am 9088af19: am 86c31849: Merge "Create arch specific versions of strcmp."

* commit '9088af19b45d1b7339b982c92ef9113337f5d2c6':
  Create arch specific versions of strcmp.

9 files changed, 1719 insertions, 1 deletions

diff --git a/libc/arch-arm/arm.mk b/libc/arch-arm/arm.mk
index 2def30b..d15ec9d 100644
--- a/libc/arch-arm/arm.mk
+++ b/libc/arch-arm/arm.mk
@@ -14,7 +14,6 @@ _LIBC_ARCH_COMMON_SRC_FILES := \
     arch-arm/bionic/_setjmp.S \
     arch-arm/bionic/setjmp.S \
     arch-arm/bionic/sigsetjmp.S \
-    arch-arm/bionic/strcmp.S \
     arch-arm/bionic/strcpy.S \
     arch-arm/bionic/strlen.c.arm \
     arch-arm/bionic/syscall.S \
diff --git a/libc/arch-arm/cortex-a15/bionic/strcmp.S b/libc/arch-arm/cortex-a15/bionic/strcmp.S
new file mode 100644
index 0000000..7aff7c4
--- /dev/null
+++ b/libc/arch-arm/cortex-a15/bionic/strcmp.S
@@ -0,0 +1,377 @@
+/*
+ * Copyright (c) 2013 ARM Ltd
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the company may not be used to endorse or promote
+ *    products derived from this software without specific prior written
+ *    permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY ARM LTD ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL ARM LTD BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
+ * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <machine/cpu-features.h>
+#include <machine/asm.h>
+
+#ifdef __ARMEB__
+#define S2LOMEM lsl
+#define S2LOMEMEQ lsleq
+#define S2HIMEM lsr
+#define MSB 0x000000ff
+#define LSB 0xff000000
+#define BYTE0_OFFSET 24
+#define BYTE1_OFFSET 16
+#define BYTE2_OFFSET 8
+#define BYTE3_OFFSET 0
+#else /* not  __ARMEB__ */
+#define S2LOMEM lsr
+#define S2LOMEMEQ lsreq
+#define S2HIMEM lsl
+#define BYTE0_OFFSET 0
+#define BYTE1_OFFSET 8
+#define BYTE2_OFFSET 16
+#define BYTE3_OFFSET 24
+#define MSB 0xff000000
+#define LSB 0x000000ff
+#endif /* not  __ARMEB__ */
+
+.syntax         unified
+
+#if defined (__thumb__)
+        .thumb
+        .thumb_func
+#endif
+
+ENTRY(strcmp)
+      /* Use LDRD whenever possible.  */
+
+/* The main thing to look out for when comparing large blocks is that
+   the loads do not cross a page boundary when loading past the index
+   of the byte with the first difference or the first string-terminator.
+
+   For example, if the strings are identical and the string-terminator
+   is at index k, byte by byte comparison will not load beyond address
+   s1+k and s2+k; word by word comparison may load up to 3 bytes beyond
+   k; double word - up to 7 bytes.  If the load of these bytes crosses
+   a page boundary, it might cause a memory fault (if the page is not mapped)
+   that would not have happened in byte by byte comparison.
+
+   If an address is (double) word aligned, then a load of a (double) word
+   from that address will not cross a page boundary.
+   Therefore, the algorithm below considers word and double-word alignment
+   of strings separately.  */
+
+/* High-level description of the algorithm.
+
+   * The fast path: if both strings are double-word aligned,
+     use LDRD to load two words from each string in every loop iteration.
+   * If the strings have the same offset from a word boundary,
+     use LDRB to load and compare byte by byte until
+     the first string is aligned to a word boundary (at most 3 bytes).
+     This is optimized for quick return on short unaligned strings.
+   * If the strings have the same offset from a double-word boundary,
+     use LDRD to load two words from each string in every loop iteration, as in the fast path.
+   * If the strings do not have the same offset from a double-word boundary,
+     load a word from the second string before the loop to initialize the queue.
+     Use LDRD to load two words from every string in every loop iteration.
+     Inside the loop, load the second word from the second string only after comparing
+     the first word, using the queued value, to guarantee safety across page boundaries.
+   * If the strings do not have the same offset from a word boundary,
+     use LDR and a shift queue. Order of loads and comparisons matters,
+     similarly to the previous case.
+
+   * Use UADD8 and SEL to compare words, and use REV and CLZ to compute the return value.
+   * The only difference between ARM and Thumb modes is the use of CBZ instruction.
+   * The only difference between big and little endian is the use of REV in little endian
+     to compute the return value, instead of MOV.
+*/
+
+        .macro m_cbz reg label
+#ifdef __thumb2__
+        cbz     \reg, \label
+#else   /* not defined __thumb2__ */
+        cmp     \reg, #0
+        beq     \label
+#endif /* not defined __thumb2__ */
+        .endm /* m_cbz */
+
+        .macro m_cbnz reg label
+#ifdef __thumb2__
+        cbnz    \reg, \label
+#else   /* not defined __thumb2__ */
+        cmp     \reg, #0
+        bne     \label
+#endif /* not defined __thumb2__ */
+        .endm /* m_cbnz */
+
+        .macro  init
+        /* Macro to save temporary registers and prepare magic values.  */
+        subs    sp, sp, #16
+        strd    r4, r5, [sp, #8]
+        strd    r6, r7, [sp]
+        mvn     r6, #0  /* all F */
+        mov     r7, #0  /* all 0 */
+        .endm   /* init */
+
+        .macro  magic_compare_and_branch w1 w2 label
+        /* Macro to compare registers w1 and w2 and conditionally branch to label.  */
+        cmp     \w1, \w2        /* Are w1 and w2 the same?  */
+        magic_find_zero_bytes \w1
+        it      eq
+        cmpeq   ip, #0          /* Is there a zero byte in w1?  */
+        bne     \label
+        .endm /* magic_compare_and_branch */
+
+        .macro  magic_find_zero_bytes w1
+        /* Macro to find all-zero bytes in w1, result is in ip.  */
+#if (defined (__ARM_FEATURE_DSP))
+        uadd8   ip, \w1, r6
+        sel     ip, r7, r6
+#else /* not defined (__ARM_FEATURE_DSP) */
+        /* __ARM_FEATURE_DSP is not defined for some Cortex-M processors.
+        Coincidently, these processors only have Thumb-2 mode, where we can use the
+        the (large) magic constant available directly as an immediate in instructions.
