arm64: lib: Implement optimized string compare routines

This patch, based on Linaro's Cortex Strings library, adds
an assembly optimized strcmp() and strncmp() functions.

Signed-off-by: Zhichang Yuan <zhichang.yuan@linaro.org>
Signed-off-by: Deepak Saxena <dsaxena@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

5 files changed, 553 insertions, 1 deletions

diff --git a/arch/arm64/include/asm/string.h b/arch/arm64/include/asm/string.h
index 3a43305cda71..6133f4970027 100644
--- a/arch/arm64/include/asm/string.h
+++ b/arch/arm64/include/asm/string.h
@@ -22,6 +22,12 @@ extern char *strrchr(const char *, int c);
 #define __HAVE_ARCH_STRCHR
 extern char *strchr(const char *, int c);
 
+#define __HAVE_ARCH_STRCMP
+extern int strcmp(const char *, const char *);
+
+#define __HAVE_ARCH_STRNCMP
+extern int strncmp(const char *, const char *, __kernel_size_t);
+
 #define __HAVE_ARCH_MEMCPY
 extern void *memcpy(void *, const void *, __kernel_size_t);
 
diff --git a/arch/arm64/kernel/arm64ksyms.c b/arch/arm64/kernel/arm64ksyms.c
index 909c18e155ea..2784a79dbdd9 100644
--- a/arch/arm64/kernel/arm64ksyms.c
+++ b/arch/arm64/kernel/arm64ksyms.c
@@ -44,6 +44,8 @@ EXPORT_SYMBOL(memstart_addr);
         /* string / mem functions */
 EXPORT_SYMBOL(strchr);
 EXPORT_SYMBOL(strrchr);
+EXPORT_SYMBOL(strcmp);
+EXPORT_SYMBOL(strncmp);
 EXPORT_SYMBOL(memset);
 EXPORT_SYMBOL(memcpy);
 EXPORT_SYMBOL(memmove);
diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile
index 112c67f2b109..aaaf6180c558 100644
--- a/arch/arm64/lib/Makefile
+++ b/arch/arm64/lib/Makefile
@@ -1,4 +1,4 @@
 lib-y           := bitops.o clear_user.o delay.o copy_from_user.o       \
                    copy_to_user.o copy_in_user.o copy_page.o            \
                    clear_page.o memchr.o memcpy.o memmove.o memset.o    \
-                   memcmp.o strchr.o strrchr.o
+                   memcmp.o strcmp.o strncmp.o strchr.o strrchr.o
diff --git a/arch/arm64/lib/strcmp.S b/arch/arm64/lib/strcmp.S
new file mode 100644
index 000000000000..42f828b06c59
--- /dev/null
+++ b/arch/arm64/lib/strcmp.S
@@ -0,0 +1,234 @@
+/*
+ * Copyright (C) 2013 ARM Ltd.
+ * Copyright (C) 2013 Linaro.
+ *
+ * This code is based on glibc cortex strings work originally authored by Linaro
+ * and re-licensed under GPLv2 for the Linux kernel. The original code can
+ * be found @
+ *
+ * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
+ * files/head:/src/aarch64/
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+/*
+ * compare two strings
+ *
+ * Parameters:
+ *      x0 - const string 1 pointer
+ *    x1 - const string 2 pointer
+ * Returns:
+ * x0 - an integer less than, equal to, or greater than zero
+ * if  s1  is  found, respectively, to be less than, to match,
+ * or be greater than s2.
