“静态链接"与“静态链接"之间有什么区别和“不是动态可执行文件"；从Linux LDD? [英] What's the difference between "statically linked" and "not a dynamic executable" from Linux ldd?

问题描述

考虑此AMD64汇编程序:

Consider this AMD64 assembly program:

.globl _start
_start:
    xorl %edi, %edi
    movl $60, %eax
    syscall

如果我用gcc -nostdlib进行编译并运行ldd a.out，我会得到:

If I compile that with gcc -nostdlib and run ldd a.out, I get this:

        statically linked

如果我改用gcc -static -nostdlib进行编译并运行ldd a.out，我会得到:

If I instead compile that with gcc -static -nostdlib and run ldd a.out, I get this:

        not a dynamic executable

statically linked和not a dynamic executable有什么区别?如果我的二进制文件已经静态链接，为什么添加-static会产生任何影响?

What's the difference between statically linked and not a dynamic executable? And if my binary was already statically linked, why does adding -static affect anything?

推荐答案

这里有两件事:

• 是否请求ELF解释器(ld.so).
  与#!/bin/sh类似，但对于二进制文件，应在_start之前运行.
  这是静态可执行文件与动态可执行文件之间的区别.
• 要加载的ld.so的动态链接库列表恰好为空.
  显然，这就是ldd所谓的静态链接"，即，您在构建时可能已链接的任何库都是静态库.

• Requesting an ELF interpreter (ld.so) or not.
  Like #!/bin/sh but for binaries, runs before your _start.
  This is the difference between a static vs. dynamic executable.
• The list of dynamically linked libraries for ld.so to load happens to be empty.
  This is apparently what ldd calls "statically linked", i.e. that any libraries you might have linked at build time were static libraries.

file和readelf之类的其他工具会提供更多信息，并使用与您期望的术语相匹配的术语.

Other tools like file and readelf give more information and use terminology that matches what you'd expect.

您的GCC已配置为是默认的，并且在没有动态库的特殊情况下，gcc不会创建静态饼.

Your GCC is configured so -pie is the default, and gcc doesn't make a static-pie for the special case of no dynamic libraries.

• gcc -nostdlib只是使一个PIE碰巧不链接到任何库，但在其他方面与普通的PIE相同，但指定了ELF解释器.
  ldd令人困惑地称其为静态链接".
  file:ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2 ...
• gcc -nostdlib -static覆盖-pie的默认值，并生成一个真正的静态可执行文件.
  file:ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked ...
• gcc -nostdlib -no-pie还选择创建静态可执行文件，以作为根本没有动态库的情况的优化.由于无论如何都无法对非PIE可执行文件进行ASLR处理，因此这是有道理的.逐字节与-static情况相同.

• gcc -nostdlib -static-pie 使ASLRable可执行文件不需要ELF解释器. GCC默认情况下不对gcc -pie -nostdlib执行此操作，这与无饼情况不同，在不涉及动态链接库的情况下，GCC选择避开ld.so.
  file:ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), statically linked ...

• gcc -nostdlib just makes a PIE that happens not to link to any libraries but is otherwise identical to a normal PIE, specifying an ELF interpreter.
  ldd confusingly calls this "statically linked".
  file : ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2 ...
• gcc -nostdlib -static overrides the -pie default and makes a true static executable.
  file : ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked ...
• gcc -nostdlib -no-pie also chooses to make a static executable as an optimization for the case where there are no dynamic libraries at all. Since a non-PIE executable couldn't have been ASLRed anyway, this makes sense. Byte-for-byte identical to the -static case.

• gcc -nostdlib -static-pie makes an ASLRable executable that doesn't need an ELF interpreter. GCC doesn't do this by default for gcc -pie -nostdlib, unlike the no-pie case where it chooses to sidestep ld.so when no dynamically-linked libraries are involved.
  file : ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), statically linked ...

-static-pie晦涩难懂，很少使用，而较早的file不会将其标识为静态链接.

-static-pie is obscure, rarely used, and older file doesn't identify it as statically linked.

-nostdlib并不表示-no-pie或-static，必须明确指定-static-pie才能实现.

-nostdlib doesn't imply -no-pie or -static, and -static-pie has to be explicitly specified to get that.

gcc -static-pie调用ld -static -pie，因此ld必须知道这意味着什么.与非PIE情况不同，在这种情况下，您不必显式地请求动态可执行文件，而如果您通过ld任何.so库，则只会得到一个.我认为这就是为什么您偶然从gcc -nostdlib -no-pie获取静态可执行文件的原因-GCC不必做任何特殊的事情，只需ld进行优化即可.

gcc -static-pie invokes ld -static -pie, so ld has to know what that means. Unlike with the non-PIE case where you don't have to ask for a dynamic executable explicitly, you just get one if you pass ld any .so libraries. I think that's why you happen to get a static executable from gcc -nostdlib -no-pie - GCC doesn't have to do anything special, it's just ld doing that optimization.

但是，即使没有共享库链接，当指定-pie时，ld也不会隐式启用-static.