+        Note that we cannot use the magic constant in ARM mode, where we need
+        to create the constant in a register.  */
+        sub     ip, \w1, #0x01010101
+        bic     ip, ip, \w1
+        and     ip, ip, #0x80808080
+#endif /* not defined (__ARM_FEATURE_DSP) */
+        .endm /* magic_find_zero_bytes */
+
+        .macro  setup_return w1 w2
+#ifdef __ARMEB__
+        mov     r1, \w1
+        mov     r2, \w2
+#else /* not  __ARMEB__ */
+        rev     r1, \w1
+        rev     r2, \w2
+#endif /* not  __ARMEB__ */
+        .endm /* setup_return */
+
+        pld [r0, #0]
+        pld [r1, #0]
+
+        /* Are both strings double-word aligned?  */
+        orr     ip, r0, r1
+        tst     ip, #7
+        bne     do_align
+
+        /* Fast path.  */
+        init
+
+doubleword_aligned:
+
+        /* Get here when the strings to compare are double-word aligned.  */
+        /* Compare two words in every iteration.  */
+        .p2align        2
+2:
+        pld [r0, #16]
+        pld [r1, #16]
+
+        /* Load the next double-word from each string.  */
+        ldrd    r2, r3, [r0], #8
+        ldrd    r4, r5, [r1], #8
+
+        magic_compare_and_branch w1=r2, w2=r4, label=return_24
+        magic_compare_and_branch w1=r3, w2=r5, label=return_35
+        b       2b
+
+do_align:
+        /* Is the first string word-aligned?  */
+        ands    ip, r0, #3
+        beq     word_aligned_r0
+
+        /* Fast compare byte by byte until the first string is word-aligned.  */
+        /* The offset of r0 from a word boundary is in ip. Thus, the number of bytes
+        to read until the next word boundary is 4-ip.  */
+        bic     r0, r0, #3
+        ldr     r2, [r0], #4
+        lsls    ip, ip, #31
+        beq     byte2
+        bcs     byte3
+
+byte1:
+        ldrb    ip, [r1], #1
+        uxtb    r3, r2, ror #BYTE1_OFFSET
+        subs    ip, r3, ip
+        bne     fast_return
+        m_cbz   reg=r3, label=fast_return
+
+byte2:
+        ldrb    ip, [r1], #1
+        uxtb    r3, r2, ror #BYTE2_OFFSET
+        subs    ip, r3, ip
+        bne     fast_return
+        m_cbz   reg=r3, label=fast_return
+
+byte3:
+        ldrb    ip, [r1], #1
+        uxtb    r3, r2, ror #BYTE3_OFFSET
+        subs    ip, r3, ip
+        bne     fast_return
+        m_cbnz  reg=r3, label=word_aligned_r0
+
+fast_return:
+        mov     r0, ip
+        bx      lr
+
+word_aligned_r0:
+        init
+        /* The first string is word-aligned.  */
+        /* Is the second string word-aligned?  */
+        ands    ip, r1, #3
+        bne     strcmp_unaligned
+
+word_aligned:
+        /* The strings are word-aligned. */
+        /* Is the first string double-word aligned?  */
+        tst     r0, #4
+        beq     doubleword_aligned_r0
+
+        /* If r0 is not double-word aligned yet, align it by loading
+        and comparing the next word from each string.  */
+        ldr     r2, [r0], #4
+        ldr     r4, [r1], #4
+        magic_compare_and_branch w1=r2 w2=r4 label=return_24
+
+doubleword_aligned_r0:
+        /* Get here when r0 is double-word aligned.  */
+        /* Is r1 doubleword_aligned?  */
+        tst     r1, #4
+        beq     doubleword_aligned
+
+        /* Get here when the strings to compare are word-aligned,
+        r0 is double-word aligned, but r1 is not double-word aligned.  */
+
+        /* Initialize the queue.  */
+        ldr     r5, [r1], #4
+
+        /* Compare two words in every iteration.  */
+        .p2align        2
+3:
+        pld [r0, #16]
+        pld [r1, #16]
+
+        /* Load the next double-word from each string and compare.  */
+        ldrd    r2, r3, [r0], #8
+        magic_compare_and_branch w1=r2 w2=r5 label=return_25
+        ldrd    r4, r5, [r1], #8
+        magic_compare_and_branch w1=r3 w2=r4 label=return_34
+        b       3b
+
+        .macro miscmp_word offsetlo offsethi
+        /* Macro to compare misaligned strings.  */
+        /* r0, r1 are word-aligned, and at least one of the strings
+        is not double-word aligned.  */
+        /* Compare one word in every loop iteration.  */
+        /* OFFSETLO is the original bit-offset of r1 from a word-boundary,
+        OFFSETHI is 32 - OFFSETLO (i.e., offset from the next word).  */
+
+        /* Initialize the shift queue.  */
+        ldr     r5, [r1], #4
+
+        /* Compare one word from each string in every loop iteration.  */
+        .p2align        2
+7:
+        ldr     r3, [r0], #4
+        S2LOMEM r5, r5, #\offsetlo
+        magic_find_zero_bytes w1=r3
+        cmp     r7, ip, S2HIMEM #\offsetlo
+        and     r2, r3, r6, S2LOMEM #\offsetlo
+        it      eq
+        cmpeq   r2, r5
+        bne     return_25
+        ldr     r5, [r1], #4
+        cmp     ip, #0
+        eor r3, r2, r3
+        S2HIMEM r2, r5, #\offsethi
+        it      eq
+        cmpeq   r3, r2
+        bne     return_32
+        b       7b
+        .endm /* miscmp_word */
+
+strcmp_unaligned:
+        /* r0 is word-aligned, r1 is at offset ip from a word.  */
+        /* Align r1 to the (previous) word-boundary.  */
+        bic     r1, r1, #3
+
+        /* Unaligned comparison word by word using LDRs. */
+        cmp     ip, #2
+        beq     miscmp_word_16                    /* If ip == 2.  */
+        bge     miscmp_word_24                    /* If ip == 3.  */
+        miscmp_word offsetlo=8 offsethi=24        /* If ip == 1.  */
+miscmp_word_16:  miscmp_word offsetlo=16 offsethi=16
+miscmp_word_24:  miscmp_word offsetlo=24 offsethi=8
+
+
+return_32:
+        setup_return w1=r3, w2=r2
+        b       do_return
+return_34:
+        setup_return w1=r3, w2=r4
+        b       do_return
+return_25:
+        setup_return w1=r2, w2=r5
+        b       do_return
+return_35:
+        setup_return w1=r3, w2=r5
+        b       do_return
+return_24:
+        setup_return w1=r2, w2=r4
+
+do_return:
+
+#ifdef __ARMEB__
+        mov     r0, ip
+#else /* not  __ARMEB__ */
+        rev     r0, ip
+#endif /* not  __ARMEB__ */
+
+        /* Restore temporaries early, before computing the return value.  */
+        ldrd    r6, r7, [sp]
+        ldrd    r4, r5, [sp, #8]
+        adds    sp, sp, #16
+
+        /* There is a zero or a different byte between r1 and r2.  */
+        /* r0 contains a mask of all-zero bytes in r1.  */
+        /* Using r0 and not ip here because cbz requires low register.  */
+        m_cbz   reg=r0, label=compute_return_value
+        clz     r0, r0
+        /* r0 contains the number of bits on the left of the first all-zero byte in r1.  */
+        rsb     r0, r0, #24
+        /* Here, r0 contains the number of bits on the right of the first all-zero byte in r1.  */
+        lsr     r1, r1, r0
+        lsr     r2, r2, r0
+
+compute_return_value:
+        movs    r0, #1
+        cmp     r1, r2
+        /* The return value is computed as follows.
+        If r1>r2 then (C==1 and Z==0) and LS doesn't hold and r0 is #1 at return.
+        If r1<r2 then (C==0 and Z==0) and we execute SBC with carry_in=0,
+        which means r0:=r0-r0-1 and r0 is #-1 at return.
+        If r1=r2 then (C==1 and Z==1) and we execute SBC with carry_in=1,
+        which means r0:=r0-r0 and r0 is #0 at return.