+ */
+
+#define REP8_01 0x0101010101010101
+#define REP8_7f 0x7f7f7f7f7f7f7f7f
+#define REP8_80 0x8080808080808080
+
+/* Parameters and result.  */
+src1            .req    x0
+src2            .req    x1
+result          .req    x0
+
+/* Internal variables.  */
+data1           .req    x2
+data1w          .req    w2
+data2           .req    x3
+data2w          .req    w3
+has_nul         .req    x4
+diff            .req    x5
+syndrome        .req    x6
+tmp1            .req    x7
+tmp2            .req    x8
+tmp3            .req    x9
+zeroones        .req    x10
+pos             .req    x11
+
+ENTRY(strcmp)
+        eor     tmp1, src1, src2
+        mov     zeroones, #REP8_01
+        tst     tmp1, #7
+        b.ne    .Lmisaligned8
+        ands    tmp1, src1, #7
+        b.ne    .Lmutual_align
+
+        /*
+        * NUL detection works on the principle that (X - 1) & (~X) & 0x80
+        * (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
+        * can be done in parallel across the entire word.
+        */
+.Lloop_aligned:
+        ldr     data1, [src1], #8
+        ldr     data2, [src2], #8
+.Lstart_realigned:
+        sub     tmp1, data1, zeroones
+        orr     tmp2, data1, #REP8_7f
+        eor     diff, data1, data2      /* Non-zero if differences found.  */
+        bic     has_nul, tmp1, tmp2     /* Non-zero if NUL terminator.  */
+        orr     syndrome, diff, has_nul
+        cbz     syndrome, .Lloop_aligned
+        b       .Lcal_cmpresult
+
+.Lmutual_align:
+        /*
+        * Sources are mutually aligned, but are not currently at an
+        * alignment boundary.  Round down the addresses and then mask off
+        * the bytes that preceed the start point.
+        */
+        bic     src1, src1, #7
+        bic     src2, src2, #7
+        lsl     tmp1, tmp1, #3          /* Bytes beyond alignment -> bits.  */
+        ldr     data1, [src1], #8
+        neg     tmp1, tmp1              /* Bits to alignment -64.  */
+        ldr     data2, [src2], #8
+        mov     tmp2, #~0
+        /* Big-endian.  Early bytes are at MSB.  */
+CPU_BE( lsl     tmp2, tmp2, tmp1 )      /* Shift (tmp1 & 63).  */
+        /* Little-endian.  Early bytes are at LSB.  */
+CPU_LE( lsr     tmp2, tmp2, tmp1 )      /* Shift (tmp1 & 63).  */
+
+        orr     data1, data1, tmp2
+        orr     data2, data2, tmp2
+        b       .Lstart_realigned
+
+.Lmisaligned8:
+        /*
+        * Get the align offset length to compare per byte first.
+        * After this process, one string's address will be aligned.
+        */
+        and     tmp1, src1, #7
+        neg     tmp1, tmp1
+        add     tmp1, tmp1, #8
+        and     tmp2, src2, #7
+        neg     tmp2, tmp2
+        add     tmp2, tmp2, #8
+        subs    tmp3, tmp1, tmp2
+        csel    pos, tmp1, tmp2, hi /*Choose the maximum. */
+.Ltinycmp:
+        ldrb    data1w, [src1], #1
+        ldrb    data2w, [src2], #1
+        subs    pos, pos, #1
+        ccmp    data1w, #1, #0, ne  /* NZCV = 0b0000.  */
+        ccmp    data1w, data2w, #0, cs  /* NZCV = 0b0000.  */
+        b.eq    .Ltinycmp
+        cbnz    pos, 1f /*find the null or unequal...*/
+        cmp     data1w, #1
+        ccmp    data1w, data2w, #0, cs
+        b.eq    .Lstart_align /*the last bytes are equal....*/
+1:
+        sub     result, data1, data2
+        ret
+
+.Lstart_align:
+        ands    xzr, src1, #7
+        b.eq    .Lrecal_offset
+        /*process more leading bytes to make str1 aligned...*/
+        add     src1, src1, tmp3
+        add     src2, src2, tmp3
+        /*load 8 bytes from aligned str1 and non-aligned str2..*/
+        ldr     data1, [src1], #8
+        ldr     data2, [src2], #8
+
+        sub     tmp1, data1, zeroones
+        orr     tmp2, data1, #REP8_7f
+        bic     has_nul, tmp1, tmp2
+        eor     diff, data1, data2 /* Non-zero if differences found.  */
+        orr     syndrome, diff, has_nul
+        cbnz    syndrome, .Lcal_cmpresult
+        /*How far is the current str2 from the alignment boundary...*/
+        and     tmp3, tmp3, #7
+.Lrecal_offset:
+        neg     pos, tmp3
+.Lloopcmp_proc:
+        /*
+        * Divide the eight bytes into two parts. First,backwards the src2
+        * to an alignment boundary,load eight bytes from the SRC2 alignment
+        * boundary,then compare with the relative bytes from SRC1.
