要使用sftp功能，从网上找了QSsh-master代码在centos上编译，结果qt报错
../../QSsh-master/src/3rdparty/botan/botan.cpp:1127:43: error: impossible constraint in 'asm'
从网上找了没有找到解决办法。就改用libssh2来实现sftp功能在centos6.8上的交叉编译环上编译openssl，执行./configure 失败报错Can't locate IPC/Cmd.pm，百度了下
报错原因：缺少IPC/Cmd.pm模块
解决方法：
安装perl-CPAN，
yum install -y perl-CPAN
嫌弃安装软件麻烦，决定把交叉编译环境整到ubuntu 16 32位上。
新建虚拟机，装好系统 ，安装qt环境，编译一个嵌入式程序测试，报错找不到编译器，我设置了环境变量PATH,但就是报错，又百度，说编译其他平台程序 ，环境变量设置是修改/etc/environment文件，后加入后，终于可以编译了。
接着要交叉编译openssl , libssh2 两个
下载源码，先是编译openssl,
先apt-get install libssl-dev
否则报错configure: error: OpenSSL Crypto library not found
./Configure linux-armv4 --cross-compile-prefix=arm-hisiv400-linux- --prefix=/home/mission/sftp/openssl-3.0.1
第一个linux-armv4是嵌入式平台
--cross-compile-prefix是加上交叉编译的前缀，makefile则会自动变成arm-hisiv400-linux-g++等，
且产生的makefile也是能直接使用。
编译好后，再编译libssh2
./configure ?CC=arm-hisiv400-linux-g++ --prefix=/home/mission/sftp/libssh2-1.10.0 指定编译器后，报错?
checking whether we are cross compiling... configure: error: in `/home/mission/sftp/libssh2-1.10.0/libssh2-1.10.0':
configure: error: cannot run C compiled programs.
If you meant to cross compile, use `--host'.
后改成./configure ?CC=arm-hisiv400-linux-g++ --prefix=/home/mission/sftp/libssh2-1.10.0 --host=arm-linux
又报错
configure: ERROR: No openssl crypto library found!
No libgcrypt crypto library found!
No mbedtls crypto library found!
No wincng crypto library found!
Specify --with-crypto=$backend and/or the neccessary library search prefix.
Known crypto backends: auto, openssl, libgcrypt, mbedtls, wincng
configure: error: Required dependencies are missing!
又改./configure ?CC=arm-hisiv400-linux-g++ --prefix=/home/mission/sftp/libssh2-1.10.0 --host=arm-linux --with-libssl-prefix=/home/mission/sftp/openssl-3.0.1
加上了自己编译的openssl的路径，终于好了。
但make时又报错。找不到libatomic.so，把交叉编译环境里的这个库找到放到openssl的库一起，再编译
/opt/hisi-linux/x86-arm/arm-hisiv400-linux/bin/../lib/gcc/arm-hisiv400-linux-gnueabi/4.8.3/../../../../arm-hisiv400-linux-gnueabi/bin/ld: warning: libssl.so.3, needed by ../src/.libs/libssh2.so, not found (try using -rpath or -rpath-link)
/opt/hisi-linux/x86-arm/arm-hisiv400-linux/bin/../lib/gcc/arm-hisiv400-linux-gnueabi/4.8.3/../../../../arm-hisiv400-linux-gnueabi/bin/ld: warning: libcrypto.so.3, needed by ../src/.libs/libssh2.so, not found (try using -rpath or -rpath-link)
../src/.libs/libssh2.so: undefined reference to `EVP_MD_CTX_free@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `EVP_ripemd160@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `EVP_PKEY_derive@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `EVP_PKEY_get1_EC_KEY@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `EVP_PKEY_get1_DSA@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `BIO_ctrl@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `EVP_PKEY_free@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `RSA_get0_factors@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `HMAC_Final@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `EVP_PKEY_CTX_new_id@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `EVP_sha256@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `EVP_DigestSignInit@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `ECDSA_SIG_set0@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `EC_KEY_get0_public_key@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `ENGINE_load_builtin_engines@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `EC_KEY_free@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `BN_mod_exp@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `EC_KEY_new_by_curve_name@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `EVP_PKEY_keygen_init@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `EVP_PKEY_get_raw_private_key@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `EVP_sha1@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `ECDSA_SIG_free@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `EVP_DigestInit@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `RSA_size@OPENSSL_3.0.0'
../src/.libs/libssh2.so: undefined reference to `EVP_PKEY_derive_init@OPENSSL_3.0.0'
参考网上别人的应该是没有加上库路径
又改./configure ?CC=arm-hisiv400-linux-gcc --prefix=/home/mission/sftp/libssh2-1.10.0 --host=arm-linux --with-libssl-prefix=/home/mission/sftp/openssl-3.0.1 LDFLAGS="-Wl,-rpath-link,/home/mission/sftp/openssl-3.0.1/lib"，终于好了
