涨知识了，Linux的ld和ldd一起用，可以帮我们分析运行时加载库文件失败的原因

通常，开发人员和运维人员在处理软件运行时报错找不到依赖库的问题时，可以使用一些工具来跟踪启动加载的过程，比如strace、gdb等。此外，还可以利用ld和ldd命令来帮助分析依赖库的情况，以便更快地解决问题。这些工具可以帮助定位缺少的依赖库，并指导用户采取适当的措施来解决软件运行时的问题。

这里以分析 libmpi_usempif80.so 这个动态库文件，依赖哪些其他动态库，作为问题起因。

首先介绍 ld 命令如何帮我们分析mpi_usempif80 库依赖其他哪些库？mpi_usempif80 库被加载时，会从当前系统的哪些路径下搜索这些库？

#ld -lmpi_usempif08 –verbose

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5.*/.debug_addr 0 : { *(.debug_addr) }.debug_line_str 0 : { *(.debug_line_str) }.debug_loclists 0 : { *(.debug_loclists) }.debug_macro0 : { *(.debug_macro) }.debug_names0 : { *(.debug_names) }.debug_rnglists 0 : { *(.debug_rnglists) }.debug_str_offsets 0 : { *(.debug_str_offsets) }.debug_sup0 : { *(.debug_sup) }.gnu.attributes 0 : { KEEP (*(.gnu.attributes)) }/DISCARD/ : { *(.note.GNU-stack) *(.gnu_debuglink) *(.gnu.lto_*) }}==================================================ld: mode elf_x86_64attempt to open /usr/local/lib/x86_64-linux-gnu/libmpi_usempif08.so failedattempt to open /usr/local/lib/x86_64-linux-gnu/libmpi_usempif08.a failedattempt to open /lib/x86_64-linux-gnu/libmpi_usempif08.so succeeded/lib/x86_64-linux-gnu/libmpi_usempif08.solibmpi_mpifh.so.40 needed by /lib/x86_64-linux-gnu/libmpi_usempif08.soattempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/mpi/fortran/mpif-h/.libs/libmpi_mpifh.so.40 failedattempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/.libs/libmpi_mpifh.so.40 failedattempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libmpi_mpifh.so.40 failedattempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libmpi_mpifh.so.40 failedattempt to open /usr/local/lib/libmpi_mpifh.so.40 failedfound libmpi_mpifh.so.40 at /usr/lib/x86_64-linux-gnu/libmpi_mpifh.so.40libmpi.so.40 needed by /lib/x86_64-linux-gnu/libmpi_usempif08.soattempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/mpi/fortran/mpif-h/.libs/libmpi.so.40 failedattempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/.libs/libmpi.so.40 failedattempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libmpi.so.40 failedattempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libmpi.so.40 failedattempt to open /usr/local/lib/libmpi.so.40 failedfound libmpi.so.40 at /usr/lib/x86_64-linux-gnu/libmpi.so.40libc.so.6 needed by /lib/x86_64-linux-gnu/libmpi_usempif08.soattempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/mpi/fortran/mpif-h/.libs/libc.so.6 failedattempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/.libs/libc.so.6 failedattempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libc.so.6 failedattempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libc.so.6 failedattempt to open /usr/local/lib/libc.so.6 failedattempt to open /usr/lib/x86_64-linux-gnu/fortran/gfortran/libc.so.6 failedattempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libc.so.6 failedattempt to open /usr/local/lib/x86_64-linux-gnu/libc.so.6 failedattempt to open /usr/local/lib/x86_64-linux-gnu/libc.so.6 failedattempt to open /usr/lib/x86_64-linux-gnu64/libc.so.6 failedattempt to open /usr/local/lib64/libc.so.6 failedattempt to open /lib64/libc.so.6 failedattempt to open /usr/lib64/libc.so.6 failedattempt to open /usr/local/lib/libc.so.6 failedattempt to open /lib/libc.so.6 failedattempt to open /usr/lib/libc.so.6 failedattempt to open /usr/x86_64-linux-gnu/lib64/libc.so.6 failedattempt to open /usr/x86_64-linux-gnu/lib/libc.so.6 failedattempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/mpi/fortran/mpif-h/.libs/libc.so.6 failedattempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/.libs/libc.so.6 failedattempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libc.so.6 failedattempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libc.so.6 failedattempt to open /usr/local/lib/libc.so.6 failedfound libc.so.6 at /usr/lib/x86_64-linux-gnu/libc.so.6libopen-pal.so.40 needed by /usr/lib/x86_64-linux-gnu/libmpi_mpifh.so.40attempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/.libs/libopen-pal.so.40 failedattempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/opal/.libs/libopen-pal.so.40 failedattempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libopen-pal.so.40 failedattempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libopen-pal.so.40 failedattempt to open /usr/local/lib/libopen-pal.so.40 failedfound libopen-pal.so.40 at /usr/lib/x86_64-linux-gnu/libopen-pal.so.40libopen-rte.so.40 needed by /usr/lib/x86_64-linux-gnu/libmpi.so.40attempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libopen-rte.so.40 failedattempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libopen-rte.so.40 failedattempt to open /usr/local/lib/libopen-rte.so.40 failedfound libopen-rte.so.40 at /usr/lib/x86_64-linux-gnu/libopen-rte.so.40libm.so.6 needed by /usr/lib/x86_64-linux-gnu/libmpi.so.40attempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libm.so.6 failedattempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libm.so.6 failedattempt to open /usr/local/lib/libm.so.6 failedfound libm.so.6 at /usr/lib/x86_64-linux-gnu/libm.so.6libhwloc.so.15 needed by /usr/lib/x86_64-linux-gnu/libmpi.so.40attempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libhwloc.so.15 failedattempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libhwloc.so.15 failedattempt to open /usr/local/lib/libhwloc.so.15 failedfound libhwloc.so.15 at /usr/lib/x86_64-linux-gnu/libhwloc.so.15ld-linux-x86-64.so.2 needed by /usr/lib/x86_64-linux-gnu/libc.so.6attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/ld-linux-x86-64.so.2 failedattempt to open /usr/local/lib/ld-linux-x86-64.so.2 failedfound ld-linux-x86-64.so.2 at /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2libevent_core-2.1.so.7 needed by /usr/lib/x86_64-linux-gnu/libopen-pal.so.40attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libevent_core-2.1.so.7 failedattempt to open /usr/local/lib/libevent_core-2.1.so.7 failedfound libevent_core-2.1.so.7 at /usr/lib/x86_64-linux-gnu/libevent_core-2.1.so.7libevent_pthreads-2.1.so.7 needed by /usr/lib/x86_64-linux-gnu/libopen-pal.so.40attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libevent_pthreads-2.1.so.7 failedattempt to open /usr/local/lib/libevent_pthreads-2.1.so.7 failedfound libevent_pthreads-2.1.so.7 at /usr/lib/x86_64-linux-gnu/libevent_pthreads-2.1.so.7libz.so.1 needed by /usr/lib/x86_64-linux-gnu/libopen-rte.so.40attempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libz.so.1 failedattempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libz.so.1 failedattempt to open /usr/local/lib/libz.so.1 failedfound libz.so.1 at /usr/lib/x86_64-linux-gnu/libz.so.1libudev.so.1 needed by /usr/lib/x86_64-linux-gnu/libhwloc.so.15attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libudev.so.1 failedattempt to open /usr/local/lib/libudev.so.1 failedfound libudev.so.1 at /usr/lib/x86_64-linux-gnu/libudev.so.1ld -lmpi_usempif08 --verbose | grep foundfound libmpi_mpifh.so.40 at /usr/lib/x86_64-linux-gnu/libmpi_mpifh.so.40found libmpi.so.40 at /usr/lib/x86_64-linux-gnu/libmpi.so.40ld: warning: cannot find entry symbol _start; not setting start addressfound libc.so.6 at /usr/lib/x86_64-linux-gnu/libc.so.6found libopen-pal.so.40 at /usr/lib/x86_64-linux-gnu/libopen-pal.so.40found libopen-rte.so.40 at /usr/lib/x86_64-linux-gnu/libopen-rte.so.40found libm.so.6 at /usr/lib/x86_64-linux-gnu/libm.so.6found libhwloc.so.15 at /usr/lib/x86_64-linux-gnu/libhwloc.so.15found ld-linux-x86-64.so.2 at /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2found libevent_core-2.1.so.7 at /usr/lib/x86_64-linux-gnu/libevent_core-2.1.so.7found libevent_pthreads-2.1.so.7 at /usr/lib/x86_64-linux-gnu/libevent_pthreads-2.1.so.7found libz.so.1 at /usr/lib/x86_64-linux-gnu/libz.so.1found libudev.so.1 at /usr/lib/x86_64-linux-gnu/libudev.so.1

