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memcpy

To: Ralf Baechle <ralf@linux-mips.org>, "Maciej W. Rozycki" <macro@ds2.pg.gda.pl>, linux-mips@linux-mips.org
Subject: memcpy
From: Carsten Langgaard <carstenl@mips.com>
Date: Thu, 12 Sep 2002 10:32:25 +0200
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
I have found another bug in the 64-bit memcpy function, so I figured it
was time to use the 32-bit version (as it's more or less are prepared
for 64-bit).
With a few fixes the memcpy.S file can now be shared between the 32-bit
and 64-bit kernel (the only difference is the definition of USE_DOUBLE).

I have attached the patch for arch/mips/lib/memcpy.S and the full file
for the arch/mips64/lib/memcpy.S

/Carsten


--
_    _ ____  ___   Carsten Langgaard   Mailto:carstenl@mips.com
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Index: arch/mips/lib/memcpy.S
===================================================================
RCS file: /cvs/linux/arch/mips/lib/memcpy.S,v
retrieving revision 1.6.2.3
diff -u -r1.6.2.3 memcpy.S
--- arch/mips/lib/memcpy.S      2002/06/30 23:10:57     1.6.2.3
+++ arch/mips/lib/memcpy.S      2002/09/12 08:12:21
@@ -99,6 +99,24 @@
 #define NBYTES 8
 #define LOG_NBYTES 3
 
+/* 
+ * As we are sharing code base with the mips32 tree (which use the o32 ABI
+ * register definitions). We need to redefine the register definitions from
+ * the n64 ABI register naming to the o32 ABI register naming.
+ */
+#undef t0
+#undef t1
+#undef t2
+#undef t3
+#define t0     $8
+#define t1     $9
+#define t2     $10
+#define t3     $11
+#define t4     $12
+#define t5     $13
+#define t6     $14
+#define t7     $15
+       
 #else
 
 #define LOAD   lw
@@ -385,7 +403,7 @@
         *
         * Assumes src < THREAD_BUADDR($28)
         */
-       lw      t0, THREAD_BUADDR($28)
+       LOAD    t0, THREAD_BUADDR($28)
 1:
 EXC(   lb      t1, 0(src),     l_exc)
        ADD     src, src, 1
@@ -393,16 +411,16 @@
        bne     src, t0, 1b
         ADD    dst, dst, 1
 l_exc:
-       lw      t0, THREAD_BUADDR($28)  # t0 is just past last good address
+       LOAD    t0, THREAD_BUADDR($28)  # t0 is just past last good address
         nop
-       subu    len, AT, t0             # len number of uncopied bytes
+       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
         */
-       addu    dst, t0                 # compute start address in a1
-       subu    dst, src
+       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...
@@ -440,8 +458,8 @@
 
        .align  5
 LEAF(memmove)
-       addu    t0, a0, a2
-       addu    t1, a1, a2
+       ADD     t0, a0, a2
+       ADD     t1, a1, a2
        sltu    t0, a1, t0                      # dst + len <= src -> memcpy
        sltu    t1, a0, t1                      # dst >= src + len -> memcpy
        and     t0, t1
@@ -455,16 +473,16 @@
         sltu   t0, a1, a0
        beqz    t0, r_end_bytes_up              # src >= dst
         nop
-       addu    a0, a2                          # dst = dst + len
-       addu    a1, a2                          # src = src + len
+       ADD     a0, a2                          # dst = dst + len
+       ADD     a1, a2                          # src = src + len
 
 r_end_bytes:
        lb      t0, -1(a1)
-       subu    a2, a2, 0x1
+       SUB     a2, a2, 0x1
        sb      t0, -1(a0)
-       subu    a1, a1, 0x1
+       SUB     a1, a1, 0x1
        bnez    a2, r_end_bytes
-        subu   a0, a0, 0x1
+        SUB    a0, a0, 0x1
 
 r_out:
        jr      ra
@@ -472,11 +490,11 @@
 
 r_end_bytes_up:
        lb      t0, (a1)
-       subu    a2, a2, 0x1
+       SUB     a2, a2, 0x1
        sb      t0, (a0)
-       addu    a1, a1, 0x1
+       ADD     a1, a1, 0x1
        bnez    a2, r_end_bytes_up
-        addu   a0, a0, 0x1
+        ADD    a0, a0, 0x1
 
        jr      ra
         move   a2, zero
/*
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Unified implementation of memcpy, memmove and the __copy_user backend.
 *
 * Copyright (C) 1998, 99, 2000, 01, 2002 Ralf Baechle (ralf@gnu.org)
 * Copyright (C) 1999, 2000, 01, 2002 Silicon Graphics, Inc.
 * Copyright (C) 2002 Broadcom, Inc.
 *   memcpy/copy_user author: Mark Vandevoorde
 *
 * Mnemonic names for arguments to memcpy/__copy_user
 */
#include <linux/config.h>
#include <asm/asm.h>
#include <asm/offset.h>
#include <asm/regdef.h>

