当 SOVERSION
的文档出现时,我正在考虑对一个小型个人项目的共享库进行版本控制。 target 属性提到在 OS X 和 iOS 等 Mach-O 系统上,对应的是“兼容版本”,而 VERSION
对应于“当前版本”。
在 Linux 上,它只是类似于 VERSION 5.4.2
和 SOVERSION 5
表示该库与 5.0 及更新版本兼容,以及 VERSION
以 <major>.<minor>
形式用作 DLL 镜像版本在 Windows 上(我不确定 SOVERSION
在 Windows 上有什么区别)。
但是,the docs for the referenced FRAMEWORK
target property 中的示例说明您可能如何拥有 VERSION 16.4.0
和 SOVERSION 1.0.0
在 Mach-O 平台上(我对构建框架不感兴趣,只是想知道国外的版本控制方案。)
版本控制在 Mach-O 世界中是如何工作的?如果我删除某些功能,我习惯于只是撞主要版本,这将是兼容性中断,那么版本 16.4.0 的库怎么可能与该库的 1.0.0 版本保持兼容? “兼容”是什么意思?
最佳答案
首先,为了解决这个问题,框架只是名为 Something.framework/Something
的动态库。而不是 libsomething.dylib
.不过文件格式完全相同,所以在这篇文章中,我将简单地将它们称为 dylib。
现在,让我们从 mach-o/loader.h
的摘录开始 header (Mach-O 文件格式的事实上的权威来源):
/*
* Dynamicly linked shared libraries are identified by two things. The
* pathname (the name of the library as found for execution), and the
* compatibility version number. The pathname must match and the compatibility
* number in the user of the library must be greater than or equal to the
* library being used. The time stamp is used to record the time a library was
* built and copied into user so it can be use to determined if the library used
* at runtime is exactly the same as used to built the program.
*/
struct dylib {
union lc_str name; /* library's path name */
uint32_t timestamp; /* library's build time stamp */
uint32_t current_version; /* library's current version number */
uint32_t compatibility_version; /* library's compatibility vers number*/
};
/*
* A dynamically linked shared library (filetype == MH_DYLIB in the mach header)
* contains a dylib_command (cmd == LC_ID_DYLIB) to identify the library.
* An object that uses a dynamically linked shared library also contains a
* dylib_command (cmd == LC_LOAD_DYLIB, LC_LOAD_WEAK_DYLIB, or
* LC_REEXPORT_DYLIB) for each library it uses.
*/
struct dylib_command {
uint32_t cmd; /* LC_ID_DYLIB, LC_LOAD_{,WEAK_}DYLIB,
LC_REEXPORT_DYLIB */
uint32_t cmdsize; /* includes pathname string */
struct dylib dylib; /* the library identification */
};
正如评论中所解释的,
struct dylib
嵌入在库中以及针对它的二进制链接中,两者都包含 current_version
的副本。和 compatibility_version
.后者的工作原理在那里有解释,但前者不是地址。相关文档可以在
dyld
上找到。手册页(来源是 here ,但在 man
之外不好看):DYLD_VERSIONED_FRAMEWORK_PATH
This is a colon separated list of directories that contain potential override frame-
works. The dynamic linker searches these directories for frameworks. For each
framework found dyld looks at its LC_ID_DYLIB and gets the current_version and
install name. Dyld then looks for the framework at the install name path. Whichever
has the larger current_version value will be used in the process whenever a framework
with that install name is required. This is similar to DYLD_FRAMEWORK_PATH except
instead of always overriding, it only overrides is the supplied framework is newer.
Note: dyld does not check the framework's Info.plist to find its version. Dyld only
checks the -current_version number supplied when the framework was created.
[...]
DYLD_VERSIONED_LIBRARY_PATH
This is a colon separated list of directories that contain potential override
libraries. The dynamic linker searches these directories for dynamic libraries. For
each library found dyld looks at its LC_ID_DYLIB and gets the current_version and
install name. Dyld then looks for the library at the install name path. Whichever
has the larger current_version value will be used in the process whenever a dylib
with that install name is required. This is similar to DYLD_LIBRARY_PATH except
instead of always overriding, it only overrides is the supplied library is newer.
简而言之:
compatibility_version
用于确定库对于想要加载它的二进制文件是否“足够新”。 current_version
用于在有多个可用库时选择一个库。 至于您对当前版本
16.4.0
的困惑兼容版本为 1.0.0
: 从看 some sources ,每当引入任何类型的功能时,Apple 似乎都会提升主要版本,并且使用次要版本几乎只修复错误,AFAIK。所以他们叫什么
16.4.0
,我可能会调用 1.16.4
. ;)
关于macos - Mach-O 平台上的库版本控制,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/51940963/