kernel symbol marked with "T" in /proc/kallsyms is not exported
Solution 1:
Mark "T" in /proc/kallsyms
means that symbol is globally visible, and can be used in other kernel's code (e.g. by drivers, compiled built-in).
But for being usable in kernel module's code, symbol is needed to be exported using EXPORT_SYMBOL
or similar. List of exported symbols is maintained separately from list of all symbols in the kernel.
Exported symbols can be found in file /lib/modules/<kernel-version>/build/Module.symvers
.
(this file should exist for possibility to build kernel modules against given kernel).
Solution 2:
To use kernel symbols that are global, but not exported (such as the machine_power_off
symbol that you mention), you can use kallsyms_lookup
in your module code:
#include <linux/kallsyms.h>
static void (*machine_power_off_p)(void);
machine_power_off_p = (void*) kallsyms_lookup_name("machine_power_off");
Now you can call the machine_power_off
function via the machine_power_off_p
pointer:
(*machine_power_off_p)();