Makefile Special Built-in Target Names(Makefile内建特殊目标)

4.9 Special Built-in Target Names

http://www.gnu.org/software/make/manual/make.html

.PHONY    .SUFFIXES    .DEFAULT    .PRECIOUS    .INTERMEDIATE
.SECONDARY       .SECONDEXPANSION       .DELETE_ON_ERROR       .IGNORE       .LOW_RESOLUTION_TIME
.SILENT      .EXPORT_ALL_VARIABLES    .NOTPARALLEL    .ONESHELL       .POSIX

Certain names have special meanings if they appear as targets.

.PHONY

The prerequisites of the special target .PHONY are considered to be phony targets. When it is time to consider such a target, make will run its recipe unconditionally, regardless of whether a file with that name exists or what its last-modification time is. See Phony Targets.

目标“.PHONY”的所有的依赖被作为伪目标。伪目标时这样一个目标：当使用make命令行指定此目标时，这个目标所在规则定义的命令、无论目标文件是否存在都会被无条件执行。

.SUFFIXES

The prerequisites of the special target .SUFFIXES are the list of suffixes to be used in checking for suffix rules. See Old-Fashioned Suffix Rules.

特殊目标“SUFFIXES”的所有依赖指出了一系列在后缀规则中需要检查的后缀名（就是当前make需要处理的后缀）。

.DEFAULT

The recipe specified for .DEFAULT is used for any target for which no rules are found (either explicit rules or implicit rules). See Last Resort. If a .DEFAULT recipe is specified, every file mentioned as a prerequisite, but not as a target in a rule, will have that recipe executed on its behalf. See Implicit Rule Search Algorithm.

Makefile中，目标“.DEFAULT”所在规则定义的命令，被用在重建那些没有具体规则的目标（明确规则和隐含规则）。就是说一个文件作为某个规则的依赖，但却不是另外一个规则的目标时。Make程序无法找到重建此文件的规则，此种情况时就执行“.DEFAULT”所指定的命令。

.PRECIOUS

The targets which .PRECIOUS depends on are given the following special treatment: if make is killed or interrupted during the execution of their recipes, the target is not deleted. See Interrupting or Killing make. Also, if the target is an intermediate file, it will not be deleted after it is no longer needed, as is normally done. See Chains of Implicit Rules. In this latter respect it overlaps with the .SECONDARY special target.

You can also list the target pattern of an implicit rule (such as ‘%.o’) as a prerequisite file of the special target .PRECIOUS to preserve intermediate files created by rules whose target patterns match that file’s name.

目标“.PRECIOUS”的所有依赖文件在make过程中会被特殊处理：当命令在执行过程中被中断时，make不会删除它们（可参考5.5 中断make的执行一节）。而且如果目标的依赖文件是中间过程文件，同样这些文件不会被删除。这一点目标“.PRECIOUS”和目标“.SECONDAY”实现的功能相同。
另外，目标“.PRECIOUS”的依赖文件也可以是一个模式，例如“%.o”。这样可以保留有规则创建的中间过程文件。

.INTERMEDIATE

The targets which .INTERMEDIATE depends on are treated as intermediate files. See Chains of Implicit Rules. .INTERMEDIATE with no prerequisites has no effect.

目标“.INTERMEDIATE”的依赖文件在make时被作为中间过程文件对待。没有任何依赖文件的目标“.INTERMEDIATE”没有意义。

.SECONDARY

The targets which .SECONDARY depends on are treated as intermediate files, except that they are never automatically deleted. See Chains of Implicit Rules.

.SECONDARY with no prerequisites causes all targets to be treated as secondary (i.e., no target is removed because it is considered intermediate).

目标“.SECONDARY”的依赖文件被作为中间过程文件对待。但这些文件不会被自动删除。
没有任何依赖文件的目标“.SECONDARY”的含义是：将所有的文件作为中间过程文件（不会自动删除任何文件）。

.SECONDEXPANSION

If .SECONDEXPANSION is mentioned as a target anywhere in the makefile, then all prerequisite lists defined after it appears will be expanded a second time after all makefiles have been read in. See Secondary Expansion.

.DELETE_ON_ERROR

If .DELETE_ON_ERROR is mentioned as a target anywhere in the makefile, then make will delete the target of a rule if it has changed and its recipe exits with a nonzero exit status, just as it does when it receives a signal. See Errors in Recipes.

如果在Makefile中存在特殊目标“.DELETE_ON_ERROR”，make在执行过程中，如果规则的命令执行错误，将删除已经被修改的目标文件。

.IGNORE

If you specify prerequisites for .IGNORE, then make will ignore errors in execution of the recipe for those particular files. The recipe for .IGNORE (if any) is ignored.

If mentioned as a target with no prerequisites, .IGNORE says to ignore errors in execution of recipes for all files. This usage of ‘.IGNORE’ is supported only for historical compatibility. Since this affects every recipe in the makefile, it is not very useful; we recommend you use the more selective ways to ignore errors in specific recipes. See Errors in Recipes.

如果给目标“.IGNORE”指定依赖文件，则忽略创建这个文件所执行命令的错误。给此目标指定命令是没有意义的。当此目标没有依赖文件时，将忽略所有命令执行的错误。

.LOW_RESOLUTION_TIME

If you specify prerequisites for .LOW_RESOLUTION_TIME, make assumes that these files are created by commands that generate low resolution time stamps. The recipe for the .LOW_RESOLUTION_TIME target are ignored.

The high resolution file time stamps of many modern file systems lessen the chance of make incorrectly concluding that a file is up to date. Unfortunately, some hosts do not provide a way to set a high resolution file time stamp, so commands like ‘cp -p’ that explicitly set a file’s time stamp must discard its sub-second part. If a file is created by such a command, you should list it as a prerequisite of .LOW_RESOLUTION_TIME so that make does not mistakenly conclude that the file is out of date. For example:

.LOW_RESOLUTION_TIME: dst
dst: src
        cp -p src dst

Since ‘cp -p’ discards the sub-second part ofsrc’s time stamp,dstis typically slightly older thansrceven when it is up to date. The .LOW_RESOLUTION_TIME line causes make to considerdstto be up to date if its time stamp is at the start of the same second thatsrc’s time stamp is in.

Due to a limitation of the archive format, archive member time stamps are always low resolution. You need not list archive members as prerequisites of .LOW_RESOLUTION_TIME, as make does this automatically.

目标“.LOW_RESOLUTION_TIME”的依赖文件被make认为是低分辨率时间戳文件。给目标“.LOW_RESOLUTION_TIME”指定命令是没有意义的。
通常文件的时间辍都是高分辨率的，make在处理依赖关系时、对规则目标-依赖文件的高分辨率的时间戳进行比较，判断目标是否过期。但是在系统中并没有提供一个修改文件高分辨率时间辍的机制（方式），因此类似“cp -p”这样的命令在根据源文件创建目的文件时，所产生的目的文件的高分辨率时间辍的细粒度部分被丢弃（来源于源文件）。这样可能会造成目的文件的时间戳和源文件的相等甚至不及源文件新。处理此类命令创建的文件时，需要将命令创建的文件作为目标“.LOW_RESOLUTION_TIME”的依赖，声明这个文件是一个低分辨率时间辍的文件。例如：

.LOW_RESOLUTION_TIME: dst
dst: src
　　cp -p src dst
首先规则的命令“cp –p src dst”，所创建的文件“dst”在时间戳上稍稍比“src”晚（因为命令不能更新文件“dst”的细粒度时间）。因此make在判断文件依赖关系时会出现误判，将文件作为目标“.LOW_RESOLUTION_TIME”的依赖后，只要规则中目标和依赖文件的时间戳中的初始时间相等，就认为目标已经过期。这个特殊的目标主要作用是，弥补系统在没有提供修改文件高分辨率时间戳机制的情况下，某些命令在make中的一些缺陷。
对于静态库文件（文档文件）成员的更新也存在这个问题。make在创建或者更新静态库时，会自动将静态库的所有成员作为目标“.LOW_RESOLUTION_TIME”的依赖。

.SILENT

If you specify prerequisites for .SILENT, then make will not print the recipe used to remake those particular files before executing them. The recipe for .SILENT is ignored.

If mentioned as a target with no prerequisites, .SILENT says not to print any recipes before executing them. This usage of ‘.SILENT’ is supported only for historical compatibility. We recommend you use the more selective ways to silence specific recipes. See Recipe Echoing. If you want to silence all recipes for a particular run of make, use the ‘-s’ or ‘--silent’ option (see Options Summary).

出现在目标“.SILENT”的依赖列表中的文件，make在创建这些文件时，不打印出重建此文件所执行的命令。同样，给目标“.SILENT”指定命令行是没有意义的。
没有任何依赖文件的目标“.SILENT”告诉make在执行过程中不打印任何执行的命令。现行版本make支持目标“.SILENT”的这种功能和用法是为了和旧版本的兼容。在当前版本中如果需要禁命令执行过程的打印，可以使用make的命令行参数“-s”或者“--silent”。

.EXPORT_ALL_VARIABLES

Simply by being mentioned as a target, this tells make to export all variables to child processes by default. See Communicating Variables to a Sub-make.

此目标应该作为一个简单的没有依赖的目标，它的功能含义是将之后所有的变量传递给子make进程。

.NOTPARALLEL

If .NOTPARALLEL is mentioned as a target, then this invocation of make will be run serially, even if the ‘-j’ option is given. Any recursively invoked make command will still run recipes in parallel (unless its makefile also contains this target). Any prerequisites on this target are ignored.

Makefile中，如果出现目标“.NOPARALLEL”，则所有命令按照串行方式执行，即使存在make的命令行参数“-j”。但在递归调用的字make进程中，命令可以并行执行。此目标不应该有依赖文件，所有出现的依赖文件将被忽略。

所有定义的隐含规则后缀作为目标出现时，都被视为一个特殊目标，两个后缀串联起来也是如此，例如“.c.o”。这样的目标被称为后缀规则的目标，这种定义方式是已经过时的定义隐含规则的方法（目前，这种方式还被用在很多地方）。原则上，如果将其分为两个部分、并将它们加到后缀列表中，任何目标都可采用这种方式来表示。实际中，后缀通常以“.”开始，因此，以上的这些特别目标同样是以“.”开始。

.ONESHELL

If .ONESHELL is mentioned as a target, then when a target is built all lines of the recipe will be given to a single invocation of the shell rather than each line being invoked separately (see Recipe Execution).

.POSIX

If .POSIX is mentioned as a target, then the makefile will be parsed and run in POSIX-conforming mode. This does not mean that only POSIX-conforming makefiles will be accepted: all advanced GNU make features are still available. Rather, this target causes make to behave as required by POSIX in those areas where make’s default behavior differs.

In particular, if this target is mentioned then recipes will be invoked as if the shell had been passed the -e flag: the first failing command in a recipe will cause the recipe to fail immediately.

Any defined implicit rule suffix also counts as a special target if it appears as a target, and so does the concatenation of two suffixes, such as ‘.c.o’. These targets are suffix rules, an obsolete way of defining implicit rules (but a way still widely used). In principle, any target name could be special in this way if you break it in two and add both pieces to the suffix list. In practice, suffixes normally begin with ‘.’, so these special target names also begin with ‘.’. See Old-Fashioned Suffix Rules.