即使在声明中使用 :=，Makefile 变量替换显然也没有完成

发布于 2024-12-25 08:28:12 字数 1335 浏览 1 评论 0原文

我有一个主内核模块，其他内核模块可以与它进行通信。我已经像这样构建了模块（概念上）：

main module/
           |
            \drivers/
                    |
                    |\driver1
                    |\driver2
                     \driver3

由于这些是内核模块，我需要像这样编译它们：

make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) modules

但是，由于可以从以前的目录调用驱动程序的 Makefile，所以我需要执行 $(shell pwd) 在调用其他 make（linux 的 make）之前。所以 Makefile 现在看起来像这样：

CURRENT_DIR := $(shell pwd)

.PHONY: all
all:
    $(MAKE) -C /lib/modules/$(shell uname -r)/build M=$(CURRENT_DIR) modules

到目前为止，一切都很好并且工作完美。问题是这样的：我有一个驱动程序需要包含的文件，所以我必须给出要生成的包含路径。我第一次尝试

EXTRA_CFLAGS += -I../..

并立即理解为什么它不起作用（相对路径是 /lib/module/... 而不是当前目录）。所以我把它改成了：

MAIN_MODULE_HOME := $(CURRENT_DIR)/../..
EXTRA_CFLAGS += -I$(MAIN_MODULE_HOME)

奇怪的是，这不起作用！如果我手动编写

EXTRA_CFLAGS += -Ipath/I/get/from/pwd/../..

，它会编译！有人可以解释我做错了什么吗？在调用 make 之前，我 echoed $(CURRENT_DIR) 和 $(MAIN_MODULE_HOME) 并且这些变量是有意义的。

我知道 EXTRA_CFLAGS 不会立即评估，但由于 CURRENT_DIR 和 MAIN_MODULE_HOME 是用 := 声明的，我不知道不明白事情是如何变得一团糟的。

（如果有人能更好地表达问题标题，请这样做！）

原文

I have a main kernel module with which other kernel modules communicate. I have structured the modules like this (conceptually):

main module/
           |
            \drivers/
                    |
                    |\driver1
                    |\driver2
                     \driver3

Since these are kernel modules, I need to compile them like this:

make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) modules

However, since the Makefile of drivers can be called from previous directories, I need to do the $(shell pwd) before calling the other make (linux's make). So the Makefile now looks like this:

CURRENT_DIR := $(shell pwd)

.PHONY: all
all:
    $(MAKE) -C /lib/modules/$(shell uname -r)/build M=$(CURRENT_DIR) modules

So far it is fine and it works perfectly. The problem is this: I have a file that the drivers need to include, so I have to give the include path to make. I first tried

EXTRA_CFLAGS += -I../..

and immediately understood why it doesn't work (relative path would be to /lib/module/... not to current directory). So I changed it to:

MAIN_MODULE_HOME := $(CURRENT_DIR)/../..
EXTRA_CFLAGS += -I$(MAIN_MODULE_HOME)

Oddly enough, this doesn't work! If I write

EXTRA_CFLAGS += -Ipath/I/get/from/pwd/../..

manually, it compiles! Can someone explain what I am doing wrong? Before calling make, I echoed $(CURRENT_DIR) and $(MAIN_MODULE_HOME) and the variables are meaningful.

I know that EXTRA_CFLAGS is not immediately evaluated, but since CURRENT_DIR and MAIN_MODULE_HOME are declared with := I don't understand how things are getting messed up.

(If anyone can phrase the question title better, please do!)

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月亮坠入山谷 2025-01-01 08:28:12

您应该像这样传递 EXTRA_CFLAGS 来 make：

$(MAKE) -C /lib/modules/$(shell uname -r)/build M=$(CURRENT_DIR) \
           EXTRA_CFLAGS="$(EXTRA_CFLAGS)" modules

更新：

driver1/Makefile 的内容被读取两次：第一次 - 当您在 driver1 目录中运行 make 时，第二次 - 由 Kbuild 系统读取。

首先，CURRENT_DIR := $(shell pwd) 被评估为类似 /home/users/.../main module/drivers/driver1 的内容。其次，Kbuild 将 CURRENT_DIR := $(shell pwd) 评估为类似 /usr/src/linux-headers-2.6.32-33-generic/

中描述的情况LDD3、ch2、p24

技巧是按如下方式编写 makefile：

# If KERNELRELEASE is defined, we've been invoked from the
# kernel build system and can use its language.
ifneq ($(KERNELRELEASE),)
    obj-m := hello.o
# Otherwise we were called directly from the command
# line; invoke the kernel build system.
else
    KERNELDIR ?= /lib/modules/$(shell uname -r)/build
    PWD  := $(shell pwd)
default:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules
#endif

You should pass EXTRA_CFLAGS to make like this:

$(MAKE) -C /lib/modules/$(shell uname -r)/build M=$(CURRENT_DIR) \
           EXTRA_CFLAGS="$(EXTRA_CFLAGS)" modules

Update:

The content of driver1/Makefile is read twice: first - when you run make inside driver1 directory, second - by Kbuild system.

First, CURRENT_DIR := $(shell pwd) is evaluated to something like /home/users/.../main module/drivers/driver1. Second, Kbuild evaluates CURRENT_DIR := $(shell pwd) to something like /usr/src/linux-headers-2.6.32-33-generic/

That situation described in LDD3, ch2, p24

The trick is to write your makefile as follows:

# If KERNELRELEASE is defined, we've been invoked from the
# kernel build system and can use its language.
ifneq ($(KERNELRELEASE),)
    obj-m := hello.o
# Otherwise we were called directly from the command
# line; invoke the kernel build system.
else
    KERNELDIR ?= /lib/modules/$(shell uname -r)/build
    PWD  := $(shell pwd)
default:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules
#endif

回复收藏 0 原文

美男兮 2025-01-01 08:28:12

这很可能是因为 EXTRA_CFLAGS 的递归风格，它实际上是在子 make 中扩展的，而子 make 无法访问从中引用的 MAIN_MODULE_HOME 。

首先，尝试导出 MAIN_MODULE_HOME：

export MAIN_MODULE_HOME

在使用它之前，我还尝试展平 EXTRA_CFLAGS（但是，我不确定这是否是一个Kbuild 的良好实践）：

EXTRA_CFLAGS := $(EXTRA_CFLAGS)

It most likely because of recursive flavor of EXTRA_CFLAGS, which gets actually expanded in a sub-make, which doesn't have an access to MAIN_MODULE_HOME referred from it.

First, try to export MAIN_MODULE_HOME: