使用Linux的ld和ldd组合可以帮助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

GNU ld (GNU Binutils for Ubuntu) 2.38
Supported emulations:
 elf_x86_64
 elf32_x86_64
 elf_i386
 elf_iamcu
 elf_l1om
 elf_k1om
 i386pep
 i386pe
using internal linker script:
==================================================
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PROVIDE_HIDDEN (__init_array_end = .);
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PROVIDE_HIDDEN (__fini_array_start = .);
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PROVIDE_HIDDEN (__fini_array_end = .);
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KEEP (*crtbegin?.o(.ctors))
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 The .ctor section from the crtend file contains the
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KEEP (*(SORT(.ctors.*)))
KEEP (*(.ctors))
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FIXME: Why do we need it? When there is no .bss section, we do not
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}


==================================================
ld: mode elf_x86_64
attempt to open /usr/local/lib/x86_64-linux-gnu/libmpi_usempif08.so failed
attempt to open /usr/local/lib/x86_64-linux-gnu/libmpi_usempif08.a failed
attempt to open /lib/x86_64-linux-gnu/libmpi_usempif08.so succeeded
/lib/x86_64-linux-gnu/libmpi_usempif08.so
libmpi_mpifh.so.40 needed by /lib/x86_64-linux-gnu/libmpi_usempif08.so
attempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/mpi/fortran/mpif-h/.libs/libmpi_mpifh.so.40 failed
attempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/.libs/libmpi_mpifh.so.40 failed
attempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libmpi_mpifh.so.40 failed
attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libmpi_mpifh.so.40 failed
attempt to open /usr/local/lib/libmpi_mpifh.so.40 failed
found libmpi_mpifh.so.40 at /usr/lib/x86_64-linux-gnu/libmpi_mpifh.so.40
libmpi.so.40 needed by /lib/x86_64-linux-gnu/libmpi_usempif08.so
attempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/mpi/fortran/mpif-h/.libs/libmpi.so.40 failed
attempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/.libs/libmpi.so.40 failed
attempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libmpi.so.40 failed
attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libmpi.so.40 failed
attempt to open /usr/local/lib/libmpi.so.40 failed
found libmpi.so.40 at /usr/lib/x86_64-linux-gnu/libmpi.so.40
libc.so.6 needed by /lib/x86_64-linux-gnu/libmpi_usempif08.so
attempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/mpi/fortran/mpif-h/.libs/libc.so.6 failed
attempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/.libs/libc.so.6 failed
attempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libc.so.6 failed
attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libc.so.6 failed
attempt to open /usr/local/lib/libc.so.6 failed
attempt to open /usr/lib/x86_64-linux-gnu/fortran/gfortran/libc.so.6 failed
attempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libc.so.6 failed
attempt to open /usr/local/lib/x86_64-linux-gnu/libc.so.6 failed
attempt to open /usr/local/lib/x86_64-linux-gnu/libc.so.6 failed
attempt to open /usr/lib/x86_64-linux-gnu64/libc.so.6 failed
attempt to open /usr/local/lib64/libc.so.6 failed
attempt to open /lib64/libc.so.6 failed
attempt to open /usr/lib64/libc.so.6 failed
attempt to open /usr/local/lib/libc.so.6 failed
attempt to open /lib/libc.so.6 failed
attempt to open /usr/lib/libc.so.6 failed
attempt to open /usr/x86_64-linux-gnu/lib64/libc.so.6 failed
attempt to open /usr/x86_64-linux-gnu/lib/libc.so.6 failed
attempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/mpi/fortran/mpif-h/.libs/libc.so.6 failed
attempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/.libs/libc.so.6 failed
attempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libc.so.6 failed
attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libc.so.6 failed
attempt to open /usr/local/lib/libc.so.6 failed
found libc.so.6 at /usr/lib/x86_64-linux-gnu/libc.so.6
libopen-pal.so.40 needed by /usr/lib/x86_64-linux-gnu/libmpi_mpifh.so.40
attempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/.libs/libopen-pal.so.40 failed
attempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/opal/.libs/libopen-pal.so.40 failed
attempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libopen-pal.so.40 failed
attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libopen-pal.so.40 failed
attempt to open /usr/local/lib/libopen-pal.so.40 failed
found libopen-pal.so.40 at /usr/lib/x86_64-linux-gnu/libopen-pal.so.40
libopen-rte.so.40 needed by /usr/lib/x86_64-linux-gnu/libmpi.so.40
attempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libopen-rte.so.40 failed
attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libopen-rte.so.40 failed
attempt to open /usr/local/lib/libopen-rte.so.40 failed
found libopen-rte.so.40 at /usr/lib/x86_64-linux-gnu/libopen-rte.so.40
libm.so.6 needed by /usr/lib/x86_64-linux-gnu/libmpi.so.40
attempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libm.so.6 failed
attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libm.so.6 failed
attempt to open /usr/local/lib/libm.so.6 failed
found libm.so.6 at /usr/lib/x86_64-linux-gnu/libm.so.6
libhwloc.so.15 needed by /usr/lib/x86_64-linux-gnu/libmpi.so.40
attempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libhwloc.so.15 failed
attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libhwloc.so.15 failed
attempt to open /usr/local/lib/libhwloc.so.15 failed
found libhwloc.so.15 at /usr/lib/x86_64-linux-gnu/libhwloc.so.15
ld-linux-x86-64.so.2 needed by /usr/lib/x86_64-linux-gnu/libc.so.6
attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/ld-linux-x86-64.so.2 failed
attempt to open /usr/local/lib/ld-linux-x86-64.so.2 failed
found ld-linux-x86-64.so.2 at /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2
libevent_core-2.1.so.7 needed by /usr/lib/x86_64-linux-gnu/libopen-pal.so.40
attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libevent_core-2.1.so.7 failed
attempt to open /usr/local/lib/libevent_core-2.1.so.7 failed
found libevent_core-2.1.so.7 at /usr/lib/x86_64-linux-gnu/libevent_core-2.1.so.7
libevent_pthreads-2.1.so.7 needed by /usr/lib/x86_64-linux-gnu/libopen-pal.so.40
attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libevent_pthreads-2.1.so.7 failed
attempt to open /usr/local/lib/libevent_pthreads-2.1.so.7 failed
found libevent_pthreads-2.1.so.7 at /usr/lib/x86_64-linux-gnu/libevent_pthreads-2.1.so.7
libz.so.1 needed by /usr/lib/x86_64-linux-gnu/libopen-rte.so.40
attempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libz.so.1 failed
attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libz.so.1 failed
attempt to open /usr/local/lib/libz.so.1 failed
found libz.so.1 at /usr/lib/x86_64-linux-gnu/libz.so.1
libudev.so.1 needed by /usr/lib/x86_64-linux-gnu/libhwloc.so.15
attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libudev.so.1 failed
attempt to open /usr/local/lib/libudev.so.1 failed
found libudev.so.1 at /usr/lib/x86_64-linux-gnu/libudev.so.1