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上面这段信息很长，有很多有价值的信息，如果你只想看关键部分，那么我保留其中的关键内容，来一个精华版的输出信息：

#ld -lmpi_usempif08 –verbose

GNU ld (GNU Binutils for Ubuntu) 2.38Supported emulations: elf_x86_64……using internal linker script: notice and this notice are preserved.*/OUTPUT_FORMAT("elf64-x86-64", "elf64-x86-64", "elf64-x86-64")OUTPUT_ARCH(i386:x86-64)ENTRY(_start)# 运行时可执行文件从代码段的 _start 位置开始运行。# 运行时需从哪些目录找动态库文件SEARCH_DIR("=/usr/local/lib/x86_64-linux-gnu"); SEARCH_DIR("=/lib/x86_64-linux-gnu"); SEARCH_DIR("=/usr/lib/x86_64-linux-gnu"); SEARCH_DIR("=/usr/lib/x86_64-linux-gnu64"); SEARCH_DIR("=/usr/local/lib64"); SEARCH_DIR("=/lib64"); SEARCH_DIR("=/usr/lib64"); SEARCH_DIR("=/usr/local/lib"); SEARCH_DIR("=/lib"); SEARCH_DIR("=/usr/lib"); SEARCH_DIR("=/usr/x86_64-linux-gnu/lib64"); SEARCH_DIR("=/usr/x86_64-linux-gnu/lib");# 二进制文件有哪些的代码段、数据段SECTIONS{PROVIDE (__executable_start = SEGMENT_START("text-segment", 0x400000)); . = SEGMENT_START("text-segment", 0x400000) + SIZEOF_HEADERS;.interp : { *(.interp) }…….rodata : { *(.rodata .rodata.* .gnu.linkonce.r.*) }……/* Thread Local Storage sections*/# 线程本地存储区域.tdata : { PROVIDE_HIDDEN (__tdata_start = .); *(.tdata .tdata.* .gnu.linkonce.td.*) }.tbss: { *(.tbss .tbss.* .gnu.linkonce.tb.*) *(.tcommon) }.preinit_array:{PROVIDE_HIDDEN (__preinit_array_start = .);KEEP (*(.preinit_array))PROVIDE_HIDDEN (__preinit_array_end = .);}# 数据区.data :{*(.data .data.* .gnu.linkonce.d.*)SORT(CONSTRUCTORS)}.data1: { *(.data1) }_edata = .; PROVIDE (edata = .);. = .;__bss_start = .;# BSS区.bss:{ ……} ……}# 下面是本文的重点关注部分==================================================# 文件1：逐个目录匹配是否找到被依赖的libmpi_usempif08.so 库文件ld: mode elf_x86_64attempt to open /usr/local/lib/x86_64-linux-gnu/libmpi_usempif08.so failedattempt to open /usr/local/lib/x86_64-linux-gnu/libmpi_usempif08.a failedattempt to open /lib/x86_64-linux-gnu/libmpi_usempif08.so succeeded# 找到了 libmpi_usempif08.so 库文件# 文件2：逐个目录匹配是否找到被依赖的 libmpi_mpifh.so 库文件libmpi_mpifh.so.40 needed by /lib/x86_64-linux-gnu/libmpi_usempif08.soattempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/mpi/fortran/mpif-h/.libs/libmpi_mpifh.so.40 failedattempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/.libs/libmpi_mpifh.so.40 failedattempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libmpi_mpifh.so.40 failedattempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libmpi_mpifh.so.40 failedattempt to open /usr/local/lib/libmpi_mpifh.so.40 failedfound libmpi_mpifh.so.40 at /usr/lib/x86_64-linux-gnu/libmpi_mpifh.so.40# 找到了 libmpi_mpifh.so 库文件# 找 libmpi.so.40 libmpi.so.40 needed by /lib/x86_64-linux-gnu/libmpi_usempif08.so……found libmpi.so.40 at /usr/lib/x86_64-linux-gnu/libmpi.so.40# 找 libc.so.6 libc.so.6 needed by /lib/x86_64-linux-gnu/libmpi_usempif08.so……found libc.so.6 at /usr/lib/x86_64-linux-gnu/libc.so.6# 找 libopen-pal.so.40libopen-pal.so.40 needed by /usr/lib/x86_64-linux-gnu/libmpi_mpifh.so.40……found libopen-pal.so.40 at /usr/lib/x86_64-linux-gnu/libopen-pal.so.40# 找 libopen-rte.so.40libopen-rte.so.40 needed by /usr/lib/x86_64-linux-gnu/libmpi.so.40……found libopen-rte.so.40 at /usr/lib/x86_64-linux-gnu/libopen-rte.so.40# 找 libm.so.6libm.so.6 needed by /usr/lib/x86_64-linux-gnu/libmpi.so.40……found libm.so.6 at /usr/lib/x86_64-linux-gnu/libm.so.6libhwloc.so.15 needed by /usr/lib/x86_64-linux-gnu/libmpi.so.40# 找 libhwloc.so.15……略# 找 libudev.so.1libudev.so.1 needed by /usr/lib/x86_64-linux-gnu/libhwloc.so.15attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libudev.so.1 failedattempt to open /usr/local/lib/libudev.so.1 failedfound libudev.so.1 at /usr/lib/x86_64-linux-gnu/libudev.so.1