+        * If all 8 bytes are equal,then start the second part's comparison.
+        * Otherwise finish the comparison.
+        * This special handle can garantee all the accesses are in the
+        * thread/task space in avoid to overrange access.
+        */
+        ldr     data1, [src1,pos]
+        ldr     data2, [src2,pos]
+        sub     tmp1, data1, zeroones
+        orr     tmp2, data1, #REP8_7f
+        bic     has_nul, tmp1, tmp2
+        eor     diff, data1, data2  /* Non-zero if differences found.  */
+        orr     syndrome, diff, has_nul
+        cbnz    syndrome, .Lcal_cmpresult
+
+        /*The second part process*/
+        ldr     data1, [src1], #8
+        ldr     data2, [src2], #8
+        sub     tmp1, data1, zeroones
+        orr     tmp2, data1, #REP8_7f
+        bic     has_nul, tmp1, tmp2
+        eor     diff, data1, data2  /* Non-zero if differences found.  */
+        orr     syndrome, diff, has_nul
+        cbz     syndrome, .Lloopcmp_proc
+
+.Lcal_cmpresult:
+        /*
+        * reversed the byte-order as big-endian,then CLZ can find the most
+        * significant zero bits.
+        */
+CPU_LE( rev     syndrome, syndrome )
+CPU_LE( rev     data1, data1 )
+CPU_LE( rev     data2, data2 )
+
+        /*
+        * For big-endian we cannot use the trick with the syndrome value
+        * as carry-propagation can corrupt the upper bits if the trailing
+        * bytes in the string contain 0x01.
+        * However, if there is no NUL byte in the dword, we can generate
+        * the result directly.  We ca not just subtract the bytes as the
+        * MSB might be significant.
+        */
+CPU_BE( cbnz    has_nul, 1f )
+CPU_BE( cmp     data1, data2 )
+CPU_BE( cset    result, ne )
+CPU_BE( cneg    result, result, lo )
+CPU_BE( ret )
+CPU_BE( 1: )
+        /*Re-compute the NUL-byte detection, using a byte-reversed value. */
+CPU_BE( rev     tmp3, data1 )
+CPU_BE( sub     tmp1, tmp3, zeroones )
+CPU_BE( orr     tmp2, tmp3, #REP8_7f )
+CPU_BE( bic     has_nul, tmp1, tmp2 )
+CPU_BE( rev     has_nul, has_nul )
+CPU_BE( orr     syndrome, diff, has_nul )
+
+        clz     pos, syndrome
+        /*
+        * The MS-non-zero bit of the syndrome marks either the first bit
+        * that is different, or the top bit of the first zero byte.
+        * Shifting left now will bring the critical information into the
+        * top bits.
+        */
+        lsl     data1, data1, pos
+        lsl     data2, data2, pos
+        /*
+        * But we need to zero-extend (char is unsigned) the value and then
+        * perform a signed 32-bit subtraction.
+        */
+        lsr     data1, data1, #56
+        sub     result, data1, data2, lsr #56
+        ret
+ENDPROC(strcmp)
diff --git a/arch/arm64/lib/strncmp.S b/arch/arm64/lib/strncmp.S
new file mode 100644
index 000000000000..0224cf5a5533
--- /dev/null
+++ b/arch/arm64/lib/strncmp.S
@@ -0,0 +1,310 @@
+/*
+ * Copyright (C) 2013 ARM Ltd.
+ * Copyright (C) 2013 Linaro.
