Add a "fork" of musl as //fusl.

fusl/arch/arm/atomic.h

+#ifndef _INTERNAL_ATOMIC_H
+#define _INTERNAL_ATOMIC_H
+
+#include <stdint.h>
+
+static inline int a_ctz_l(unsigned long x)
+{
+        static const char debruijn32[32] = {
+                0, 1, 23, 2, 29, 24, 19, 3, 30, 27, 25, 11, 20, 8, 4, 13,
+                31, 22, 28, 18, 26, 10, 7, 12, 21, 17, 9, 6, 16, 5, 15, 14
+        };
+        return debruijn32[(x&-x)*0x076be629 >> 27];
+}
+
+static inline int a_ctz_64(uint64_t x)
+{
+        uint32_t y = x;
+        if (!y) {
+                y = x>>32;
+                return 32 + a_ctz_l(y);
+        }
+        return a_ctz_l(y);
+}
+
+#if __ARM_ARCH_7A__ || __ARM_ARCH_7R__ ||  __ARM_ARCH >= 7
+
+static inline void a_barrier()
+{
+        __asm__ __volatile__("dmb ish");
+}
+
+static inline int a_cas(volatile int *p, int t, int s)
+{
+        int old;
+        __asm__ __volatile__(
+                "       dmb ish\n"
+                "1:     ldrex %0,%3\n"
+                "       cmp %0,%1\n"
+                "       bne 1f\n"
+                "       strex %0,%2,%3\n"
+                "       cmp %0, #0\n"
+                "       bne 1b\n"
+                "       mov %0, %1\n"
+                "1:     dmb ish\n"
+                : "=&r"(old)
+                : "r"(t), "r"(s), "Q"(*p)
+                : "memory", "cc" );
+        return old;
+}
+
+static inline int a_swap(volatile int *x, int v)
+{
+        int old, tmp;
+        __asm__ __volatile__(
+                "       dmb ish\n"
+                "1:     ldrex %0,%3\n"
+                "       strex %1,%2,%3\n"
+                "       cmp %1, #0\n"
+                "       bne 1b\n"
+                "       dmb ish\n"
+                : "=&r"(old), "=&r"(tmp)
+                : "r"(v), "Q"(*x)
+                : "memory", "cc" );
+        return old;
+}
+
+static inline int a_fetch_add(volatile int *x, int v)
+{
+        int old, tmp;
+        __asm__ __volatile__(
+                "       dmb ish\n"
+                "1:     ldrex %0,%3\n"
+                "       add %0,%0,%2\n"
+                "       strex %1,%0,%3\n"
+                "       cmp %1, #0\n"
+                "       bne 1b\n"
+                "       dmb ish\n"
+                : "=&r"(old), "=&r"(tmp)
+                : "r"(v), "Q"(*x)
+                : "memory", "cc" );
+        return old-v;
+}
+
+static inline void a_inc(volatile int *x)
+{
+        int tmp, tmp2;
+        __asm__ __volatile__(
+                "       dmb ish\n"
+                "1:     ldrex %0,%2\n"
+                "       add %0,%0,#1\n"
+                "       strex %1,%0,%2\n"
+                "       cmp %1, #0\n"
+                "       bne 1b\n"
+                "       dmb ish\n"
+                : "=&r"(tmp), "=&r"(tmp2)
+                : "Q"(*x)
+                : "memory", "cc" );
+}
+
+static inline void a_dec(volatile int *x)
+{
+        int tmp, tmp2;
+        __asm__ __volatile__(
+                "       dmb ish\n"
+                "1:     ldrex %0,%2\n"
+                "       sub %0,%0,#1\n"
+                "       strex %1,%0,%2\n"
+                "       cmp %1, #0\n"
+                "       bne 1b\n"
+                "       dmb ish\n"
+                : "=&r"(tmp), "=&r"(tmp2)
+                : "Q"(*x)
+                : "memory", "cc" );
+}
+