But ld doesn't enable -static implicitly when -pie is specified, even when there are no shared libraries to link.

使用gcc --version gcc(Arch Linux 9.3.0-1)9.3.0
生成的示例 ld --version GNU ld(GNU Binutils)2.34(也readelf是binutils)
ldd --version ldd(GNU libc)2.31
file --version文件5.38-请注意，在最近的补丁程序中静态派检测已更改，Ubuntu挑选了未发布的补丁程序. (感谢@Joseph的侦探工作)-这在2019年检测到动态=拥有PT_INTERP来处理静态饼，但它已已还原以基于PT_DYNAMIC进行检测因此共享库算作dynamic. debian错误#948269 . static-pie是一个不起眼的很少使用的功能.

Examples generated with gcc --version gcc (Arch Linux 9.3.0-1) 9.3.0
ld --version GNU ld (GNU Binutils) 2.34 (also readelf is binutils)
ldd --version ldd (GNU libc) 2.31
file --version file-5.38 - note that static-pie detection has changed in recent patches, with Ubuntu cherry-picking an unreleased patch. (Thanks @Joseph for the detective work) - this in 2019 detected dynamic = having a PT_INTERP to handle static-pie, but it was reverted to detect based on PT_DYNAMIC so shared libraries count as dynamic. debian bug #948269. static-pie is an obscure rarely-used feature.

GCC最终运行ld -pie exit.o，并且指定了动态链接器路径，并且没有库. (还有很多其他选项来支持可能的LTO链接时间优化，但是这里的键是-dynamic-linker /lib64/ld-linux-x86-64.so.2 -pie.collect2只是ld的包装.)

GCC ends up running ld -pie exit.o with a dynamic linker path specified, and no libraries. (And a boatload of other options to support possible LTO link-time optimization, but the keys here are -dynamic-linker /lib64/ld-linux-x86-64.so.2 -pie. collect2 is just a wrapper around ld.)

$ gcc -nostdlib exit.s -v      # output manually line wrapped with \ for readability
...
COLLECT_GCC_OPTIONS='-nostdlib' '-v' '-mtune=generic' '-march=x86-64'
 /usr/lib/gcc/x86_64-pc-linux-gnu/9.3.0/collect2  \
-plugin /usr/lib/gcc/x86_64-pc-linux-gnu/9.3.0/liblto_plugin.so \
-plugin-opt=/usr/lib/gcc/x86_64-pc-linux-gnu/9.3.0/lto-wrapper \
-plugin-opt=-fresolution=/tmp/ccoNx1IR.res \
--build-id --eh-frame-hdr --hash-style=gnu \
-m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -pie \
-L/usr/lib/gcc/x86_64-pc-linux-gnu/9.3.0 \
-L/usr/lib/gcc/x86_64-pc-linux-gnu/9.3.0/../../../../lib -L/lib/../lib \
-L/usr/lib/../lib \
-L/usr/lib/gcc/x86_64-pc-linux-gnu/9.3.0/../../.. \
/tmp/cctm2fSS.o

您将获得一个动态PIE，而无需依赖其他库.运行它仍然会在其上调用"ELF解释程序" /lib64/ld-linux-x86-64.so.2，该ELF解释程序/lib64/ld-linux-x86-64.so.2在跳转到_start之前运行. (尽管内核已经将可执行文件的ELF段以及ld.so的text/data/bss映射到ASLRed虚拟地址).

You get a dynamic PIE with no dependencies on other libraries. Running it still invokes the "ELF interpreter" /lib64/ld-linux-x86-64.so.2 on it which runs before jumping to your _start. (Although the kernel has already mapped the executable's ELF segments to ASLRed virtual addresses, along with ld.so's text / data / bss).

file和readelf更具描述性.

file and readelf are more descriptive.

$ gcc -nostdlib exit.s -o exit-default
$ ls -l exit-default 
-rwxr-xr-x 1 peter peter 13536 May  2 02:15 exit-default 
$ ldd exit-default 
        statically linked
$ file exit-default
exit-default: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=05a4d1bdbc94d6f91cca1c9c26314e1aa227a3a5, not stripped

$ readelf -a exit-default
...
  Type:                              DYN (Shared object file)
  Machine:                           Advanced Micro Devices X86-64
  Version:                           0x1
  Entry point address:               0x1000
...
Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  PHDR           0x0000000000000040 0x0000000000000040 0x0000000000000040
                 0x00000000000001f8 0x00000000000001f8  R      0x8
  INTERP         0x0000000000000238 0x0000000000000238 0x0000000000000238
                 0x000000000000001c 0x000000000000001c  R      0x1
      [Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]
  LOAD           0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x00000000000002b1 0x00000000000002b1  R      0x1000
  LOAD           0x0000000000001000 0x0000000000001000 0x0000000000001000
                 0x0000000000000009 0x0000000000000009  R E    0x1000
  ...   (the Read+Exec segment to be mapped at virt addr 0x1000 is where your text section was linked.)