+        (C==0 and Z==1) cannot happen because the carry bit is "not borrow".  */
+        it      ls
+        sbcls   r0, r0, r0
+        bx      lr
+END(strcmp)
diff --git a/libc/arch-arm/cortex-a15/cortex-a15.mk b/libc/arch-arm/cortex-a15/cortex-a15.mk
index 4534808..d8193f8 100644
--- a/libc/arch-arm/cortex-a15/cortex-a15.mk
+++ b/libc/arch-arm/cortex-a15/cortex-a15.mk
@@ -1,4 +1,5 @@
 $(call libc-add-cpu-variant-src,MEMCPY,arch-arm/cortex-a15/bionic/memcpy.S)
 $(call libc-add-cpu-variant-src,MEMSET,arch-arm/cortex-a15/bionic/memset.S)
+$(call libc-add-cpu-variant-src,STRCMP,arch-arm/cortex-a15/bionic/strcmp.S)
 
 include bionic/libc/arch-arm/generic/generic.mk
diff --git a/libc/arch-arm/cortex-a9/bionic/strcmp.S b/libc/arch-arm/cortex-a9/bionic/strcmp.S
new file mode 100644
index 0000000..9597d0d
--- /dev/null
+++ b/libc/arch-arm/cortex-a9/bionic/strcmp.S
@@ -0,0 +1,544 @@
+/*
+ * Copyright (c) 2013 ARM Ltd
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the company may not be used to endorse or promote
+ *    products derived from this software without specific prior written
+ *    permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY ARM LTD ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL ARM LTD BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
+ * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <machine/cpu-features.h>
+#include <machine/asm.h>
+
+#ifdef __ARMEB__
+#define S2LOMEM lsl
+#define S2LOMEMEQ lsleq
+#define S2HIMEM lsr
+#define MSB 0x000000ff
+#define LSB 0xff000000
+#define BYTE0_OFFSET 24
+#define BYTE1_OFFSET 16
+#define BYTE2_OFFSET 8
+#define BYTE3_OFFSET 0
+#else /* not  __ARMEB__ */
+#define S2LOMEM lsr
+#define S2LOMEMEQ lsreq
+#define S2HIMEM lsl
+#define BYTE0_OFFSET 0
+#define BYTE1_OFFSET 8
+#define BYTE2_OFFSET 16
+#define BYTE3_OFFSET 24
+#define MSB 0xff000000
+#define LSB 0x000000ff
+#endif /* not  __ARMEB__ */
+
+.syntax         unified
+
+#if defined (__thumb__)
+        .thumb
+        .thumb_func
+#endif
+
+ENTRY(strcmp)
+      /* Use LDRD whenever possible.  */
+
+/* The main thing to look out for when comparing large blocks is that
+   the loads do not cross a page boundary when loading past the index
+   of the byte with the first difference or the first string-terminator.
+
+   For example, if the strings are identical and the string-terminator
+   is at index k, byte by byte comparison will not load beyond address
+   s1+k and s2+k; word by word comparison may load up to 3 bytes beyond
+   k; double word - up to 7 bytes.  If the load of these bytes crosses
+   a page boundary, it might cause a memory fault (if the page is not mapped)
+   that would not have happened in byte by byte comparison.
+
+   If an address is (double) word aligned, then a load of a (double) word
+   from that address will not cross a page boundary.
+   Therefore, the algorithm below considers word and double-word alignment
+   of strings separately.  */
+
+/* High-level description of the algorithm.
+
+   * The fast path: if both strings are double-word aligned,
+     use LDRD to load two words from each string in every loop iteration.
+   * If the strings have the same offset from a word boundary,
+     use LDRB to load and compare byte by byte until
+     the first string is aligned to a word boundary (at most 3 bytes).
+     This is optimized for quick return on short unaligned strings.
+   * If the strings have the same offset from a double-word boundary,
+     use LDRD to load two words from each string in every loop iteration, as in the fast path.
+   * If the strings do not have the same offset from a double-word boundary,
+     load a word from the second string before the loop to initialize the queue.
+     Use LDRD to load two words from every string in every loop iteration.
+     Inside the loop, load the second word from the second string only after comparing
+     the first word, using the queued value, to guarantee safety across page boundaries.
+   * If the strings do not have the same offset from a word boundary,
+     use LDR and a shift queue. Order of loads and comparisons matters,
+     similarly to the previous case.
+
+   * Use UADD8 and SEL to compare words, and use REV and CLZ to compute the return value.
+   * The only difference between ARM and Thumb modes is the use of CBZ instruction.
+   * The only difference between big and little endian is the use of REV in little endian
+     to compute the return value, instead of MOV.
+*/
+
+        .macro m_cbz reg label
+#ifdef __thumb2__
+        cbz     \reg, \label
+#else   /* not defined __thumb2__ */
+        cmp     \reg, #0
+        beq     \label
+#endif /* not defined __thumb2__ */
+        .endm /* m_cbz */
+
+        .macro m_cbnz reg label
+#ifdef __thumb2__
+        cbnz    \reg, \label
+#else   /* not defined __thumb2__ */
+        cmp     \reg, #0
+        bne     \label
+#endif /* not defined __thumb2__ */
+        .endm /* m_cbnz */
+
+        .macro  init
+        /* Macro to save temporary registers and prepare magic values.  */
+        subs    sp, sp, #16
+        strd    r4, r5, [sp, #8]
+        strd    r6, r7, [sp]
+        mvn     r6, #0  /* all F */
+        mov     r7, #0  /* all 0 */
+        .endm   /* init */
+
+        .macro  magic_compare_and_branch w1 w2 label
+        /* Macro to compare registers w1 and w2 and conditionally branch to label.  */
+        cmp     \w1, \w2        /* Are w1 and w2 the same?  */
+        magic_find_zero_bytes \w1
+        it      eq
+        cmpeq   ip, #0          /* Is there a zero byte in w1?  */
+        bne     \label
+        .endm /* magic_compare_and_branch */
+
+        .macro  magic_find_zero_bytes w1
+        /* Macro to find all-zero bytes in w1, result is in ip.  */
+#if (defined (__ARM_FEATURE_DSP))
+        uadd8   ip, \w1, r6
+        sel     ip, r7, r6
+#else /* not defined (__ARM_FEATURE_DSP) */
+        /* __ARM_FEATURE_DSP is not defined for some Cortex-M processors.
+        Coincidently, these processors only have Thumb-2 mode, where we can use the
+        the (large) magic constant available directly as an immediate in instructions.
+        Note that we cannot use the magic constant in ARM mode, where we need
+        to create the constant in a register.  */
+        sub     ip, \w1, #0x01010101
+        bic     ip, ip, \w1
+        and     ip, ip, #0x80808080
+#endif /* not defined (__ARM_FEATURE_DSP) */
+        .endm /* magic_find_zero_bytes */
+
