Fix ptrace library build on FreeBSD/x86_64.

Restore FreeBSD _UPT_access_reg() implementation.

src/ptrace/_UPT_access_reg.c

@@ -321,7 +321,7 @@ _UPT_access_reg (unw_addr_space_t as, unw_regnum_t reg, unw_word_t *val,
   Debug (1, "bad register %s [%u] (error: %s)\n", unw_regname(reg), reg, strerror (errno));
   return -UNW_EBADREG;
 }
-#elif HAVE_DECL_PT_GETREGS
+#elif defined(HAVE_DECL_PT_GETREGS) && defined(__linux__)
 # include <sys/user.h>
 
 int
@@ -359,6 +359,44 @@ _UPT_access_reg (unw_addr_space_t as, unw_regnum_t reg, unw_word_t *val,
   Debug (1, "bad register %s [%u] (error: %s)\n", unw_regname(reg), reg, strerror (errno));
   return -UNW_EBADREG;
 }
+
+#elif defined(HAVE_DECL_PT_GETREGS) && defined(__FreeBSD__)
+int
+_UPT_access_reg (unw_addr_space_t as, unw_regnum_t reg, unw_word_t *val,
+                int write, void *arg)
+{
+  struct UPT_info *ui = arg;
+  pid_t pid = ui->pid;
+  gregset_t regs;
+  char *r;
+
+#if UNW_DEBUG
+  Debug(16, "using getregs: reg: %s [%u], val: %lx, write: %u\n", unw_regname(reg), (unsigned) reg, (long) val, write);
+
+  if (write)
+    Debug (16, "%s [%u] <- %lx\n", unw_regname (reg), (unsigned) reg, (long) *val);
+#endif
+
+  if ((unsigned) reg >= ARRAY_SIZE (_UPT_reg_offset))
+    {
+      errno = EINVAL;
+      goto badreg;
+    }
+  r = (char *)&regs + _UPT_reg_offset[reg];
+  if (ptrace(PT_GETREGS, pid, (caddr_t)&regs, 0) == -1)
+    goto badreg;
+  if (write) {
+      memcpy(r, val, sizeof(unw_word_t));
+      if (ptrace(PT_SETREGS, pid, (caddr_t)&regs, 0) == -1)
+        goto badreg;
+  } else
+      memcpy(val, r, sizeof(unw_word_t));
+  return 0;
+
+ badreg:
+  Debug (1, "bad register %s [%u] (error: %s)\n", unw_regname(reg), reg, strerror (errno));
+  return -UNW_EBADREG;
+}
 #else
 #error Port me
 #endif