+static inline void a_and(volatile int *x, int v)
+{
+        int tmp, tmp2;
+        __asm__ __volatile__(
+                "       dmb ish\n"
+                "1:     ldrex %0,%3\n"
+                "       and %0,%0,%2\n"
+                "       strex %1,%0,%3\n"
+                "       cmp %1, #0\n"
+                "       bne 1b\n"
+                "       dmb ish\n"
+                : "=&r"(tmp), "=&r"(tmp2)
+                : "r"(v), "Q"(*x)
+                : "memory", "cc" );
+}
+
+static inline void a_or(volatile int *x, int v)
+{
+        int tmp, tmp2;
+        __asm__ __volatile__(
+                "       dmb ish\n"
+                "1:     ldrex %0,%3\n"
+                "       orr %0,%0,%2\n"
+                "       strex %1,%0,%3\n"
+                "       cmp %1, #0\n"
+                "       bne 1b\n"
+                "       dmb ish\n"
+                : "=&r"(tmp), "=&r"(tmp2)
+                : "r"(v), "Q"(*x)
+                : "memory", "cc" );
+}
+
+static inline void a_store(volatile int *p, int x)
+{
+        __asm__ __volatile__(
+                "       dmb ish\n"
+                "       str %1,%0\n"
+                "       dmb ish\n"
+                : "=m"(*p)
+                : "r"(x)
+                : "memory", "cc" );
+}
+
+#else
+
+int __a_cas(int, int, volatile int *) __attribute__((__visibility__("hidden")));
+#define __k_cas __a_cas
+
+static inline void a_barrier()
+{
+        __asm__ __volatile__("bl __a_barrier"
+                : : : "memory", "cc", "ip", "lr" );
+}
+
+static inline int a_cas(volatile int *p, int t, int s)
+{
+        int old;
+        for (;;) {
+                if (!__k_cas(t, s, p))
+                        return t;
+                if ((old=*p) != t)
+                        return old;
+        }
+}
+
+static inline int a_swap(volatile int *x, int v)
+{
+        int old;
+        do old = *x;
+        while (__k_cas(old, v, x));
+        return old;
+}
+
+static inline int a_fetch_add(volatile int *x, int v)
+{
+        int old;
+        do old = *x;
+        while (__k_cas(old, old+v, x));
+        return old;
+}
+
+static inline void a_inc(volatile int *x)
+{
+        a_fetch_add(x, 1);
+}
+
+static inline void a_dec(volatile int *x)
+{
+        a_fetch_add(x, -1);
+}
+
+static inline void a_store(volatile int *p, int x)
+{
+        a_barrier();
+        *p = x;
+        a_barrier();
+}
+
+static inline void a_and(volatile int *p, int v)
+{
+        int old;
+        do old = *p;
+        while (__k_cas(old, old&v, p));
+}
+
+static inline void a_or(volatile int *p, int v)
+{
+        int old;
+        do old = *p;
+        while (__k_cas(old, old|v, p));
+}
+
+#endif
+
+static inline void *a_cas_p(volatile void *p, void *t, void *s)
+{
+        return (void *)a_cas(p, (int)t, (int)s);
+}
+
+#define a_spin a_barrier
+
+static inline void a_crash()
+{
+        *(volatile char *)0=0;
+}
+
+static inline void a_or_l(volatile void *p, long v)
+{
+        a_or(p, v);
+}
+
+static inline void a_and_64(volatile uint64_t *p, uint64_t v)
+{
+        union { uint64_t v; uint32_t r[2]; } u = { v };
+        a_and((int *)p, u.r[0]);
+        a_and((int *)p+1, u.r[1]);
+}
+
+static inline void a_or_64(volatile uint64_t *p, uint64_t v)
+{
+        union { uint64_t v; uint32_t r[2]; } u = { v };
+        a_or((int *)p, u.r[0]);
+        a_or((int *)p+1, u.r[1]);
+}
+
+#endif