如何根据构建选项创建 makefile
很久以前，我记得使用过一些 Solaris make，它们有一个巧妙的选项，可以自动检测编译器选项何时更改，并适当地重建所有规则。例如，假设我从：
g++ -O3
切换到
g++ -g
那么所有文件都应该重新编译。我正在使用 gnu make，但还没有找到任何这样的功能，并且想知道是否有人有办法让它工作。
A long time ago, I remember using some Solaris make, and they had an ingenious option that would automatically detect when the compiler options had changed, and rebuild all rules appropriately. For example, suppose I switch from:
g++ -O3
to
g++ -g
Then all files should be recompiled. I'm using gnu make, and haven't found any feature like this, and was wondering whether anyone has a way of making it work.
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使用
gmake实现此目的的一个简单方法是将gcc选项写入文件中。然后，在Makefile中，将这些选项读取到一个变量中，在gcc命令行中使用这个变量，并将所有目标文件的依赖添加到这个选项文件中（可以在模式规则中完成）。A simple way to achieve this with
gmakeis to write thegccoptions into a file. Then, in theMakefile, read these options to a variable, use this variable in thegcccommand line, plus add the dependency for all object files to this option file (can be done in the pattern rule).这是执行此操作的基本方法（尽管我确信这是一个可怕的想法，请参见下文）：
发生的情况如下：在完成任何编译之前，当前的
CFLAGS是写出到CFLAGS.save。如果CFLAGS不等于CFLAGS_SAVE，则用户一定已更改它们。如果是这样，我们声明CFLAGS.save是假的，因此make将重建它。另请注意，如果CFLAGS已更改，我们将更新它，但内存中仍保留旧值。因此，我们必须为每个源文件递归调用make。对于一个大项目来说并不酷。另一个问题是，如果您忽略在命令行上指定 CFLAGS，它将返回并使用默认值重建所有内容。您可以通过测试
CFLAGS的$(origin)来解决这个问题，但说实话，不行。我的职业道德不允许我这么做。make的目的是简单。发行商已经很难理解打包者对构建工具的滥用（遗憾的是，大多数针对 automake 的指责都是由于这一点）。请对 Cthulloid 构建系统说不。此外，
make clean all CFLAGS='-Whatever -foo'也同样有效。Here's a basic way to do this (although I'm convinced it's a terrible idea, see below):
Here's what happens: Before any compilation is done, the current
CFLAGSare written out toCFLAGS.save. IfCFLAGSisn't equal toCFLAGS_SAVE, then the user must've changed them. If so, we declareCFLAGS.saveto be phony somakewill rebuild it. Note also that ifCFLAGShas changed, we'll update it but we'll still have the old value in memory. Therefore, we have to recursively invokemakefor every source file. Not cool on a big project.The other problem is that if you neglect to specify
CFLAGSon the command line, it will go back and rebuild everything with the default. You could work around this by testing the$(origin)ofCFLAGS, but seriously, no. My professional ethics won't allow me to stand for this.makeis meant to be simple. Distributors already have enough trouble understanding packagers' abuses of build tools (sadly, most of the blame levelled atautomakeis due to this). Please, just say no to Cthulhoid build systems.Besides,
make clean all CFLAGS='-Whatever -foo'will work just as well.只需让你的目标依赖于 makefile 本身：
Just make your target depend on the makefile itself: