Index: lib/builtins/arm/sync-ops.h
===================================================================
--- lib/builtins/arm/sync-ops.h
+++ lib/builtins/arm/sync-ops.h
@@ -10,11 +10,28 @@
  * This file implements outline macros for the __sync_fetch_and_*
  * operations. Different instantiations will generate appropriate assembly for
  * ARM and Thumb-2 versions of the functions.
+ * These builtins are documented here:
+ * https://gcc.gnu.org/onlinedocs/gcc/_005f_005fsync-Builtins.html
  *
  *===----------------------------------------------------------------------===*/
 
 #include "../assembly.h"
 
+#if defined(__ARM_ARCH_6M__)
+#define SYNC_OP_4(op) \
+        .thumb ; \
+        .syntax unified ; \
+        DEFINE_COMPILERRT_THUMB_FUNCTION(__sync_fetch_and_ ## op) \
+        mrs r3, PRIMASK ; \
+        cpsid i ; \
+        ldr r2, [r0] ; \
+        mov r12,  r2; \
+        op(r2, r2, r1) ; \
+        str r2, [r0] ; \
+        msr PRIMASK, r3 ; \
+        mov r0, r12 ; \
+        bx lr
+#else
 #define SYNC_OP_4(op) \
         .p2align 2 ; \
         .thumb ; \
@@ -30,7 +47,29 @@
         bne LOCAL_LABEL(tryatomic_ ## op) ; \
         dmb ; \
         bx lr
+#endif
 
+#if __ARM_ARCH_PROFILE == 'M'
+#define SYNC_OP_8(op) \
+        .thumb ; \
+        .syntax unified ; \
+        DEFINE_COMPILERRT_THUMB_FUNCTION(__sync_fetch_and_ ## op) \
+        push {r4, r5, r6, lr} ; \
+        mov r4, r0 ; \
+        mrs r5, PRIMASK ; \
+        cpsid i ; \
+        ldr r0, [r4, #0] ; \
+        ldr r1, [r4, #4] ; \
+        mov r6, r0 ; \
+        mov r12, r1 ; \
+        op(r0, r1, r0, r1, r2, r3) ; \
+        str r0, [r4, #0] ; \
+        str r1, [r4, #4] ; \
+        msr PRIMASK, r5 ; \
+        mov r0, r6 ; \
+        mov r1, r12 ; \
+        pop {r4, r5, r6, pc}
+#else
 #define SYNC_OP_8(op) \
         .p2align 2 ; \
         .thumb ; \
@@ -47,6 +86,7 @@
         bne LOCAL_LABEL(tryatomic_ ## op) ; \
         dmb ; \
         pop {r4, r5, r6, pc}
+#endif
 
 #define MINMAX_4(rD, rN, rM, cmp_kind) \
         cmp rN, rM ; \
Index: lib/builtins/arm/sync_fetch_and_add_4.S
===================================================================
--- lib/builtins/arm/sync_fetch_and_add_4.S
+++ lib/builtins/arm/sync_fetch_and_add_4.S
@@ -15,7 +15,7 @@
 #include "sync-ops.h"
 
 /* "adds" is 2 bytes shorter than "add". */
-#define add_4(rD, rN, rM)  add rD, rN, rM
+#define add_4(rD, rN, rM)  adds rD, rN, rM
 
 SYNC_OP_4(add_4)
 
Index: lib/builtins/arm/sync_fetch_and_add_8.S
===================================================================
--- lib/builtins/arm/sync_fetch_and_add_8.S
+++ lib/builtins/arm/sync_fetch_and_add_8.S
@@ -14,13 +14,11 @@
 
 #include "sync-ops.h"
 
-#if __ARM_ARCH_PROFILE != 'M'
 #define add_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI) \
     adds rD_LO, rN_LO, rM_LO ; \
-    adc rD_HI, rN_HI, rM_HI
+    adcs rD_HI, rN_HI, rM_HI
 
 SYNC_OP_8(add_8)
-#endif
 
 NO_EXEC_STACK_DIRECTIVE
 
Index: lib/builtins/arm/sync_fetch_and_and_4.S
===================================================================
--- lib/builtins/arm/sync_fetch_and_and_4.S
+++ lib/builtins/arm/sync_fetch_and_and_4.S
@@ -14,7 +14,7 @@
 
 #include "sync-ops.h"
 
-#define and_4(rD, rN, rM)  and rD, rN, rM
+#define and_4(rD, rN, rM)  ands rD, rN, rM
 
 SYNC_OP_4(and_4)
 
Index: lib/builtins/arm/sync_fetch_and_and_8.S
===================================================================
--- lib/builtins/arm/sync_fetch_and_and_8.S
+++ lib/builtins/arm/sync_fetch_and_and_8.S
@@ -14,13 +14,11 @@
 
 #include "sync-ops.h"
 
-#if __ARM_ARCH_PROFILE != 'M'
 #define and_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI) \
-    and rD_LO, rN_LO, rM_LO ; \
-    and rD_HI, rN_HI, rM_HI
+    ands rD_LO, rN_LO, rM_LO ; \
+    ands rD_HI, rN_HI, rM_HI
 