+ *
+ * This code is based on glibc cortex strings work originally authored by Linaro
+ * and re-licensed under GPLv2 for the Linux kernel. The original code can
+ * be found @
+ *
+ * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
+ * files/head:/src/aarch64/
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+/*
+ * compare two strings
+ *
+ * Parameters:
+ *  x0 - const string 1 pointer
+ *  x1 - const string 2 pointer
+ *  x2 - the maximal length to be compared
+ * Returns:
+ *  x0 - an integer less than, equal to, or greater than zero if s1 is found,
+ *     respectively, to be less than, to match, or be greater than s2.
+ */
+
+#define REP8_01 0x0101010101010101
+#define REP8_7f 0x7f7f7f7f7f7f7f7f
+#define REP8_80 0x8080808080808080
+
+/* Parameters and result.  */
+src1            .req    x0
+src2            .req    x1
+limit           .req    x2
+result          .req    x0
+
+/* Internal variables.  */
+data1           .req    x3
+data1w          .req    w3
+data2           .req    x4
+data2w          .req    w4
+has_nul         .req    x5
+diff            .req    x6
+syndrome        .req    x7
+tmp1            .req    x8
+tmp2            .req    x9
+tmp3            .req    x10
+zeroones        .req    x11
+pos             .req    x12
+limit_wd        .req    x13
+mask            .req    x14
+endloop         .req    x15
+
+ENTRY(strncmp)
+        cbz     limit, .Lret0
+        eor     tmp1, src1, src2
+        mov     zeroones, #REP8_01
+        tst     tmp1, #7
+        b.ne    .Lmisaligned8
+        ands    tmp1, src1, #7
+        b.ne    .Lmutual_align
+        /* Calculate the number of full and partial words -1.  */
+        /*
+        * when limit is mulitply of 8, if not sub 1,
+        * the judgement of last dword will wrong.
+        */
+        sub     limit_wd, limit, #1 /* limit != 0, so no underflow.  */
+        lsr     limit_wd, limit_wd, #3  /* Convert to Dwords.  */
+
+        /*
+        * NUL detection works on the principle that (X - 1) & (~X) & 0x80
+        * (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
+        * can be done in parallel across the entire word.
+        */
+.Lloop_aligned:
+        ldr     data1, [src1], #8
+        ldr     data2, [src2], #8
+.Lstart_realigned:
+        subs    limit_wd, limit_wd, #1
+        sub     tmp1, data1, zeroones
+        orr     tmp2, data1, #REP8_7f
+        eor     diff, data1, data2  /* Non-zero if differences found.  */
+        csinv   endloop, diff, xzr, pl  /* Last Dword or differences.*/
+        bics    has_nul, tmp1, tmp2 /* Non-zero if NUL terminator.  */
+        ccmp    endloop, #0, #0, eq
+        b.eq    .Lloop_aligned
+
+        /*Not reached the limit, must have found the end or a diff.  */
+        tbz     limit_wd, #63, .Lnot_limit
+
+        /* Limit % 8 == 0 => all bytes significant.  */
+        ands    limit, limit, #7
+        b.eq    .Lnot_limit
+
+        lsl     limit, limit, #3    /* Bits -> bytes.  */
+        mov     mask, #~0
+CPU_BE( lsr     mask, mask, limit )
+CPU_LE( lsl     mask, mask, limit )
+        bic     data1, data1, mask
+        bic     data2, data2, mask
+
+        /* Make sure that the NUL byte is marked in the syndrome.  */
+        orr     has_nul, has_nul, mask
+
+.Lnot_limit:
+        orr     syndrome, diff, has_nul
+        b       .Lcal_cmpresult
+
+.Lmutual_align:
+        /*
+        * Sources are mutually aligned, but are not currently at an
+        * alignment boundary.  Round down the addresses and then mask off
+        * the bytes that precede the start point.
+        * We also need to adjust the limit calculations, but without
+        * overflowing if the limit is near ULONG_MAX.