#define dst a0
#define src a1
#define len a2

/*
 * Spec
 *
 * memcpy copies len bytes from src to dst and sets v0 to dst.
 * It assumes that
 *   - src and dst don't overlap
 *   - src is readable
 *   - dst is writable
 * memcpy uses the standard calling convention
 *
 * __copy_user copies up to len bytes from src to dst and sets a2 (len) to
 * the number of uncopied bytes due to an exception caused by a read or write.
 * __copy_user assumes that src and dst don't overlap, and that the call is
 * implementing one of the following:
 *   copy_to_user
 *     - src is readable  (no exceptions when reading src)
 *   copy_from_user
 *     - dst is writable  (no exceptions when writing dst)
 * __copy_user uses a non-standard calling convention; see
 * include/asm-mips/uaccess.h
 *
 * When an exception happens on a load, the handler must
 # ensure that all of the destination buffer is overwritten to prevent
 * leaking information to user mode programs.
 */

/*
 * Implementation
 */

/*
 * The exception handler for loads requires that:
 *  1- AT contain the address of the byte just past the end of the source
 *     of the copy,
 *  2- src_entry <= src < AT, and
 *  3- (dst - src) == (dst_entry - src_entry),
 * The _entry suffix denotes values when __copy_user was called.
 *
 * (1) is set up up by uaccess.h and maintained by not writing AT in copy_user
 * (2) is met by incrementing src by the number of bytes copied
 * (3) is met by not doing loads between a pair of increments of dst and src
 *
 * The exception handlers for stores adjust len (if necessary) and return.
 * These handlers do not need to overwrite any data.
 *
 * For __rmemcpy and memmove an exception is always a kernel bug, therefore
 * they're not protected.
 */

#define EXC(inst_reg,addr,handler)              \
9:      inst_reg, addr;                         \
        .section __ex_table,"a";                \
        PTR     9b, handler;                    \
        .previous

/*
 * In the mips64 (not mips32) tree, so we use doubles
 */
#define USE_DOUBLE

#if defined(USE_DOUBLE)

#define LOAD   ld
#define LOADL  ldl
#define LOADR  ldr
#define STOREL sdl
#define STORER sdr
#define STORE  sd
#define ADD    daddu
#define SUB    dsubu
#define SRL    dsrl
#define SRA    dsra
#define SLL    dsll
#define SLLV   dsllv
#define SRLV   dsrlv
#define NBYTES 8
#define LOG_NBYTES 3

/* 
 * As we are sharing code base with the mips32 tree (which use the o32 ABI
 * register definitions). We need to redefine the register definitions from
 * the n64 ABI register naming to the o32 ABI register naming.
 */
#undef t0
#undef t1
#undef t2
#undef t3
#define t0      $8
#define t1      $9
#define t2      $10
#define t3      $11
#define t4      $12
#define t5      $13
#define t6      $14
#define t7      $15
        
#else

#define LOAD   lw
#define LOADL  lwl
#define LOADR  lwr
#define STOREL swl
#define STORER swr
#define STORE  sw
#define ADD    addu
#define SUB    subu
#define SRL    srl
#define SLL    sll
#define SRA    sra
#define SLLV   sllv
#define SRLV   srlv
#define NBYTES 4
#define LOG_NBYTES 2

#endif /* USE_DOUBLE */

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

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

#define ADDRMASK (NBYTES-1)

        .text
        .set    noreorder
        .set    noat

/*
 * A combined memcpy/__copy_user
 * __copy_user sets len to 0 for success; else to an upper bound of
 * the number of uncopied bytes.
 * memcpy sets v0 to dst.
 */
        .align  5
LEAF(memcpy)                                    /* a0=dst a1=src a2=len */
        move    v0, dst                         /* return value */
__memcpy:
FEXPORT(__copy_user)
        /*
         * Note: dst & src may be unaligned, len may be 0
         * Temps
         */
#define rem t8

        /*
         * 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.
         */
        PREF(   0, 0(src) )
        PREF(   1, 0(dst) )
        sltu    t2, len, NBYTES
        and     t1, dst, ADDRMASK
        PREF(   0, 1*32(src) )
        PREF(   1, 1*32(dst) )
        bnez    t2, copy_bytes_checklen
         and    t0, src, ADDRMASK
        PREF(   0, 2*32(src) )
        PREF(   1, 2*32(dst) )
        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
         and    rem, len, (8*NBYTES-1)   # rem = len % (8*NBYTES)
        PREF(   0, 3*32(src) )
        PREF(   1, 3*32(dst) )
        .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)
        SUB     len, len, 8*NBYTES
EXC(    LOAD    t4, UNIT(4)(src),       l_exc_copy)
EXC(    LOAD    t7, UNIT(5)(src),       l_exc_copy)
EXC(    STORE   t0, UNIT(0)(dst),       s_exc_p8u)
EXC(    STORE   t1, UNIT(1)(dst),       s_exc_p7u)
EXC(    LOAD    t0, UNIT(6)(src),       l_exc_copy)
EXC(    LOAD    t1, UNIT(7)(src),       l_exc_copy)
        ADD     src, src, 8*NBYTES
        ADD     dst, dst, 8*NBYTES
EXC(    STORE   t2, UNIT(-6)(dst),      s_exc_p6u)
EXC(    STORE   t3, UNIT(-5)(dst),      s_exc_p5u)
EXC(    STORE   t4, UNIT(-4)(dst),      s_exc_p4u)
EXC(    STORE   t7, UNIT(-3)(dst),      s_exc_p3u)
EXC(    STORE   t0, UNIT(-2)(dst),      s_exc_p2u)
EXC(    STORE   t1, UNIT(-1)(dst),      s_exc_p1u)
        PREF(   0, 8*32(src) )
        PREF(   1, 8*32(dst) )
        bne     len, rem, 1b
         nop

