A simple question: How to use EXPORT_SYMBOL()

hi，
I have a question in using linuxcnc 2.9.
I want to call the function defined in the other module. In module A, I export a function using EXPROT_SYMBOL(). In module B, I use "extern" to declare the function and call it. However, it always tells me "undefined symbol". How to solve this problem?

Presumably this is in C?

You may need ti #include A.h in B.c

hi, thanks!
yes, it's C. I did include A.h in B.c, but it doesn't work.

Maybe both modules also need to include <linux/module.h> ?

lkw.readthedocs.io/en/latest/doc/04_exporting_symbols.html

hi，thanks！
It doesn't work too. However, I find something in rtapi.h file.
I think it is not like the linux kernel modules.

#if !defined(__KERNEL__)
#define MODULE_INFO1(t, a, c) __attribute__((section(".modinfo"))) \
    t rtapi_info_##a = c; EXPORT_SYMBOL(rtapi_info_##a);
#define MODULE_INFO2x(t, a, b, c) MODULE_INFO2(t,a,b,c)
#define MODULE_INFO2(t, a, b, c) __attribute__((section(".modinfo"))) \
    t rtapi_info_##a##_##b = c; EXPORT_SYMBOL(rtapi_info_##a##_##b);
#define MODULE_PARM(v,t) MODULE_INFO2(const char*, type, v, t) MODULE_INFO2(void*, address, v, &v)
#define MODULE_PARM_DESC(v,t) MODULE_INFO2(const char*, description, v, t)
#define MODULE_LICENSE(s) MODULE_INFO1(const char*, license, s)
#define MODULE_AUTHOR(s) MODULE_INFO1(const char*, author, s)
#define MODULE_DESCRIPTION(s) MODULE_INFO1(const char*, description, s)
#define MODULE_SUPPORTED_DEVICE(s) MODULE_INFO1(const char*, supported_device, s)
#define MODULE_DEVICE_TABLE(x,y) MODULE_INFO2(struct rtapi_pci_device_id*, device_table, x, y)
#define MODULE_INFO(x,y) MODULE_INFO2x(char*, x, __LINE__, y)
#define EXPORT_SYMBOL(x) __attribute__((section(".rtapi_export"))) \
    char rtapi_exported_##x = #x;
#define EXPORT_SYMBOL_GPL(x) __attribute__((section(".rtapi_export"))) \
    char rtapi_exported_##x = #x;



 

Are you #including rtapi.h ?

Thinking about it, you can probably use the buuilt-in EXPORT_SYMBOL in kernel modules (ie, if using RTAI). But in uspace this may be re-defined to be something else. (as suggested by the code you posted)

yes, I include rtapi.h file.