configure: error: mod_so has been requested but cannot be built on your system
openwrt 交叉編譯 apache ，
configure 添加 --enable-so 選項後報錯信息如下：
configure: error: mod_so has been requested but cannot be built on your system
原因分析 ：
在編譯目錄查找打印上面錯誤的位置，grep “mod_so has been requested but cannot be built on your system” configure -n
httpd-2.4.28# grep "mod_so has been requested but cannot be built on your system" configure -n
13655: as_fn_error $? "mod_so has been requested but cannot be built on your system" "$LINENO" 5
在 configure 文件的 第 13655 行：查看其上下文：
cat confdefs.h - <<_ACEOF >conftest.$ac_ext
/* end confdefs.h. */
#include <apr.h>
#if APR_HAS_DSO
YES_IS_DEFINED
#endif
_ACEOF
if (eval "$ac_cpp conftest.$ac_ext") 2>&5 |
$EGREP "YES_IS_DEFINED" >/dev/null 2>&1; then :
ac_cv_define_APR_HAS_DSO=yes
else
ac_cv_define_APR_HAS_DSO=no
fi
rm -f conftest*
CPPFLAGS=$apr_old_cppflags
case "x$enable_so" in
"xyes")
if test $ac_cv_define_APR_HAS_DSO = "no"; then
as_fn_error $? "mod_so has been requested but cannot be built on your system" "$LINENO" 5
fi
;;
可知 configure 腳本檢查了 APR_HAS_DSO 宏定義，沒有定義APR_HAS_DSO 時就會報以上錯誤，
APR_HAS_DSO 位於 apr.h 中，來自 libapr 。
檢查 libapr 的 編譯選項： 位於 openwrt\feeds\packages\libs\apr\Makefile
CONFIGURE_ARGS += \
--with-devrandom=/dev/urandom \
--disable-dso \
$(call autoconf_bool,CONFIG_IPV6,ipv6)
openwrt 編譯 libapr 時 開啓了 --disable-dso 導致 APR_HAS_DSO 宏未定義
解決辦法：
修改 openwrt\feeds\packages\libs\apr\Makefile ， 把 --disable-dso 選項去掉
CONFIGURE_ARGS += \
--with-devrandom=/dev/urandom \
$(call autoconf_bool,CONFIG_IPV6,ipv6)
從新編譯libapr 後再編譯 apache