+        .macro  setup_return w1 w2
+#ifdef __ARMEB__
+        mov     r1, \w1
+        mov     r2, \w2
+#else /* not  __ARMEB__ */
+        rev     r1, \w1
+        rev     r2, \w2
+#endif /* not  __ARMEB__ */
+        .endm /* setup_return */
+
+        pld [r0, #0]
+        pld [r1, #0]
+
+        /* Are both strings double-word aligned?  */
+        orr     ip, r0, r1
+        tst     ip, #7
+        bne     do_align
+
+        /* Fast path.  */
+        init
+
+doubleword_aligned:
+
+        /* Get here when the strings to compare are double-word aligned.  */
+        /* Compare two words in every iteration.  */
+        .p2align        2
+2:
+        pld [r0, #16]
+        pld [r1, #16]
+
+        /* Load the next double-word from each string.  */
+        ldrd    r2, r3, [r0], #8
+        ldrd    r4, r5, [r1], #8
+
+        magic_compare_and_branch w1=r2, w2=r4, label=return_24
+        magic_compare_and_branch w1=r3, w2=r5, label=return_35
+        b       2b
+
+do_align:
+        /* Is the first string word-aligned?  */
+        ands    ip, r0, #3
+        beq     word_aligned_r0
+
+        /* Fast compare byte by byte until the first string is word-aligned.  */
+        /* The offset of r0 from a word boundary is in ip. Thus, the number of bytes
+        to read until the next word boundary is 4-ip.  */
+        bic     r0, r0, #3
+        ldr     r2, [r0], #4
+        lsls    ip, ip, #31
+        beq     byte2
+        bcs     byte3
+
+byte1:
+        ldrb    ip, [r1], #1
+        uxtb    r3, r2, ror #BYTE1_OFFSET
+        subs    ip, r3, ip
+        bne     fast_return
+        m_cbz   reg=r3, label=fast_return
+
+byte2:
+        ldrb    ip, [r1], #1
+        uxtb    r3, r2, ror #BYTE2_OFFSET
+        subs    ip, r3, ip
+        bne     fast_return
+        m_cbz   reg=r3, label=fast_return
+
+byte3:
+        ldrb    ip, [r1], #1
+        uxtb    r3, r2, ror #BYTE3_OFFSET
+        subs    ip, r3, ip
+        bne     fast_return
+        m_cbnz  reg=r3, label=word_aligned_r0
+
+fast_return:
+        mov     r0, ip
+        bx      lr
+
+word_aligned_r0:
+        init
+        /* The first string is word-aligned.  */
+        /* Is the second string word-aligned?  */
+        ands    ip, r1, #3
+        bne     strcmp_unaligned
+
+word_aligned:
+        /* The strings are word-aligned. */
+        /* Is the first string double-word aligned?  */
+        tst     r0, #4
+        beq     doubleword_aligned_r0
+
+        /* If r0 is not double-word aligned yet, align it by loading
+        and comparing the next word from each string.  */
+        ldr     r2, [r0], #4
+        ldr     r4, [r1], #4
+        magic_compare_and_branch w1=r2 w2=r4 label=return_24
+
+doubleword_aligned_r0:
+        /* Get here when r0 is double-word aligned.  */
+        /* Is r1 doubleword_aligned?  */
+        tst     r1, #4
+        beq     doubleword_aligned
+
+        /* Get here when the strings to compare are word-aligned,
+        r0 is double-word aligned, but r1 is not double-word aligned.  */
+
+        /* Initialize the queue.  */
+        ldr     r5, [r1], #4
+
+        /* Compare two words in every iteration.  */
+        .p2align        2
+3:
+        pld [r0, #16]
+        pld [r1, #16]
+
+        /* Load the next double-word from each string and compare.  */
+        ldrd    r2, r3, [r0], #8
+        magic_compare_and_branch w1=r2 w2=r5 label=return_25
+        ldrd    r4, r5, [r1], #8
+        magic_compare_and_branch w1=r3 w2=r4 label=return_34
+        b       3b
+
+        .macro miscmp_word offsetlo offsethi
+        /* Macro to compare misaligned strings.  */
+        /* r0, r1 are word-aligned, and at least one of the strings
+        is not double-word aligned.  */
+        /* Compare one word in every loop iteration.  */
+        /* OFFSETLO is the original bit-offset of r1 from a word-boundary,
+        OFFSETHI is 32 - OFFSETLO (i.e., offset from the next word).  */
+
+        /* Initialize the shift queue.  */
+        ldr     r5, [r1], #4
+
+        /* Compare one word from each string in every loop iteration.  */
+        .p2align        2
+7:
+        ldr     r3, [r0], #4
+        S2LOMEM r5, r5, #\offsetlo
+        magic_find_zero_bytes w1=r3
+        cmp     r7, ip, S2HIMEM #\offsetlo
+        and     r2, r3, r6, S2LOMEM #\offsetlo
+        it      eq
+        cmpeq   r2, r5
+        bne     return_25
+        ldr     r5, [r1], #4
+        cmp     ip, #0
+        eor r3, r2, r3
+        S2HIMEM r2, r5, #\offsethi
+        it      eq
+        cmpeq   r3, r2
+        bne     return_32
+        b       7b
+        .endm /* miscmp_word */
+
+return_32:
+        setup_return w1=r3, w2=r2
+        b       do_return
+return_34:
+        setup_return w1=r3, w2=r4
+        b       do_return
+return_25:
+        setup_return w1=r2, w2=r5
+        b       do_return
+return_35:
+        setup_return w1=r3, w2=r5
+        b       do_return
+return_24:
+        setup_return w1=r2, w2=r4
+
+do_return:
+
+#ifdef __ARMEB__
+        mov     r0, ip
+#else /* not  __ARMEB__ */
+        rev     r0, ip
+#endif /* not  __ARMEB__ */
+
+        /* Restore temporaries early, before computing the return value.  */
+        ldrd    r6, r7, [sp]
+        ldrd    r4, r5, [sp, #8]
+        adds    sp, sp, #16
+
+        /* There is a zero or a different byte between r1 and r2.  */
+        /* r0 contains a mask of all-zero bytes in r1.  */
+        /* Using r0 and not ip here because cbz requires low register.  */
+        m_cbz   reg=r0, label=compute_return_value
+        clz     r0, r0
+        /* r0 contains the number of bits on the left of the first all-zero byte in r1.  */
+        rsb     r0, r0, #24
+        /* Here, r0 contains the number of bits on the right of the first all-zero byte in r1.  */
+        lsr     r1, r1, r0
+        lsr     r2, r2, r0
+
+compute_return_value:
+        movs    r0, #1
+        cmp     r1, r2
+        /* The return value is computed as follows.
+        If r1>r2 then (C==1 and Z==0) and LS doesn't hold and r0 is #1 at return.
+        If r1<r2 then (C==0 and Z==0) and we execute SBC with carry_in=0,
+        which means r0:=r0-r0-1 and r0 is #-1 at return.
+        If r1=r2 then (C==1 and Z==1) and we execute SBC with carry_in=1,
+        which means r0:=r0-r0 and r0 is #0 at return.
+        (C==0 and Z==1) cannot happen because the carry bit is "not borrow".  */
+        it      ls
+        sbcls   r0, r0, r0
+        bx      lr
+