+        */
+        bic     src1, src1, #7
+        bic     src2, src2, #7
+        ldr     data1, [src1], #8
+        neg     tmp3, tmp1, lsl #3  /* 64 - bits(bytes beyond align). */
+        ldr     data2, [src2], #8
+        mov     tmp2, #~0
+        sub     limit_wd, limit, #1 /* limit != 0, so no underflow.  */
+        /* Big-endian.  Early bytes are at MSB.  */
+CPU_BE( lsl     tmp2, tmp2, tmp3 )      /* Shift (tmp1 & 63).  */
+        /* Little-endian.  Early bytes are at LSB.  */
+CPU_LE( lsr     tmp2, tmp2, tmp3 )      /* Shift (tmp1 & 63).  */
+
+        and     tmp3, limit_wd, #7
+        lsr     limit_wd, limit_wd, #3
+        /* Adjust the limit. Only low 3 bits used, so overflow irrelevant.*/
+        add     limit, limit, tmp1
+        add     tmp3, tmp3, tmp1
+        orr     data1, data1, tmp2
+        orr     data2, data2, tmp2
+        add     limit_wd, limit_wd, tmp3, lsr #3
+        b       .Lstart_realigned
+
+/*when src1 offset is not equal to src2 offset...*/
+.Lmisaligned8:
+        cmp     limit, #8
+        b.lo    .Ltiny8proc /*limit < 8... */
+        /*
+        * Get the align offset length to compare per byte first.
+        * After this process, one string's address will be aligned.*/
+        and     tmp1, src1, #7
+        neg     tmp1, tmp1
+        add     tmp1, tmp1, #8
+        and     tmp2, src2, #7
+        neg     tmp2, tmp2
+        add     tmp2, tmp2, #8
+        subs    tmp3, tmp1, tmp2
+        csel    pos, tmp1, tmp2, hi /*Choose the maximum. */
+        /*
+        * Here, limit is not less than 8, so directly run .Ltinycmp
+        * without checking the limit.*/
+        sub     limit, limit, pos
+.Ltinycmp:
+        ldrb    data1w, [src1], #1
+        ldrb    data2w, [src2], #1
+        subs    pos, pos, #1
+        ccmp    data1w, #1, #0, ne  /* NZCV = 0b0000.  */
+        ccmp    data1w, data2w, #0, cs  /* NZCV = 0b0000.  */
+        b.eq    .Ltinycmp
+        cbnz    pos, 1f /*find the null or unequal...*/
+        cmp     data1w, #1
+        ccmp    data1w, data2w, #0, cs
+        b.eq    .Lstart_align /*the last bytes are equal....*/
+1:
+        sub     result, data1, data2
+        ret
+
+.Lstart_align:
+        lsr     limit_wd, limit, #3
+        cbz     limit_wd, .Lremain8
+        /*process more leading bytes to make str1 aligned...*/
+        ands    xzr, src1, #7
+        b.eq    .Lrecal_offset
+        add     src1, src1, tmp3        /*tmp3 is positive in this branch.*/
+        add     src2, src2, tmp3
+        ldr     data1, [src1], #8
+        ldr     data2, [src2], #8
+
+        sub     limit, limit, tmp3
+        lsr     limit_wd, limit, #3
+        subs    limit_wd, limit_wd, #1
+
+        sub     tmp1, data1, zeroones
+        orr     tmp2, data1, #REP8_7f
+        eor     diff, data1, data2  /* Non-zero if differences found.  */
+        csinv   endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
+        bics    has_nul, tmp1, tmp2
+        ccmp    endloop, #0, #0, eq /*has_null is ZERO: no null byte*/
+        b.ne    .Lunequal_proc
+        /*How far is the current str2 from the alignment boundary...*/
+        and     tmp3, tmp3, #7
+.Lrecal_offset:
+        neg     pos, tmp3
+.Lloopcmp_proc:
+        /*
+        * Divide the eight bytes into two parts. First,backwards the src2
+        * to an alignment boundary,load eight bytes from the SRC2 alignment
+        * boundary,then compare with the relative bytes from SRC1.
