g ++搜索/lib/../lib/，然后/ lib / [英] g++ searches /lib/../lib/, then /lib/

问题描述

根据 g ++ -print-search-dirs ，我的C ++编译器正在许多目录中搜索库，包括...

• / lib /../ lib /：


• / usr / lib /../ lib /：


• / lib /：


• / usr / lib /

code> / lib /../ lib / 看起来与 / lib / — lib的父母将有一个名为lib的孩子，那人的父亲的儿子是我父亲的儿子的儿子等等。这同样适用于 / usr / lib /../ lib / 和 / usr / lib /

1. 是否有一些原因，可能与符号链接有关，g ++应该配置为同时搜索​​ / lib /../ lib / 和 / lib / ？




2. 如果这是不必要的冗余，那么如何解决它？

重要的是，这是在未修改的Ubuntu 9.04安装中观察到的。

编辑：更多信息

结果来自执行 g ++ -print-search-dirs 没有其他开关，来自bash shell。

LIBRARY_PATH和LPATH都不是从 printenv 输出的，而是 echo $ LPATH 和 echo LIBRARY_PATH return blank lines。

解决方案

尝试一个答案（我从几分钟的时间内收集了 gcc.c 驱动程序源代码和Makefile环境）。

这些路径是在运行时从以下位置构建的：



1. GCC exec前缀（参见 GCC_EXEC_PREFIX 的gnsite.ualberta.ca/Documentation/Gnu/gcc-3.0.2/html_node/gcc_53.htmlrel =nofollow noreferrer> GCC文档。 ） $ LIBRARY_PATH 环境变量


2. $ LPATH 环境变量（对待 $ LIBRARY_PATH ）


3. 任何传递给 -B 命令行开关


4. 标准可执行文件前缀（如编译期间指定的那样）


5. ldir prefix

最后一个（tooldir前缀）通常被定义为相对路径：
从gcc的 Makefile.in

 ＃编译器查找库等的目录
 libsubdir = $（libdir）/ gcc / $（target_noncanonical）/ $（version）
＃编译器找到可执行文件的目录
 libexecsubdir = $（libexecdir）/ gcc / $（target_noncanonical）/ $ （版本）
＃用于在gcc.o中生成一个相对$（gcc_tooldir）
 unlibsubdir = ../../ .. 
 .... 
＃作为编译标志，因此它们将tooldir基础前缀
＃定义为../../../../，并将库搜索前缀中的一个定义为../../../ 
＃这些获得PREFIX追加，然后机器为其构建的gcc 
＃ie ie484-linux-gnu，得到如下所示：
＃/ usr / lib / gcc / i486-linux-gnu /4.2.3/../../../../i486-linux-gnu/lib/../lib/ 
 DRIVER_DEFINES = \ 
 -DSTANDARD_STARTFILE_PREFIX = \$（ unlibsubdir）/ \\ 
 -DTO OLDIR_BASE_PREFIX = \$（unlibsubdir）/../ \\ 
  

然而，这些是针对编译器版本特定的路径。你的例子很可能受上面列出的环境变量（ LIBRARY_PATH ， LPATH ）影响

According to g++ -print-search-dirs my C++ compiler is searching for libraries in many directories, including ...

• /lib/../lib/:
• /usr/lib/../lib/:
• /lib/:
• /usr/lib/

Naively, /lib/../lib/ would appear to be the same directory as /lib/ — lib's parent will have a child named lib, "that man's father's son is my father's son's son" and all that. The same holds for /usr/lib/../lib/ and /usr/lib/

1. Is there some reason, perhaps having to do with symbolic links, that g++ ought to be configured to search both /lib/../lib/ and /lib/?

2. If this is unnecessary redundancy, how would one go about fixing it?

If it matters, this was observed on an unmodified install of Ubuntu 9.04.

Edit: More information.

The results are from executing g++ -print-search-dirs with no other switches, from a bash shell.

Neither LIBRARY_PATH nor LPATH are output from printenv, and both echo $LPATH and echo LIBRARY_PATH return blank lines.

解决方案

An attempt at an answer (which I gathered from a few minutes of looking at the gcc.c driver source and the Makefile environment).

These paths are constructed in runtime from:

1. GCC exec prefix (see GCC documentation on GCC_EXEC_PREFIX)
2. The $LIBRARY_PATH environment variable
3. The $LPATH environment variable (which is treated like $LIBRARY_PATH)
4. Any values passed to -B command-line switch
5. Standard executable prefixes (as specified during compilation time)
6. Tooldir prefix

The last one (tooldir prefix) is usually defined to be a relative path: From gcc's Makefile.in

# Directory in which the compiler finds libraries etc.
libsubdir = $(libdir)/gcc/$(target_noncanonical)/$(version)
# Directory in which the compiler finds executables
libexecsubdir = $(libexecdir)/gcc/$(target_noncanonical)/$(version)
# Used to produce a relative $(gcc_tooldir) in gcc.o
unlibsubdir = ../../..
....
# These go as compilation flags, so they define the tooldir base prefix
# as ../../../../, and the one of the library search prefixes as ../../../
# These get PREFIX appended, and then machine for which gcc is built
# i.e i484-linux-gnu, to get something like: 
# /usr/lib/gcc/i486-linux-gnu/4.2.3/../../../../i486-linux-gnu/lib/../lib/
DRIVER_DEFINES = \
-DSTANDARD_STARTFILE_PREFIX=\"$(unlibsubdir)/\" \
-DTOOLDIR_BASE_PREFIX=\"$(unlibsubdir)/../\" \

However, these are for compiler-version specific paths. Your examples are likely affected by the environment variables that I've listed above (LIBRARY_PATH, LPATH)

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