Linux中的ldd命令和pvs命令

发布时间：2014-09-05 16:10:36作者：知识屋

Linux中的ldd命令和pvs命令

ldd命令用于判断某个可执行的 binary 档案含有什么动态函式库。

参数说明：

--version　　打印ldd的版本号

-v --verbose　　打印所有信息，例如包括符号的版本信息

-d --data-relocs　　执行符号重部署，并报告缺少的目标对象（只对ELF格式适用）

-r --function-relocs　　对目标对象和函数执行重新部署，并报告缺少的目标对象和函数（只对ELF格式适用） www.zhishiwu.com

--help 用法信息

如果命令行中给定的库名字包含'/'，这个程序的libc5版本将使用它作为库名字；否则它将在标准位置搜索库。运行一个当前目录下的共享库，加前缀"./"。

错误:

ldd不能工作在a.out格式的共享库上。

ldd不能工作在一些非常老的a.out程序上，这些程序在支持ldd的编译器发行前已经创建。如果你在这种类型的程序上使用ldd，程序将尝试argc = 0的运行方式，其结果不可预知。

例如：

ldd /bin/bash

但是ldd本身不是一个程序，而仅是一个shell脚本：

$ which ldd

/usr/bin/ldd

$ file /usr/bin/ldd

/usr/bin/ldd: Bourne-Again shell script text executable

ldd命令其实是依靠设置一些环境变量而实现的(也就是说ldd的作用只是设置一些环境变量的值)

如:LD_TRACE_LOADED_OBJECTS

只要设置其值非空即可。

$ export LD_TRACE_LOADED_OBJECTS=1

$ ls /usr

linux-gate.so.1 => (0xb7fac000)

librt.so.1 => /lib/tls/i686/cmov/librt.so.1 (0xb7f93000)

libselinux.so.1 => /lib/libselinux.so.1 (0xb7f79000)

libacl.so.1 => /lib/libacl.so.1 (0xb7f70000)

libc.so.6 => /lib/tls/i686/cmov/libc.so.6 (0xb7e0d000)

libpthread.so.0 => /lib/tls/i686/cmov/libpthread.so.0 (0xb7df4000)

/lib/ld-linux.so.2 (0xb7fad000) www.zhishiwu.com

libdl.so.2 => /lib/tls/i686/cmov/libdl.so.2 (0xb7df0000)

libattr.so.1 => /lib/libattr.so.1 (0xb7dea000)

撤销该环境变量，ls即又可以恢复正常使用：

$ unset LD_TRACE_LOADED_OBJECTS

$ ls /usr/

bin games include lib lib32 lib64 local sbin share src X11R6

更多的环境变量：

1、LD_TRACE_LOADED_OBJECTS

2、LD_WARN

3、LD_BIND_NOW

4、LD_LIBRARY_VERSION

5、LD_VERBOSE

6、LD_DEBUG

ldd默认开启的环境变量是：LD_TRACE_LOADED_OBJECTS=1

其他的变量(和值)分别对应一些选项：

-d, --data-relocs -> LD_WARN=yes

-r, --function-relocs ->LD_WARN和LD_BIND_NOW=yes

-u, --unused -> LD_DEBUG="unused"

-v, --verbose -> LD_VERBOSE=yes www.zhishiwu.com

LD_TRACE_LOADED_OBJECTS为必要环境变量，其他视具体情况。

ldd命令的本质是执行了:/lib/ld-linux.so.*

我们可以从以上的内容中(ls /usr中)发现：/lib/ld-linux.so.2 (0xb7fad000)。

$ ls -l /lib/ld-linux.so.*

lrwxrwxrwx 1 root root 9 2009-09-05 22:54 /lib/ld-linux.so.2 -> ld-2.9.so

刚编译后的文件可能是:/lib/ld.so。如果是libc5则是/lib/ld-linux.so.1, 而glibc2应该是/lib/ld-linux.so.2。

$ /lib/ld-linux.so.2 --list /bin/ls

linux-gate.so.1 => (0xb8050000)

librt.so.1 => /lib/tls/i686/cmov/librt.so.1 (0xb8037000)

libselinux.so.1 => /lib/libselinux.so.1 (0xb801d000)

libacl.so.1 => /lib/libacl.so.1 (0xb8014000)

libc.so.6 => /lib/tls/i686/cmov/libc.so.6 (0xb7eb1000)

libpthread.so.0 => /lib/tls/i686/cmov/libpthread.so.0 (0xb7e98000)

/lib/ld-linux.so.2 (0xb8051000)

libdl.so.2 => /lib/tls/i686/cmov/libdl.so.2 (0xb7e94000)

libattr.so.1 => /lib/libattr.so.1 (0xb7e8e000)

我们可以看到以上等同于ldd ls。

ldd可以获得的共享库文件，其实是通过读取ldconfig命令组建起来的文件(/etc/ld.so.cache)。

默认的共享库文件搜索/lib优先于/usr/lib，而且也只有这个2个目录。如果想要加入其他路径，则需要通过ldconfig命令配置相关文件。

一般ld-linux.so会按照以下顺序搜索共享库:

1、DT_RPATH或DT_RUNPATH段

2、环境变量LD_LIBRARY_PATH

3、/etc/ld.so.cache文件中的路径，但如果可执行程序在连接时候添加了-z nodeflib选项，则跳过。

4、默认路径/lib和/usr/lib，但如果添加了-z nodeflib，则跳过。

PVS

Display the internal version information of dynamic objects within an ELF file. Commonly these files are dynamic executables and shared objects, and possibly relocatable objects. This version information can fall into one of the following two categories: www.zhishiwu.com

Version definitions described the interface made available by an ELF file. Each version definition is associated to a set of global symbols provided by the file.

Version dependencies describe the binding requirements of dynamic objects on the version definition of any shared object dependencies. When a dynamic object is built with a shared object, the link-editor records information within the dynamic object indicating that the shared object is a dependency.

Syntax

pvs [-d] [-l] [-n] [-o] [-r] [-s] [-v] [-N name] file

-d Print version definition information.

-l When used with the -s option, print any symbols that have been reduced from global to local binding due to versioning. By convention, these symbol entries are located in the .symtab section, and fall between the FILE symbol representing the output file, and the FILE symbol representing the first input file used to generate the output file. These reduced symbol entries are assigned the fabricated version definition _REDUCED_. No

reduced symbols will be printed if the file has been stripped, or if the symbol

entry convention cannot be determined.

-n Normalize version definition information. By default, all version definitions within the object are displayed. However, version definitions may inherit other version definitions, and under normalization only the head of each inheritance list is displayed.

-o Create one-line version definition output. By default, file, version definitions, and any symbol output is indented to ease human inspection. This option prefixes each output line with the file and version definition name and may be more useful for analysis with automated tools. www.zhishiwu.com

-r Print version dependency (requirements) information.

-s Print the symbols associated with each version definition. Any data symbols are accompanied with the size, in bytes, of the data item.

-v Verbose output. Indicates any weak version definitions, and any version definition inheritance. When used with the -N and -d options, the inheritance of the base version definition is also shown. When used with the -s option, the version symbol definition is also shown.

-N name Print only the information for the given version definition name and any of its inherited version definitions (when used with the -d option), or for the given dependency file name (when used with the -r option).

file The ELF file about which internal version information is displayed.

Examples

pvs /usr/lib/64/libc.so.1

作者 icybay

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