+        * If all 8 bytes are equal,then start the second part's comparison.
+        * Otherwise finish the comparison.
+        * This special handle can garantee all the accesses are in the
+        * thread/task space in avoid to overrange access.
+        */
+        ldr     data1, [src1,pos]
+        ldr     data2, [src2,pos]
+        sub     tmp1, data1, zeroones
+        orr     tmp2, data1, #REP8_7f
+        bics    has_nul, tmp1, tmp2 /* Non-zero if NUL terminator.  */
+        eor     diff, data1, data2  /* Non-zero if differences found.  */
+        csinv   endloop, diff, xzr, eq
+        cbnz    endloop, .Lunequal_proc
+
+        /*The second part process*/
+        ldr     data1, [src1], #8
+        ldr     data2, [src2], #8
+        subs    limit_wd, limit_wd, #1
+        sub     tmp1, data1, zeroones
+        orr     tmp2, data1, #REP8_7f
+        eor     diff, data1, data2  /* Non-zero if differences found.  */
+        csinv   endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
+        bics    has_nul, tmp1, tmp2
+        ccmp    endloop, #0, #0, eq /*has_null is ZERO: no null byte*/
+        b.eq    .Lloopcmp_proc
+
+.Lunequal_proc:
+        orr     syndrome, diff, has_nul
+        cbz     syndrome, .Lremain8
+.Lcal_cmpresult:
+        /*
+        * reversed the byte-order as big-endian,then CLZ can find the most
+        * significant zero bits.
+        */
+CPU_LE( rev     syndrome, syndrome )
+CPU_LE( rev     data1, data1 )
+CPU_LE( rev     data2, data2 )
+        /*
+        * For big-endian we cannot use the trick with the syndrome value
+        * as carry-propagation can corrupt the upper bits if the trailing
+        * bytes in the string contain 0x01.
+        * However, if there is no NUL byte in the dword, we can generate
+        * the result directly.  We can't just subtract the bytes as the
+        * MSB might be significant.
+        */
+CPU_BE( cbnz    has_nul, 1f )
+CPU_BE( cmp     data1, data2 )
+CPU_BE( cset    result, ne )
+CPU_BE( cneg    result, result, lo )
+CPU_BE( ret )
+CPU_BE( 1: )
+        /* Re-compute the NUL-byte detection, using a byte-reversed value.*/
+CPU_BE( rev     tmp3, data1 )
+CPU_BE( sub     tmp1, tmp3, zeroones )
+CPU_BE( orr     tmp2, tmp3, #REP8_7f )
+CPU_BE( bic     has_nul, tmp1, tmp2 )
+CPU_BE( rev     has_nul, has_nul )
+CPU_BE( orr     syndrome, diff, has_nul )
+        /*
+        * The MS-non-zero bit of the syndrome marks either the first bit
+        * that is different, or the top bit of the first zero byte.
+        * Shifting left now will bring the critical information into the
+        * top bits.
+        */
+        clz     pos, syndrome
+        lsl     data1, data1, pos
+        lsl     data2, data2, pos
+        /*
+        * But we need to zero-extend (char is unsigned) the value and then
+        * perform a signed 32-bit subtraction.
+        */
+        lsr     data1, data1, #56
+        sub     result, data1, data2, lsr #56
+        ret
+
+.Lremain8:
+        /* Limit % 8 == 0 => all bytes significant.  */
+        ands    limit, limit, #7
+        b.eq    .Lret0
+.Ltiny8proc:
+        ldrb    data1w, [src1], #1
+        ldrb    data2w, [src2], #1
+        subs    limit, limit, #1
+
+        ccmp    data1w, #1, #0, ne  /* NZCV = 0b0000.  */
+        ccmp    data1w, data2w, #0, cs  /* NZCV = 0b0000.  */
+        b.eq    .Ltiny8proc
+        sub     result, data1, data2
+        ret
+
+.Lret0:
+        mov     result, #0
+        ret
+ENDPROC(strncmp)