        /*
         * len == rem == the number of bytes left to copy < 8*NBYTES
         */
cleanup_both_aligned:
        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_p4u)
EXC(    STORE   t1, UNIT(1)(dst),       s_exc_p3u)
EXC(    STORE   t2, UNIT(2)(dst),       s_exc_p2u)
EXC(    STORE   t3, UNIT(3)(dst),       s_exc_p1u)
        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_p1u)
        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)
        jr      ra
         move   len, zero
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)
        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
        PREF(   0, 3*32(src) )
        beqz    t0, cleanup_src_unaligned
         and    rem, len, (4*NBYTES-1)   # rem = len % 4*NBYTES
        PREF(   1, 3*32(dst) )
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)
        PREF(   0, 9*32(src) )          # 0 is PREF_LOAD  (not streamed)
        ADD     src, src, 4*NBYTES
#ifdef CONFIG_CPU_SB1
        nop                             # improves slotting
#endif
EXC(    STORE   t0, UNIT(0)(dst),       s_exc_p4u)
EXC(    STORE   t1, UNIT(1)(dst),       s_exc_p3u)
EXC(    STORE   t2, UNIT(2)(dst),       s_exc_p2u)
EXC(    STORE   t3, UNIT(3)(dst),       s_exc_p1u)
        PREF(   1, 9*32(dst) )          # 1 is PREF_STORE (not streamed)
        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
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_p1u)
        bne     len, rem, 1b
         ADD    dst, dst, NBYTES

copy_bytes_checklen:
        beqz    len, done
         nop
copy_bytes:
        /* 0 < len < NBYTES  */
#define COPY_BYTE(N)                    \
EXC(    lb      t0, N(src), l_exc);     \
        SUB     len, len, 1;            \
        beqz    len, done;              \
EXC(     sb     t0, N(dst), s_exc_p1)

        COPY_BYTE(0)
        COPY_BYTE(1)
#ifdef USE_DOUBLE
        COPY_BYTE(2)
        COPY_BYTE(3)
        COPY_BYTE(4)
        COPY_BYTE(5)
#endif
EXC(    lb      t0, NBYTES-2(src), l_exc)
        SUB     len, len, 1
        jr      ra
EXC(     sb     t0, NBYTES-2(dst), s_exc_p1)
done:
        jr      ra
         nop
        END(memcpy)

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, THREAD_BUADDR($28)
1:
EXC(    lb      t1, 0(src),     l_exc)
        ADD     src, src, 1
        sb      t1, 0(dst)      # can't fault -- we're copy_from_user
        bne     src, t0, 1b
         ADD    dst, dst, 1
l_exc:
        LOAD    t0, THREAD_BUADDR($28)  # 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
        jr      ra
         nop


#define SEXC(n)                         \
s_exc_p ## n ## u:                      \
        jr      ra;                     \
         ADD    len, len, n*NBYTES

SEXC(8)
SEXC(7)
SEXC(6)
SEXC(5)
SEXC(4)
SEXC(3)
SEXC(2)
SEXC(1)

s_exc_p1:
        jr      ra
         ADD    len, len, 1
s_exc:
        jr      ra
         nop

        .align  5
LEAF(memmove)
        ADD     t0, a0, a2
        ADD     t1, a1, a2
        sltu    t0, a1, t0                      # dst + len <= src -> memcpy
        sltu    t1, a0, t1                      # dst >= src + len -> memcpy
        and     t0, t1
        beqz    t0, __memcpy
         move   v0, a0                          /* return value */
        beqz    a2, r_out
        END(memmove)

        /* fall through to __rmemcpy */
LEAF(__rmemcpy)                                 /* a0=dst a1=src a2=len */
         sltu   t0, a1, a0
        beqz    t0, r_end_bytes_up              # src >= dst
         nop
        ADD     a0, a2                          # dst = dst + len
        ADD     a1, a2                          # src = src + len

r_end_bytes:
        lb      t0, -1(a1)
        SUB     a2, a2, 0x1
        sb      t0, -1(a0)
        SUB     a1, a1, 0x1
        bnez    a2, r_end_bytes
         SUB    a0, a0, 0x1

r_out:
        jr      ra
         move   a2, zero

r_end_bytes_up:
        lb      t0, (a1)
        SUB     a2, a2, 0x1
        sb      t0, (a0)
        ADD     a1, a1, 0x1
        bnez    a2, r_end_bytes_up
         ADD    a0, a0, 0x1

        jr      ra
         move   a2, zero
        END(__rmemcpy)
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