST(0)(src),	l_exc_copy)
	ADD	src, src, NBYTES
	SUB	len, len, NBYTES
EXC(	STORE	t0, 0(dst),		s_exc)
	ADDC(sum, t0)
	bne	len, rem, 1b
	 ADD	dst, dst, NBYTES

copy_bytes_checklen:
	beqz	len, done
	 nop
copy_bytes:
	/* 0 < len < NBYTES  */
#ifdef CONFIG_CPU_LITTLE_ENDIAN
#define SHIFT_START 0
#define SHIFT_INC 8
#else
#define SHIFT_START 8*(NBYTES-1)
#define SHIFT_INC -8
#endif
	move	t2, zero	# partial word
	li	t3, SHIFT_START	# shift
/* use l_exc_copy here to return correct sum on fault */
#define COPY_BYTE(N)			\
EXC(	lbu	t0, N(src), l_exc_copy);	\
	SUB	len, len, 1;		\
EXC(	sb	t0, N(dst), s_exc);	\
	SLLV	t0, t0, t3;		\
	addu	t3, SHIFT_INC;		\
	beqz	len, copy_bytes_done;	\
	 or	t2, t0

	COPY_BYTE(0)
	COPY_BYTE(1)
#ifdef USE_DOUBLE
	COPY_BYTE(2)
	COPY_BYTE(3)
	COPY_BYTE(4)
	COPY_BYTE(5)
#endif
EXC(	lbu	t0, NBYTES-2(src), l_exc_copy)
	SUB	len, len, 1
EXC(	sb	t0, NBYTES-2(dst), s_exc)
	SLLV	t0, t0, t3
	or	t2, t0
copy_bytes_done:
	ADDC(sum, t2)
done:
	/* fold checksum */
#ifdef USE_DOUBLE
	dsll32	v1, sum, 0
	daddu	sum, v1
	sltu	v1, sum, v1
	dsra32	sum, sum, 0
	addu	sum, v1
#endif
	sll	v1, sum, 16
	addu	sum, v1
	sltu	v1, sum, v1
	srl	sum, sum, 16
	addu	sum, v1

	/* odd buffer alignment? */
	beqz	odd, 1f
	 nop
	sll	v1, sum, 8
	srl	sum, sum, 8
	or	sum, v1
	andi	sum, 0xffff
1:
	.set reorder
	ADDC(sum, psum)
	jr	ra
	.set noreorder

l_exc_copy:
	/*
	 * Copy bytes from src until faulting load address (or until a
	 * lb faults)
	 *
	 * When reached by a faulting LDFIRST/LDREST, THREAD_BUADDR($28)
	 * may be more than a byte beyond the last address.
	 * Hence, the lb below may get an exception.
	 *
	 * Assumes src < THREAD_BUADDR($28)
	 */
	LOAD	t0, TI_TASK($28)
	 li	t2, SHIFT_START
	LOAD	t0, THREAD_BUADDR(t0)
1:
EXC(	lbu	t1, 0(src),	l_exc)
	ADD	src, src, 1
	sb	t1, 0(dst)	# can't fault -- we're copy_from_user
	SLLV	t1, t1, t2
	addu	t2, SHIFT_INC
	ADDC(sum, t1)
	bne	src, t0, 1b
	 ADD	dst, dst, 1
l_exc:
	LOAD	t0, TI_TASK($28)
	 nop
	LOAD	t0, THREAD_BUADDR(t0)	# t0 is just past last good address
	 nop
	SUB	len, AT, t0		# len number of uncopied bytes
	/*
	 * Here's where we rely on src and dst being incremented in tandem,
	 *   See (3) above.
	 * dst += (fault addr - src) to put dst at first byte to clear
	 */
	ADD	dst, t0			# compute start address in a1
	SUB	dst, src
	/*
	 * Clear len bytes starting at dst.  Can't call __bzero because it
	 * might modify len.  An inefficient loop for these rare times...
	 */
	beqz	len, done
	 SUB	src, len, 1
1:	sb	zero, 0(dst)
	ADD	dst, dst, 1
	bnez	src, 1b
	 SUB	src, src, 1
	li	v1, -EFAULT
	b	done
	 sw	v1, (errptr)

s_exc:
	li	v0, -1 /* invalid checksum */
	li	v1, -EFAULT
	jr	ra
	 sw	v1, (errptr)
	END(__csum_partial_copy_user)