如果您发现它，也可以看到不同之处:

If you strace it you can also see the differences:

$ gcc -nostdlib exit.s -o exit-default
$ strace ./exit-default
execve("./exit-default", ["./exit-default"], 0x7ffe1f526040 /* 51 vars */) = 0
brk(NULL)                               = 0x5617eb1e4000
arch_prctl(0x3001 /* ARCH_??? */, 0x7ffcea703380) = -1 EINVAL (Invalid argument)
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f9ff5b3e000
arch_prctl(ARCH_SET_FS, 0x7f9ff5b3ea80) = 0
mprotect(0x5617eabac000, 4096, PROT_READ) = 0
exit(0)                                 = ?
+++ exited with 0 +++

vs. -static和-static-pie在用户空间中执行的第一条指令是您的_start(您也可以使用starti使用GDB进行检查).

vs. -static and -static-pie the first instruction executed in user-space is your _start (which you can also check with GDB using starti).

$ strace ./exit-static-pie 
execve("./exit-static-pie", ["./exit-static-pie"], 0x7ffcdac96dd0 /* 51 vars */) = 0
exit(0)                                 = ?
+++ exited with 0 +++

---

gcc -nostdlib -static-pie

---

gcc -nostdlib -static-pie

$ gcc -nostdlib -static-pie exit.s -o exit-static-pie
$ ls -l exit-static-pie
-rwxr-xr-x 1 peter peter 13440 May  2 02:18 exit-static-pie
peter@volta:/tmp$ ldd exit-static-pie
        statically linked
peter@volta:/tmp$ file exit-static-pie
exit-static-pie: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), statically linked, BuildID[sha1]=daeb4a8f11bec1bb1aaa13cd48d24b5795af638e, not stripped

$ readelf -a exit-static-pie 
...
  Type:                              DYN (Shared object file)
  Machine:                           Advanced Micro Devices X86-64
  Version:                           0x1
  Entry point address:               0x1000
...

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000229 0x0000000000000229  R      0x1000
  LOAD           0x0000000000001000 0x0000000000001000 0x0000000000001000
                 0x0000000000000009 0x0000000000000009  R E    0x1000
  ... (no Interp header, but still a read+exec text segment)

请注意，地址仍然是相对于映像库的，从而将ASLR保留给内核.

Notice that the addresses are still relative to the image base, leaving ASLR up to the kernel.

令人惊讶的是，ldd并没有说它不是动态可执行文件.这可能是一个错误，或者是某些实现细节的副作用.

Surprisingly, ldd doesn't say that it's not a dynamic executable. That might be a bug, or a side effect of some implementation detail.

$ gcc -nostdlib -static exit.s -o exit-static
$ ls -l exit-static
-rwxr-xr-x 1 peter peter 4744 May  2 02:26 exit-static
peter@volta:/tmp$ ldd exit-static
        not a dynamic executable
peter@volta:/tmp$ file exit-static
exit-static: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked, BuildID[sha1]=1b03e3d05709b7288fe3006b4696fd0c11fb1cb2, not stripped
peter@volta:/tmp$ readelf -a exit-static
ELF Header:
...
  Type:                              EXEC (Executable file)
  Machine:                           Advanced Micro Devices X86-64
  Version:                           0x1
  Entry point address:               0x401000
...   (Note the absolute entry-point address nailed down at link time)
      (And that the ELF type is EXEC, not DYN)

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000000000 0x0000000000400000 0x0000000000400000
                 0x000000000000010c 0x000000000000010c  R      0x1000
  LOAD           0x0000000000001000 0x0000000000401000 0x0000000000401000
                 0x0000000000000009 0x0000000000000009  R E    0x1000
  NOTE           0x00000000000000e8 0x00000000004000e8 0x00000000004000e8
                 0x0000000000000024 0x0000000000000024  R      0x4

 Section to Segment mapping:
  Segment Sections...
   00     .note.gnu.build-id 
   01     .text 
   02     .note.gnu.build-id 
   ...

这些都是程序头文件；与pie/static-pie不同，我没有遗漏任何东西，只是readelf -a输出的其他整个部分.

Those are all the program headers; unlike pie / static-pie I'm not leaving any out, just other whole parts of the readelf -a output.

还要注意程序头中的绝对虚拟地址，这些绝对虚拟地址不会使内核选择在虚拟地址空间中映射文件的位置.这是ELF对象的EXEC和DYN类型之间的区别. PIE可执行文件是带有入口点的共享对象，这使我们可以获取主要可执行文件的ASLR.实际的EXEC可执行文件具有链接时选择的内存布局.

Also note the absolute virtual addresses in the program headers that don't give the kernel a choice where in virtual address space to map the file. This is the difference between EXEC and DYN types of ELF objects. PIE executables are shared objects with an entry point, allowing us to get ASLR for the main executable. Actual EXEC executables have a link-time-chosen memory layout.

ldd显然仅在以下两种情况下报告不是动态可执行文件":

ldd apparently only reports "not a dynamic executable" when both:

• 没有ELF解释器(动态链接器)路径
• ELF类型= EXEC

这篇关于“静态链接"与“静态链接"之间有什么区别和“不是动态可执行文件"；从Linux LDD?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！