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进一步，我们可以用 grep 过滤只显示 mpi_usempif08 实际找到的库的信息：

#ld -lmpi_usempif08 –verbose | grep found

found libmpi_mpifh.so.40 at /usr/lib/x86_64-linux-gnu/libmpi_mpifh.so.40found libmpi.so.40 at /usr/lib/x86_64-linux-gnu/libmpi.so.40ld: warning: cannot find entry symbol _start; not setting start addressfound libc.so.6 at /usr/lib/x86_64-linux-gnu/libc.so.6found libopen-pal.so.40 at /usr/lib/x86_64-linux-gnu/libopen-pal.so.40found libopen-rte.so.40 at /usr/lib/x86_64-linux-gnu/libopen-rte.so.40found libm.so.6 at /usr/lib/x86_64-linux-gnu/libm.so.6found libhwloc.so.15 at /usr/lib/x86_64-linux-gnu/libhwloc.so.15found ld-linux-x86-64.so.2 at /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2found libevent_core-2.1.so.7 at /usr/lib/x86_64-linux-gnu/libevent_core-2.1.so.7found libevent_pthreads-2.1.so.7 at /usr/lib/x86_64-linux-gnu/libevent_pthreads-2.1.so.7found libz.so.1 at /usr/lib/x86_64-linux-gnu/libz.so.1found libudev.so.1 at /usr/lib/x86_64-linux-gnu/libudev.so.1

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而ldd 与 ld是不同的。ldd是分析linux的运行库的依赖关系、ld是可执行文件链接器常用于C/C++/Fortran等语言代码生成可执行文件的链接阶段。

我们看下 使用 ldd 对同一个动态库所依赖的其他库的分析：

#ldd/usr/lib/x86_64-linux-gnu/libmpi_usempif08.so.40.30.0

 linux-vdso.so.1 (0x00007ffd2f3fd000) libmpi_mpifh.so.40 => /usr/lib/x86_64-linux-gnu/libmpi_mpifh.so.40 (0x00007f34366bf000) libmpi.so.40 => /usr/lib/x86_64-linux-gnu/libmpi.so.40 (0x00007f3436588000) libc.so.6 => /usr/lib/x86_64-linux-gnu/libc.so.6 (0x00007f3436200000) libopen-pal.so.40 => /usr/lib/x86_64-linux-gnu/libopen-pal.so.40 (0x00007f34364d5000) libopen-rte.so.40 => /usr/lib/x86_64-linux-gnu/libopen-rte.so.40 (0x00007f3436143000) libm.so.6 => /usr/lib/x86_64-linux-gnu/libm.so.6 (0x00007f343605c000) libhwloc.so.15 => /usr/lib/x86_64-linux-gnu/libhwloc.so.15 (0x00007f3436477000) /lib64/ld-linux-x86-64.so.2 (0x00007f343677c000) libevent_core-2.1.so.7 => /usr/lib/x86_64-linux-gnu/libevent_core-2.1.so.7 (0x00007f3436442000) libevent_pthreads-2.1.so.7 => /usr/lib/x86_64-linux-gnu/libevent_pthreads-2.1.so.7 (0x00007f343643d000) libz.so.1 => /usr/lib/x86_64-linux-gnu/libz.so.1 (0x00007f3436040000) libudev.so.1 => /usr/lib/x86_64-linux-gnu/libudev.so.1 (0x00007f3436016000)

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这里的顺序与ld -lmpi_usempif08 –verbose | grep found 的结果是一致的。

以上就是涨知识了，Linux的ld和ldd一起用，可以帮我们分析运行时加载库文件失败的原因的详细内容，更多请关注【创想鸟】其它相关文章！