+    /* The code from the previous version of strcmp.S handles all of the
+     * cases where the first string and seconds string cannot both be
+     * aligned to a word boundary faster than the new algorithm. See
+     * bionic/libc/arch-arm/cortex-a15/bionic/strcmp.S for the unedited
+     * version of the code.
+     */
+strcmp_unaligned:
+	wp1 .req r0
+	wp2 .req r1
+	b1  .req r2
+	w1  .req r4
+	w2  .req r5
+	t1  .req ip
+	@ r3 is scratch
+
+2:
+	mov	b1, #1
+	orr	b1, b1, b1, lsl #8
+	orr	b1, b1, b1, lsl #16
+
+	and	t1, wp2, #3
+	bic	wp2, wp2, #3
+	ldr	w1, [wp1], #4
+	ldr	w2, [wp2], #4
+	cmp	t1, #2
+	beq	2f
+	bhi	3f
+
+	/* Critical inner Loop: Block with 3 bytes initial overlap */
+	.p2align	2
+1:
+	bic	t1, w1, #MSB
+	cmp	t1, w2, S2LOMEM #8
+	sub	r3, w1, b1
+	bic	r3, r3, w1
+	bne	4f
+	ands	r3, r3, b1, lsl #7
+	it	eq
+	ldreq	w2, [wp2], #4
+	bne	5f
+	eor	t1, t1, w1
+	cmp	t1, w2, S2HIMEM #24
+	bne	6f
+	ldr	w1, [wp1], #4
+	b	1b
+4:
+	S2LOMEM	w2, w2, #8
+	b	8f
+
+5:
+#ifdef __ARMEB__
+	/* The syndrome value may contain false ones if the string ends
+	 * with the bytes 0x01 0x00
+	 */
+	tst	w1, #0xff000000
+	itt	ne
+	tstne	w1, #0x00ff0000
+	tstne	w1, #0x0000ff00
+	beq	7f
+#else
+	bics	r3, r3, #0xff000000
+	bne	7f
+#endif
+	ldrb	w2, [wp2]
+	S2LOMEM	t1, w1, #24
+#ifdef __ARMEB__
+	lsl	w2, w2, #24
+#endif
+	b	8f
+
+6:
+	S2LOMEM	t1, w1, #24
+	and	w2, w2, #LSB
+	b	8f
+
+	/* Critical inner Loop: Block with 2 bytes initial overlap */
+	.p2align	2
+2:
+	S2HIMEM	t1, w1, #16
+	sub	r3, w1, b1
+	S2LOMEM	t1, t1, #16
+	bic	r3, r3, w1
+	cmp	t1, w2, S2LOMEM #16
+	bne	4f
+	ands	r3, r3, b1, lsl #7
+	it	eq
+	ldreq	w2, [wp2], #4
+	bne	5f
+	eor	t1, t1, w1
+	cmp	t1, w2, S2HIMEM #16
+	bne	6f
+	ldr	w1, [wp1], #4
+	b	2b
+
+5:
+#ifdef __ARMEB__
+	/* The syndrome value may contain false ones if the string ends
+	 * with the bytes 0x01 0x00
+	 */
+	tst	w1, #0xff000000
+	it	ne
+	tstne	w1, #0x00ff0000
+	beq	7f
+#else
+	lsls	r3, r3, #16
+	bne	7f
+#endif
+	ldrh	w2, [wp2]
+	S2LOMEM	t1, w1, #16
+#ifdef __ARMEB__
+	lsl	w2, w2, #16
+#endif
+	b	8f
+
+6:
+	S2HIMEM	w2, w2, #16
+	S2LOMEM	t1, w1, #16
+4:
+	S2LOMEM	w2, w2, #16
+	b	8f
+
+	/* Critical inner Loop: Block with 1 byte initial overlap */
+	.p2align	2
+3:
+	and	t1, w1, #LSB
+	cmp	t1, w2, S2LOMEM #24
+	sub	r3, w1, b1
+	bic	r3, r3, w1
+	bne	4f
+	ands	r3, r3, b1, lsl #7
+	it	eq
+	ldreq	w2, [wp2], #4
+	bne	5f
+	eor	t1, t1, w1
+	cmp	t1, w2, S2HIMEM #8
+	bne	6f
+	ldr	w1, [wp1], #4
+	b	3b
+4:
+	S2LOMEM	w2, w2, #24
+	b	8f
+5:
+	/* The syndrome value may contain false ones if the string ends
+	 * with the bytes 0x01 0x00
+	 */
+	tst	w1, #LSB
+	beq	7f
+	ldr	w2, [wp2], #4
+6:
+	S2LOMEM	t1, w1, #8
+	bic	w2, w2, #MSB
+	b	8f
+7:
+	mov	r0, #0
+
+    /* Restore registers and stack. */
+    ldrd    r6, r7, [sp]
+    ldrd    r4, r5, [sp, #8]
+    adds    sp, sp, #16
+
+	bx	lr
+
+8:
+	and	r2, t1, #LSB
+	and	r0, w2, #LSB
+	cmp	r0, #1
+	it	cs
+	cmpcs	r0, r2
+	itt	eq
+	S2LOMEMEQ	t1, t1, #8
+	S2LOMEMEQ	w2, w2, #8
+	beq	8b
+	sub	r0, r2, r0
+
+    /* Restore registers and stack. */
+    ldrd    r6, r7, [sp]
+    ldrd    r4, r5, [sp, #8]
+    adds    sp, sp, #16
+
+	bx	lr
+END(strcmp)
diff --git a/libc/arch-arm/cortex-a9/cortex-a9.mk b/libc/arch-arm/cortex-a9/cortex-a9.mk
index 9166413..4862933 100644
--- a/libc/arch-arm/cortex-a9/cortex-a9.mk
+++ b/libc/arch-arm/cortex-a9/cortex-a9.mk
@@ -1,4 +1,5 @@
 $(call libc-add-cpu-variant-src,MEMCPY,arch-arm/cortex-a9/bionic/memcpy.S)
 $(call libc-add-cpu-variant-src,MEMSET,arch-arm/cortex-a9/bionic/memset.S)
+$(call libc-add-cpu-variant-src,STRCMP,arch-arm/cortex-a9/bionic/strcmp.S)
 
 include bionic/libc/arch-arm/generic/generic.mk
diff --git a/libc/arch-arm/generic/bionic/strcmp.S b/libc/arch-arm/generic/bionic/strcmp.S
new file mode 100644
index 0000000..764a531
--- /dev/null
+++ b/libc/arch-arm/generic/bionic/strcmp.S
@@ -0,0 +1,317 @@
+/*
+ * Copyright (c) 2011 The Android Open Source Project
+ * Copyright (c) 2008 ARM Ltd
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the company may not be used to endorse or promote
+ *    products derived from this software without specific prior written
+ *    permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY ARM LTD ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL ARM LTD BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
+ * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <machine/cpu-features.h>
+#include <machine/asm.h>
+
+	.text
+
+#ifdef __ARMEB__
+#define SHFT2LSB lsl
+#define SHFT2LSBEQ lsleq
+#define SHFT2MSB lsr
+#define SHFT2MSBEQ lsreq
+#define MSB 0x000000ff
+#define LSB 0xff000000
+#else
+#define SHFT2LSB lsr
+#define SHFT2LSBEQ lsreq
+#define SHFT2MSB lsl
+#define SHFT2MSBEQ lsleq
+#define MSB 0xff000000
+#define LSB 0x000000ff
+#endif
+
+#define magic1(REG) REG
+#define magic2(REG) REG, lsl #7
+
+ENTRY(strcmp)
+	PLD(r0, #0)
+	PLD(r1, #0)
+	eor	r2, r0, r1
+	tst	r2, #3
+
+	/* Strings not at same byte offset from a word boundary.  */
+	bne	.Lstrcmp_unaligned
+	ands	r2, r0, #3
+	bic	r0, r0, #3
+	bic	r1, r1, #3
+	ldr	ip, [r0], #4
+	it	eq
+	ldreq	r3, [r1], #4
+	beq	1f
+
+	/* Although s1 and s2 have identical initial alignment, they are
+	 * not currently word aligned.  Rather than comparing bytes,
+	 * make sure that any bytes fetched from before the addressed
+	 * bytes are forced to 0xff.  Then they will always compare
+	 * equal.
+	 */
+	eor	r2, r2, #3
+	lsl	r2, r2, #3
+	mvn	r3, #MSB
+	SHFT2LSB	r2, r3, r2
+	ldr	r3, [r1], #4
+	orr	ip, ip, r2
+	orr	r3, r3, r2
+1:
+	/* Load the 'magic' constant 0x01010101. */
+	str	r4, [sp, #-4]!
+	mov	r4, #1
+	orr	r4, r4, r4, lsl #8
+	orr	r4, r4, r4, lsl #16
+	.p2align	2
+4:
+	PLD(r0, #8)
+	PLD(r1, #8)
+	sub	r2, ip, magic1(r4)
+	cmp	ip, r3
+	itttt	eq
+
+	/* check for any zero bytes in first word */
+	biceq	r2, r2, ip
+	tsteq	r2, magic2(r4)
+	ldreq	ip, [r0], #4
+	ldreq	r3, [r1], #4
+	beq	4b
+2:
+	/* There's a zero or a different byte in the word */
+	SHFT2MSB	r0, ip, #24
+	SHFT2LSB	ip, ip, #8
+	cmp	r0, #1
+	it	cs
+	cmpcs	r0, r3, SHFT2MSB #24
+	it	eq
+	SHFT2LSBEQ r3, r3, #8
+	beq	2b
+	/* On a big-endian machine, r0 contains the desired byte in bits
+	 * 0-7; on a little-endian machine they are in bits 24-31.  In
+	 * both cases the other bits in r0 are all zero.  For r3 the
+	 * interesting byte is at the other end of the word, but the
+	 * other bits are not necessarily zero.  We need a signed result
+	 * representing the differnece in the unsigned bytes, so for the
+	 * little-endian case we can't just shift the interesting bits up.