 SYNC_OP_8(and_8)
-#endif
 
 NO_EXEC_STACK_DIRECTIVE
 
Index: lib/builtins/arm/sync_fetch_and_nand_4.S
===================================================================
--- lib/builtins/arm/sync_fetch_and_nand_4.S
+++ lib/builtins/arm/sync_fetch_and_nand_4.S
@@ -14,7 +14,7 @@
 
 #include "sync-ops.h"
 
-#define nand_4(rD, rN, rM)  bic rD, rN, rM
+#define nand_4(rD, rN, rM)  bics rD, rN, rM
 
 SYNC_OP_4(nand_4)
 
Index: lib/builtins/arm/sync_fetch_and_nand_8.S
===================================================================
--- lib/builtins/arm/sync_fetch_and_nand_8.S
+++ lib/builtins/arm/sync_fetch_and_nand_8.S
@@ -14,13 +14,11 @@
 
 #include "sync-ops.h"
 
-#if __ARM_ARCH_PROFILE != 'M'
 #define nand_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI) \
-    bic rD_LO, rN_LO, rM_LO ; \
-    bic rD_HI, rN_HI, rM_HI
+    bics rD_LO, rN_LO, rM_LO ; \
+    bics rD_HI, rN_HI, rM_HI
 
 SYNC_OP_8(nand_8)
-#endif
 
 NO_EXEC_STACK_DIRECTIVE
 
Index: lib/builtins/arm/sync_fetch_and_or_4.S
===================================================================
--- lib/builtins/arm/sync_fetch_and_or_4.S
+++ lib/builtins/arm/sync_fetch_and_or_4.S
@@ -14,7 +14,7 @@
 
 #include "sync-ops.h"
 
-#define or_4(rD, rN, rM)  orr rD, rN, rM
+#define or_4(rD, rN, rM)  orrs rD, rN, rM
 
 SYNC_OP_4(or_4)
 
Index: lib/builtins/arm/sync_fetch_and_or_8.S
===================================================================
--- lib/builtins/arm/sync_fetch_and_or_8.S
+++ lib/builtins/arm/sync_fetch_and_or_8.S
@@ -14,13 +14,11 @@
 
 #include "sync-ops.h"
 
-#if __ARM_ARCH_PROFILE != 'M'
 #define or_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI) \
-    orr rD_LO, rN_LO, rM_LO ; \
-    orr rD_HI, rN_HI, rM_HI
+    orrs rD_LO, rN_LO, rM_LO ; \
+    orrs rD_HI, rN_HI, rM_HI
 
 SYNC_OP_8(or_8)
-#endif
 
 NO_EXEC_STACK_DIRECTIVE
 
Index: lib/builtins/arm/sync_fetch_and_sub_4.S
===================================================================
--- lib/builtins/arm/sync_fetch_and_sub_4.S
+++ lib/builtins/arm/sync_fetch_and_sub_4.S
@@ -15,7 +15,7 @@
 #include "sync-ops.h"
 
 /* "subs" is 2 bytes shorter than "sub". */
-#define sub_4(rD, rN, rM)  sub rD, rN, rM
+#define sub_4(rD, rN, rM)  subs rD, rN, rM
 
 SYNC_OP_4(sub_4)
 
Index: lib/builtins/arm/sync_fetch_and_sub_8.S
===================================================================
--- lib/builtins/arm/sync_fetch_and_sub_8.S
+++ lib/builtins/arm/sync_fetch_and_sub_8.S
@@ -14,13 +14,11 @@
 
 #include "sync-ops.h"
 
-#if __ARM_ARCH_PROFILE != 'M'
 #define sub_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI) \
     subs rD_LO, rN_LO, rM_LO ; \
-    sbc rD_HI, rN_HI, rM_HI
+    sbcs rD_HI, rN_HI, rM_HI
 
 SYNC_OP_8(sub_8)
-#endif
 
 NO_EXEC_STACK_DIRECTIVE
 
Index: lib/builtins/arm/sync_fetch_and_xor_4.S
===================================================================
--- lib/builtins/arm/sync_fetch_and_xor_4.S
+++ lib/builtins/arm/sync_fetch_and_xor_4.S
@@ -14,7 +14,7 @@
 
 #include "sync-ops.h"
 
-#define xor_4(rD, rN, rM)  eor rD, rN, rM
+#define xor_4(rD, rN, rM)  eors rD, rN, rM
 
 SYNC_OP_4(xor_4)
 
Index: lib/builtins/arm/sync_fetch_and_xor_8.S
===================================================================
--- lib/builtins/arm/sync_fetch_and_xor_8.S
+++ lib/builtins/arm/sync_fetch_and_xor_8.S
@@ -14,13 +14,11 @@
 
 #include "sync-ops.h"
 
-#if __ARM_ARCH_PROFILE != 'M'
 #define xor_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI) \
-    eor rD_LO, rN_LO, rM_LO ; \
-    eor rD_HI, rN_HI, rM_HI
+    eors rD_LO, rN_LO, rM_LO ; \
+    eors rD_HI, rN_HI, rM_HI
 
 SYNC_OP_8(xor_8)
-#endif
 
 NO_EXEC_STACK_DIRECTIVE