链接器总是选择系统libsasldb.so而不是LD_LIBRARY_PATH提供的系统

Question

我在基于heroku的环境中运行，因此不允许在系统空间中安装软件包。为了解决这个问题，他们将安装到/app/.apt并更新LD_LIBRARY_PATH以反映这一点。

我正在尝试使用cyrus-sasl2，所以在那里安装并看到它已安装，但是当我尝试使用这个库时，我发现它无法接收gssapiv2，它也安装在同一个位置。

使用LD_DEBUG=all运行代码我看到一些有趣的东西

file=/usr/lib/x86_64-linux-gnu/sasl2/libsasldb.so [0];  dynamically loaded by /app/.apt/usr/lib/x86_64-linux-gnu/libsasl2.so.2 [0]

通常情况下，我看到图书馆会进行搜索，但这总是会占用系统并且不会执行搜索。我期待的东西如下

  1673:
  1673:     file=libsasl2.so.2 [0];  needed by /app/.heroku/python/lib/python2.7/site-packages/sasl/saslwrapper.so [0]
  1673:     find library=libsasl2.so.2 [0]; searching
  1673:      search path=/app/.heroku/vendor/lib:/app/.heroku/python/lib:/app/.apt/usr/lib/x86_64-linux-gnu:/app/.apt/usr/lib:tls/x86_64:tls:x86_64:                (LD_LIBRARY_PATH)
  1673:       trying file=/app/.heroku/vendor/lib/libsasl2.so.2
  1673:       trying file=/app/.heroku/python/lib/libsasl2.so.2
  1673:       trying file=/app/.apt/usr/lib/x86_64-linux-gnu/libsasl2.so.2

但我不认为在libsasldb.so的情况下。

我的问题是，为什么链接器不会搜索，而是总是使用系统版本？

Answer 1

在上面的例子中，结果是cyrus-sasl使用编译时标志来定义插件目录并将从该路径加载。我重新编译了项目，将插件目录更改为heroku位置，并查看以下系统调用

openat(AT_FDCWD, "/app/.apt/usr/lib/sasl2", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 5
open("/app/.apt/usr/lib/sasl2/libcrammd5.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/libcrammd5.so.2", O_RDONLY|O_CLOEXEC) = 6
open("/app/.apt/usr/lib/sasl2/libdigestmd5.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/libdigestmd5.so.2", O_RDONLY|O_CLOEXEC) = 6
open("/app/.apt/usr/lib/sasl2/libscram.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/libscram.so.2", O_RDONLY|O_CLOEXEC) = 6
open("/app/.apt/usr/lib/sasl2/liblogin.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/liblogin.so.2", O_RDONLY|O_CLOEXEC) = 6
open("/app/.apt/usr/lib/sasl2/libcrammd5.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/libldapdb.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/libanonymous.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/libanonymous.so.2", O_RDONLY|O_CLOEXEC) = 6
open("/app/.apt/usr/lib/sasl2/libplain.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/libplain.so.2", O_RDONLY|O_CLOEXEC) = 6
open("/app/.apt/usr/lib/sasl2/libntlm.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/libntlm.so.2", O_RDONLY|O_CLOEXEC) = 6
open("/app/.apt/usr/lib/sasl2/libntlm.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/libotp.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/libldapdb.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/libldapdb.so.2", O_RDONLY|O_CLOEXEC) = 6
open("/app/.apt/usr/lib/sasl2/libanonymous.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/liblogin.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/libscram.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/libotp.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/libotp.so.2", O_RDONLY|O_CLOEXEC) = 6
open("/app/.apt/usr/lib/sasl2/libdigestmd5.la", O_RDONLY) = 6
open("/app/.apt/usr/lib/sasl2/libplain.la", O_RDONLY) = 6

简而言之，它控制链接本身，这就是链接器从不搜索其他库的原因。