+	 */
+#ifdef __ARMEB__
+	sub	r0, r0, r3, lsr #24
+#else
+	and	r3, r3, #255
+	/* No RSB instruction in Thumb2 */
+#ifdef __thumb2__
+	lsr	r0, r0, #24
+	sub	r0, r0, r3
+#else
+	rsb	r0, r3, r0, lsr #24
+#endif
+#endif
+	ldr	r4, [sp], #4
+	bx	lr
+
+.Lstrcmp_unaligned:
+	wp1 .req r0
+	wp2 .req r1
+	b1  .req r2
+	w1  .req r4
+	w2  .req r5
+	t1  .req ip
+	@ r3 is scratch
+
+	/* First of all, compare bytes until wp1(sp1) is word-aligned. */
+1:
+	tst	wp1, #3
+	beq	2f
+	ldrb	r2, [wp1], #1
+	ldrb	r3, [wp2], #1
+	cmp	r2, #1
+	it	cs
+	cmpcs	r2, r3
+	beq	1b
+	sub	r0, r2, r3
+	bx	lr
+
+2:
+	str	r5, [sp, #-4]!
+	str	r4, [sp, #-4]!
+	mov	b1, #1
+	orr	b1, b1, b1, lsl #8
+	orr	b1, b1, b1, lsl #16
+
+	and	t1, wp2, #3
+	bic	wp2, wp2, #3
+	ldr	w1, [wp1], #4
+	ldr	w2, [wp2], #4
+	cmp	t1, #2
+	beq	2f
+	bhi	3f
+
+	/* Critical inner Loop: Block with 3 bytes initial overlap */
+	.p2align	2
+1:
+	bic	t1, w1, #MSB
+	cmp	t1, w2, SHFT2LSB #8
+	sub	r3, w1, b1
+	bic	r3, r3, w1
+	bne	4f
+	ands	r3, r3, b1, lsl #7
+	it	eq
+	ldreq	w2, [wp2], #4
+	bne	5f
+	eor	t1, t1, w1
+	cmp	t1, w2, SHFT2MSB #24
+	bne	6f
+	ldr	w1, [wp1], #4
+	b	1b
+4:
+	SHFT2LSB	w2, w2, #8
+	b	8f
+
+5:
+#ifdef __ARMEB__
+	/* The syndrome value may contain false ones if the string ends
+	 * with the bytes 0x01 0x00
+	 */
+	tst	w1, #0xff000000
+	itt	ne
+	tstne	w1, #0x00ff0000
+	tstne	w1, #0x0000ff00
+	beq	7f
+#else
+	bics	r3, r3, #0xff000000
+	bne	7f
+#endif
+	ldrb	w2, [wp2]
+	SHFT2LSB	t1, w1, #24
+#ifdef __ARMEB__
+	lsl	w2, w2, #24
+#endif
+	b	8f
+
+6:
+	SHFT2LSB	t1, w1, #24
+	and	w2, w2, #LSB
+	b	8f
+
+	/* Critical inner Loop: Block with 2 bytes initial overlap */
+	.p2align	2
+2:
+	SHFT2MSB	t1, w1, #16
+	sub	r3, w1, b1
+	SHFT2LSB	t1, t1, #16
+	bic	r3, r3, w1
+	cmp	t1, w2, SHFT2LSB #16
+	bne	4f
+	ands	r3, r3, b1, lsl #7
+	it	eq
+	ldreq	w2, [wp2], #4
+	bne	5f
+	eor	t1, t1, w1
+	cmp	t1, w2, SHFT2MSB #16
+	bne	6f
+	ldr	w1, [wp1], #4
+	b	2b
+
+5:
+#ifdef __ARMEB__
+	/* The syndrome value may contain false ones if the string ends
+	 * with the bytes 0x01 0x00
+	 */
+	tst	w1, #0xff000000
+	it	ne
+	tstne	w1, #0x00ff0000
+	beq	7f
+#else
+	lsls	r3, r3, #16
+	bne	7f
+#endif
+	ldrh	w2, [wp2]
+	SHFT2LSB	t1, w1, #16
+#ifdef __ARMEB__
+	lsl	w2, w2, #16
+#endif
+	b	8f
+
+6:
+	SHFT2MSB	w2, w2, #16
+	SHFT2LSB	t1, w1, #16
+4:
+	SHFT2LSB	w2, w2, #16
+	b	8f
+
+	/* Critical inner Loop: Block with 1 byte initial overlap */
+	.p2align	2
+3:
+	and	t1, w1, #LSB
+	cmp	t1, w2, SHFT2LSB #24
+	sub	r3, w1, b1
+	bic	r3, r3, w1
+	bne	4f
+	ands	r3, r3, b1, lsl #7
+	it	eq
+	ldreq	w2, [wp2], #4
+	bne	5f
+	eor	t1, t1, w1
+	cmp	t1, w2, SHFT2MSB #8
+	bne	6f
+	ldr	w1, [wp1], #4
+	b	3b
+4:
+	SHFT2LSB	w2, w2, #24
+	b	8f
+5:
+	/* The syndrome value may contain false ones if the string ends
+	 * with the bytes 0x01 0x00
+	 */
+	tst	w1, #LSB
+	beq	7f
+	ldr	w2, [wp2], #4
+6:
+	SHFT2LSB	t1, w1, #8
+	bic	w2, w2, #MSB
+	b	8f
+7:
+	mov	r0, #0
+	ldr	r4, [sp], #4
+	ldr	r5, [sp], #4
+	bx	lr
+
+8:
+	and	r2, t1, #LSB
+	and	r0, w2, #LSB
+	cmp	r0, #1
+	it	cs
+	cmpcs	r0, r2
+	itt	eq
+	SHFT2LSBEQ	t1, t1, #8
+	SHFT2LSBEQ	w2, w2, #8
+	beq	8b
+	sub	r0, r2, r0
+	ldr	r4, [sp], #4
+	ldr	r5, [sp], #4
+	bx	lr
+END(strcmp)
diff --git a/libc/arch-arm/generic/generic.mk b/libc/arch-arm/generic/generic.mk
index 46bd067..358b1e6 100644
--- a/libc/arch-arm/generic/generic.mk
+++ b/libc/arch-arm/generic/generic.mk
@@ -1,2 +1,3 @@
 $(call libc-add-cpu-variant-src,MEMCPY,arch-arm/generic/bionic/memcpy.S)
 $(call libc-add-cpu-variant-src,MEMSET,arch-arm/generic/bionic/memset.S)
+$(call libc-add-cpu-variant-src,STRCMP,arch-arm/generic/bionic/strcmp.S)
diff --git a/libc/arch-arm/krait/bionic/strcmp.S b/libc/arch-arm/krait/bionic/strcmp.S
new file mode 100644
index 0000000..d614b9d
--- /dev/null
+++ b/libc/arch-arm/krait/bionic/strcmp.S
@@ -0,0 +1,477 @@
+/*
+ * Copyright (c) 2013 ARM Ltd
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the company may not be used to endorse or promote
+ *    products derived from this software without specific prior written
+ *    permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY ARM LTD ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL ARM LTD BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
+ * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <machine/cpu-features.h>
+#include <machine/asm.h>
+
+#ifdef __ARMEB__
+#define S2LOMEM lsl
+#define S2LOMEMEQ lsleq
+#define S2HIMEM lsr
+#define MSB 0x000000ff
+#define LSB 0xff000000
+#define BYTE0_OFFSET 24
+#define BYTE1_OFFSET 16
+#define BYTE2_OFFSET 8
+#define BYTE3_OFFSET 0
+#else /* not  __ARMEB__ */
+#define S2LOMEM lsr
+#define S2LOMEMEQ lsreq
+#define S2HIMEM lsl
+#define BYTE0_OFFSET 0
+#define BYTE1_OFFSET 8
+#define BYTE2_OFFSET 16
+#define BYTE3_OFFSET 24
+#define MSB 0xff000000
+#define LSB 0x000000ff
+#endif /* not  __ARMEB__ */
+
+.syntax         unified
+
+#if defined (__thumb__)
+        .thumb
+        .thumb_func
+#endif
+
+ENTRY(strcmp)
+      /* Use LDRD whenever possible.  */
+
+/* The main thing to look out for when comparing large blocks is that
+   the loads do not cross a page boundary when loading past the index
+   of the byte with the first difference or the first string-terminator.
