implicit declaration 怎么造成的

最近在改进SD卡的SEP4020驱动时，在改掉所有的warning时老报一个implicit declaration of function 的警告错误，上网查了下原因，原来有两种情况会产生这种情况

1 没有把函数所在的c文件生成.o目标文件

2 在函数所在的c文件中定义了，但是没有在与之相关联的.h文件中声明

[root@mail linux]# make

CHK include/linux/version.h

make[1]: “include/asm-arm/mach-types.h”是最新的。

CHK include/linux/compile.h

CHK usr/initramfs_list

CC drivers/mmc/sep_mci.o

drivers/mmc/sep_mci.c: In function `sep4020sdi_probe':

drivers/mmc/sep_mci.c:745: warning: implicit declaration of function `clk_get'

drivers/mmc/sep_mci.c:745: warning: assignment makes pointer from integer without a cast

drivers/mmc/sep_mci.c:754: warning: implicit declaration of function `clk_enable'

drivers/mmc/sep_mci.c:800: warning: implicit declaration of function `clk_put'

drivers/mmc/sep_mci.c: In function `sep4020sdi_remove':

drivers/mmc/sep_mci.c:830: warning: implicit declaration of function `clk_disable'

drivers/mmc/sep_mci.c: In function `sep4020sdi_irq':

drivers/mmc/sep_mci.c:197: warning: 'sdi_cclear' might be used uninitialized in this function

drivers/mmc/sep_mci.c: In function `sep4020sdi_probe':

drivers/mmc/sep_mci.c:673: warning: 'host' might be used uninitialized in this function

drivers/mmc/sep_mci.c: At top level:

drivers/mmc/sep_mci.c:337: warning: 'sep4020sdi_irq_cd' defined but not used

LD drivers/mmc/built-in.o

LD drivers/built-in.o

GEN .version

CHK include/linux/compile.h

UPD include/linux/compile.h

CC init/version.o

LD init/built-in.o

LD .tmp_vmlinux1

KSYM.tmp_kallsyms1.S

AS .tmp_kallsyms1.o

LD .tmp_vmlinux2

KSYM.tmp_kallsyms2.S

AS .tmp_kallsyms2.o

LD vmlinux

SYSMAP System.map

SYSMAP .tmp_System.map

OBJCOPY arch/arm/boot/Image

Kernel: arch/arm/boot/Image is ready

GZIParch/arm/boot/compressed/piggy.gz

AS arch/arm/boot/compressed/piggy.o

LD arch/arm/boot/compressed/vmlinux

OBJCOPY arch/arm/boot/zImage

Kernel: arch/arm/boot/zImage is ready

Building modules, stage 2.

MODPOST

于是我在sep_mci.c的头部将 <linux/clk.h>包含进去就行了

这样就没有任何warning产生了，呵呵

piggy bank

n.

扑满

piggy bank

n.（名词）

A child's coin bank shaped like a pig.

猪形储蓄罐，猪形扑满：形状象猪的儿童硬币罐

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