ld -lmpi_usempif08 --verbose | grep found
found libmpi_mpifh.so.40 at /usr/lib/x86_64-linux-gnu/libmpi_mpifh.so.40
found libmpi.so.40 at /usr/lib/x86_64-linux-gnu/libmpi.so.40
ld: warning: cannot find entry symbol _start; not setting start address
found libc.so.6 at /usr/lib/x86_64-linux-gnu/libc.so.6
found libopen-pal.so.40 at /usr/lib/x86_64-linux-gnu/libopen-pal.so.40
found libopen-rte.so.40 at /usr/lib/x86_64-linux-gnu/libopen-rte.so.40
found libm.so.6 at /usr/lib/x86_64-linux-gnu/libm.so.6
found libhwloc.so.15 at /usr/lib/x86_64-linux-gnu/libhwloc.so.15
found ld-linux-x86-64.so.2 at /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2
found libevent_core-2.1.so.7 at /usr/lib/x86_64-linux-gnu/libevent_core-2.1.so.7
found libevent_pthreads-2.1.so.7 at /usr/lib/x86_64-linux-gnu/libevent_pthreads-2.1.so.7
found libz.so.1 at /usr/lib/x86_64-linux-gnu/libz.so.1
found libudev.so.1 at /usr/lib/x86_64-linux-gnu/libudev.so.1

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) 2.38
Supported 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_64
attempt to open /usr/local/lib/x86_64-linux-gnu/libmpi_usempif08.so failed
attempt to open /usr/local/lib/x86_64-linux-gnu/libmpi_usempif08.a failed
attempt 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.so
attempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/mpi/fortran/mpif-h/.libs/libmpi_mpifh.so.40 failed
attempt to open /build/openmpi-RCkqwI/openmpi-4.1.2/debian/build-gfortran/ompi/.libs/libmpi_mpifh.so.40 failed
attempt to open /usr/lib/x86_64-linux-gnu/openmpi/lib/libmpi_mpifh.so.40 failed
attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libmpi_mpifh.so.40 failed
attempt to open /usr/local/lib/libmpi_mpifh.so.40 failed
found 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.40
libopen-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.40
libopen-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.6
libm.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.6
libhwloc.so.15 needed by /usr/lib/x86_64-linux-gnu/libmpi.so.40

# 找 libhwloc.so.15
……略

# 找 libudev.so.1
libudev.so.1 needed by /usr/lib/x86_64-linux-gnu/libhwloc.so.15
attempt to open /usr/lib/x86_64-linux-gnu/libfakeroot/libudev.so.1 failed
attempt to open /usr/local/lib/libudev.so.1 failed
found libudev.so.1 at /usr/lib/x86_64-linux-gnu/libudev.so.1

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

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)

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