+
+   For example, if the strings are identical and the string-terminator
+   is at index k, byte by byte comparison will not load beyond address
+   s1+k and s2+k; word by word comparison may load up to 3 bytes beyond
+   k; double word - up to 7 bytes.  If the load of these bytes crosses
+   a page boundary, it might cause a memory fault (if the page is not mapped)
+   that would not have happened in byte by byte comparison.
+
+   If an address is (double) word aligned, then a load of a (double) word
+   from that address will not cross a page boundary.
+   Therefore, the algorithm below considers word and double-word alignment
+   of strings separately.  */
+
+/* High-level description of the algorithm.
+
+   * The fast path: if both strings are double-word aligned,
+     use LDRD to load two words from each string in every loop iteration.
+   * If the strings have the same offset from a word boundary,
+     use LDRB to load and compare byte by byte until
+     the first string is aligned to a word boundary (at most 3 bytes).
+     This is optimized for quick return on short unaligned strings.
+   * If the strings have the same offset from a double-word boundary,
+     use LDRD to load two words from each string in every loop iteration, as in the fast path.
+   * If the strings do not have the same offset from a double-word boundary,
+     load a word from the second string before the loop to initialize the queue.
+     Use LDRD to load two words from every string in every loop iteration.
+     Inside the loop, load the second word from the second string only after comparing
+     the first word, using the queued value, to guarantee safety across page boundaries.
+   * If the strings do not have the same offset from a word boundary,
+     use LDR and a shift queue. Order of loads and comparisons matters,
+     similarly to the previous case.
+
+   * Use UADD8 and SEL to compare words, and use REV and CLZ to compute the return value.
+   * The only difference between ARM and Thumb modes is the use of CBZ instruction.
+   * The only difference between big and little endian is the use of REV in little endian
+     to compute the return value, instead of MOV.
+*/
+
+        .macro m_cbz reg label
+#ifdef __thumb2__
+        cbz     \reg, \label
+#else   /* not defined __thumb2__ */
+        cmp     \reg, #0
+        beq     \label
+#endif /* not defined __thumb2__ */
+        .endm /* m_cbz */
+
+        .macro m_cbnz reg label
+#ifdef __thumb2__
+        cbnz    \reg, \label
+#else   /* not defined __thumb2__ */
+        cmp     \reg, #0
+        bne     \label
+#endif /* not defined __thumb2__ */
+        .endm /* m_cbnz */
+
+        .macro  init
+        /* Macro to save temporary registers and prepare magic values.  */
+        subs    sp, sp, #16
+        strd    r4, r5, [sp, #8]
+        strd    r6, r7, [sp]
+        mvn     r6, #0  /* all F */
+        mov     r7, #0  /* all 0 */
+        .endm   /* init */
+
+        .macro  magic_compare_and_branch w1 w2 label
+        /* Macro to compare registers w1 and w2 and conditionally branch to label.  */
+        cmp     \w1, \w2        /* Are w1 and w2 the same?  */
+        magic_find_zero_bytes \w1
+        it      eq
+        cmpeq   ip, #0          /* Is there a zero byte in w1?  */
+        bne     \label
+        .endm /* magic_compare_and_branch */
+
+        .macro  magic_find_zero_bytes w1
+        /* Macro to find all-zero bytes in w1, result is in ip.  */
+#if (defined (__ARM_FEATURE_DSP))
+        uadd8   ip, \w1, r6
+        sel     ip, r7, r6
+#else /* not defined (__ARM_FEATURE_DSP) */
+        /* __ARM_FEATURE_DSP is not defined for some Cortex-M processors.
+        Coincidently, these processors only have Thumb-2 mode, where we can use the
+        the (large) magic constant available directly as an immediate in instructions.
+        Note that we cannot use the magic constant in ARM mode, where we need
+        to create the constant in a register.  */
+        sub     ip, \w1, #0x01010101
+        bic     ip, ip, \w1
+        and     ip, ip, #0x80808080
+#endif /* not defined (__ARM_FEATURE_DSP) */
+        .endm /* magic_find_zero_bytes */
+
+        .macro  setup_return w1 w2
+#ifdef __ARMEB__
+        mov     r1, \w1
+        mov     r2, \w2
+#else /* not  __ARMEB__ */
+        rev     r1, \w1
+        rev     r2, \w2
+#endif /* not  __ARMEB__ */
+        .endm /* setup_return */
+
+        pld [r0, #0]
+        pld [r1, #0]
+
+        /* Are both strings double-word aligned?  */
+        orr     ip, r0, r1
+        tst     ip, #7
+        bne     do_align
+
+        /* Fast path.  */
+        init
+
+doubleword_aligned:
+
+        /* Get here when the strings to compare are double-word aligned.  */
+        /* Compare two words in every iteration.  */
+        .p2align        2
+2:
+        pld [r0, #16]
+        pld [r1, #16]
+
+        /* Load the next double-word from each string.  */
+        ldrd    r2, r3, [r0], #8
+        ldrd    r4, r5, [r1], #8
+
+        magic_compare_and_branch w1=r2, w2=r4, label=return_24
+        magic_compare_and_branch w1=r3, w2=r5, label=return_35
+        b       2b
+
+do_align:
+        /* Is the first string word-aligned?  */
+        ands    ip, r0, #3
+        beq     word_aligned_r0
+
+        /* Fast compare byte by byte until the first string is word-aligned.  */
+        /* The offset of r0 from a word boundary is in ip. Thus, the number of bytes
+        to read until the next word boundary is 4-ip.  */
+        bic     r0, r0, #3
+        ldr     r2, [r0], #4
+        lsls    ip, ip, #31
+        beq     byte2
+        bcs     byte3
+
+byte1:
+        ldrb    ip, [r1], #1
+        uxtb    r3, r2, ror #BYTE1_OFFSET
+        subs    ip, r3, ip
+        bne     fast_return
+        m_cbz   reg=r3, label=fast_return
+
+byte2:
+        ldrb    ip, [r1], #1
+        uxtb    r3, r2, ror #BYTE2_OFFSET
+        subs    ip, r3, ip
+        bne     fast_return
+        m_cbz   reg=r3, label=fast_return
+
+byte3:
+        ldrb    ip, [r1], #1
+        uxtb    r3, r2, ror #BYTE3_OFFSET
+        subs    ip, r3, ip
+        bne     fast_return
+        m_cbnz  reg=r3, label=word_aligned_r0
+
+fast_return:
+        mov     r0, ip
+        bx      lr
+
+word_aligned_r0:
+        init
+        /* The first string is word-aligned.  */
+        /* Is the second string word-aligned?  */
+        ands    ip, r1, #3
+        bne     strcmp_unaligned
+
+word_aligned:
+        /* The strings are word-aligned. */
+        /* Is the first string double-word aligned?  */
+        tst     r0, #4
+        beq     doubleword_aligned_r0
+
+        /* If r0 is not double-word aligned yet, align it by loading
+        and comparing the next word from each string.  */
