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

fusl/arch/arm/src/find_exidx.c

+#define _GNU_SOURCE
+#include <link.h>
+#include <stdint.h>
+
+struct find_exidx_data {
+        uintptr_t pc, exidx_start;
+        int exidx_len;
+};
+
+static int find_exidx(struct dl_phdr_info *info, size_t size, void *ptr)
+{
+        struct find_exidx_data *data = ptr;
+        const ElfW(Phdr) *phdr = info->dlpi_phdr;
+        uintptr_t addr, exidx_start = 0;
+        int i, match = 0, exidx_len = 0;
+
+        for (i = info->dlpi_phnum; i > 0; i--, phdr++) {
+                addr = info->dlpi_addr + phdr->p_vaddr;
+                switch (phdr->p_type) {
+                case PT_LOAD:
+                        match |= data->pc >= addr && data->pc < addr + phdr->p_memsz;
+                        break;
+                case PT_ARM_EXIDX:
+                        exidx_start = addr;
+                        exidx_len = phdr->p_memsz;
+                        break;
+                }
+        }
+        data->exidx_start = exidx_start;
+        data->exidx_len = exidx_len;
+        return match;
+}
+
+uintptr_t __gnu_Unwind_Find_exidx(uintptr_t pc, int *pcount)
+{
+        struct find_exidx_data data;
+        data.pc = pc;
+        if (dl_iterate_phdr(find_exidx, &data) <= 0)
+                return 0;
+        *pcount = data.exidx_len / 8;
+        return data.exidx_start;
+}