+        ldr     r2, [r0], #4
+        ldr     r4, [r1], #4
+        magic_compare_and_branch w1=r2 w2=r4 label=return_24
+
+doubleword_aligned_r0:
+        /* Get here when r0 is double-word aligned.  */
+        /* Is r1 doubleword_aligned?  */
+        tst     r1, #4
+        beq     doubleword_aligned
+
+        /* Get here when the strings to compare are word-aligned,
+        r0 is double-word aligned, but r1 is not double-word aligned.  */
+
+        /* Initialize the queue.  */
+        ldr     r5, [r1], #4
+
+        /* Compare two words in every iteration.  */
+        .p2align        2
+3:
+        pld [r0, #16]
+        pld [r1, #16]
+
+        /* Load the next double-word from each string and compare.  */
+        ldrd    r2, r3, [r0], #8
+        magic_compare_and_branch w1=r2 w2=r5 label=return_25
+        ldrd    r4, r5, [r1], #8
+        magic_compare_and_branch w1=r3 w2=r4 label=return_34
+        b       3b
+
+        .macro miscmp_word offsetlo offsethi
+        /* Macro to compare misaligned strings.  */
+        /* r0, r1 are word-aligned, and at least one of the strings
+        is not double-word aligned.  */
+        /* Compare one word in every loop iteration.  */
+        /* OFFSETLO is the original bit-offset of r1 from a word-boundary,
+        OFFSETHI is 32 - OFFSETLO (i.e., offset from the next word).  */
+
+        /* Initialize the shift queue.  */
+        ldr     r5, [r1], #4
+
+        /* Compare one word from each string in every loop iteration.  */
+        .p2align        2
+7:
+        ldr     r3, [r0], #4
+        S2LOMEM r5, r5, #\offsetlo
+        magic_find_zero_bytes w1=r3
+        cmp     r7, ip, S2HIMEM #\offsetlo
+        and     r2, r3, r6, S2LOMEM #\offsetlo
+        it      eq
+        cmpeq   r2, r5
+        bne     return_25
+        ldr     r5, [r1], #4
+        cmp     ip, #0
+        eor r3, r2, r3
+        S2HIMEM r2, r5, #\offsethi
+        it      eq
+        cmpeq   r3, r2
+        bne     return_32
+        b       7b
+        .endm /* miscmp_word */
+
+strcmp_unaligned:
+        /* r0 is word-aligned, r1 is at offset ip from a word.  */
+        /* Align r1 to the (previous) word-boundary.  */
+        bic     r1, r1, #3
+
+        /* Unaligned comparison word by word using LDRs. */
+        cmp     ip, #2
+        beq     miscmp_word_16                    /* If ip == 2.  */
+        bge     miscmp_word_24                    /* If ip == 3.  */
+        miscmp_word offsetlo=8 offsethi=24        /* If ip == 1.  */
+miscmp_word_24:  miscmp_word offsetlo=24 offsethi=8
+
+
+return_32:
+        setup_return w1=r3, w2=r2
+        b       do_return
+return_34:
+        setup_return w1=r3, w2=r4
+        b       do_return
+return_25:
+        setup_return w1=r2, w2=r5
+        b       do_return
+return_35:
+        setup_return w1=r3, w2=r5
+        b       do_return
+return_24:
+        setup_return w1=r2, w2=r4
+
+do_return:
+
+#ifdef __ARMEB__
+        mov     r0, ip
+#else /* not  __ARMEB__ */
+        rev     r0, ip
+#endif /* not  __ARMEB__ */
+
+        /* Restore temporaries early, before computing the return value.  */
+        ldrd    r6, r7, [sp]
+        ldrd    r4, r5, [sp, #8]
+        adds    sp, sp, #16
+
+        /* There is a zero or a different byte between r1 and r2.  */
+        /* r0 contains a mask of all-zero bytes in r1.  */
+        /* Using r0 and not ip here because cbz requires low register.  */
+        m_cbz   reg=r0, label=compute_return_value
+        clz     r0, r0
+        /* r0 contains the number of bits on the left of the first all-zero byte in r1.  */
+        rsb     r0, r0, #24
+        /* Here, r0 contains the number of bits on the right of the first all-zero byte in r1.  */
+        lsr     r1, r1, r0
+        lsr     r2, r2, r0
+
+compute_return_value:
+        movs    r0, #1
+        cmp     r1, r2
+        /* The return value is computed as follows.
+        If r1>r2 then (C==1 and Z==0) and LS doesn't hold and r0 is #1 at return.
+        If r1<r2 then (C==0 and Z==0) and we execute SBC with carry_in=0,
+        which means r0:=r0-r0-1 and r0 is #-1 at return.
+        If r1=r2 then (C==1 and Z==1) and we execute SBC with carry_in=1,
+        which means r0:=r0-r0 and r0 is #0 at return.
+        (C==0 and Z==1) cannot happen because the carry bit is "not borrow".  */
+        it      ls
+        sbcls   r0, r0, r0
+        bx      lr
+
+    /* The code from the previous version of strcmp.S handles this
+     * particular case (the second string is 2 bytes off a word alignment)
+     * faster than any current version. In this very specific case, use the
+     * previous version. See bionic/libc/arch-arm/cortex-a15/bionic/strcmp.S
+     * for the unedited version of this code.
+     */
+miscmp_word_16:
+	wp1 .req r0
+	wp2 .req r1
+	b1  .req r2
+	w1  .req r4
+	w2  .req r5
+	t1  .req ip
+	@ r3 is scratch
+
+    /* At this point, wp1 (r0) has already been word-aligned. */
+2:
+	mov	b1, #1
+	orr	b1, b1, b1, lsl #8
+	orr	b1, b1, b1, lsl #16
+
+	and	t1, wp2, #3
+	bic	wp2, wp2, #3
+	ldr	w1, [wp1], #4
+	ldr	w2, [wp2], #4
+
+	/* Critical inner Loop: Block with 2 bytes initial overlap */
+	.p2align	2
+2:
+	S2HIMEM	t1, w1, #16
+	sub	r3, w1, b1
+	S2LOMEM	t1, t1, #16
+	bic	r3, r3, w1
+	cmp	t1, w2, S2LOMEM #16
+	bne	4f
+	ands	r3, r3, b1, lsl #7
+	it	eq
+	ldreq	w2, [wp2], #4
+	bne	5f
+	eor	t1, t1, w1
+	cmp	t1, w2, S2HIMEM #16
+	bne	6f
+	ldr	w1, [wp1], #4
+	b	2b
+
+5:
+#ifdef __ARMEB__
+	/* The syndrome value may contain false ones if the string ends
+	 * with the bytes 0x01 0x00
+	 */
+	tst	w1, #0xff000000
+	it	ne
+	tstne	w1, #0x00ff0000
+	beq	7f
+#else
+	lsls	r3, r3, #16
+	bne	7f
+#endif
+	ldrh	w2, [wp2]
+	S2LOMEM	t1, w1, #16
+#ifdef __ARMEB__
+	lsl	w2, w2, #16
+#endif
+	b	8f
+
+6:
+	S2HIMEM	w2, w2, #16
+	S2LOMEM	t1, w1, #16
+4:
+	S2LOMEM	w2, w2, #16
+	b	8f
+
+7:
+	mov	r0, #0
+
+    /* Restore registers and stack. */
+    ldrd    r6, r7, [sp]
+    ldrd    r4, r5, [sp, #8]
+    adds    sp, sp, #16
+
+	bx	lr
+
+8:
+	and	r2, t1, #LSB
+	and	r0, w2, #LSB
+	cmp	r0, #1
+	it	cs
+	cmpcs	r0, r2
+	itt	eq
+	S2LOMEMEQ	t1, t1, #8
+	S2LOMEMEQ	w2, w2, #8
+	beq	8b
+	sub	r0, r2, r0
+
+    /* Restore registers and stack. */
+    ldrd    r6, r7, [sp]
+    ldrd    r4, r5, [sp, #8]
+    adds    sp, sp, #16
+
+	bx	lr
+END(strcmp)
diff --git a/libc/arch-arm/krait/krait.mk b/libc/arch-arm/krait/krait.mk
index ab55d24..4847f86 100644
--- a/libc/arch-arm/krait/krait.mk
+++ b/libc/arch-arm/krait/krait.mk
@@ -1,4 +1,5 @@
 $(call libc-add-cpu-variant-src,MEMCPY,arch-arm/krait/bionic/memcpy.S)
 $(call libc-add-cpu-variant-src,MEMSET,arch-arm/krait/bionic/memset.S)
+$(call libc-add-cpu-variant-src,STRCMP,arch-arm/krait/bionic/strcmp.S)
 
 include bionic/libc/arch-arm/generic/generic.mk