feel free to correct me.
since SYSCALL_DEFINE2() is ultimately defined as (include/linux/syscalls.h):
#define SYSCALL_DEFINEx(x, name, ...) \
asmlinkage long sys##name(__SC_DECL##x(__VA_ARGS__)); \
static inline long SYSC##name(__SC_DECL##x(__VA_ARGS__)); \
asmlinkage long SyS##name(__SC_LONG##x(__VA_ARGS__)) \
{ \
__SC_TEST##x(__VA_ARGS__); \
return (long) SYSC##name(__SC_CAST##x(__VA_ARGS__)); \
} \
SYSCALL_ALIAS(sys##name, SyS##name); \
static inline long SYSC##name(__SC_DECL##x(__VA_ARGS__))
so your sys_clock_gettime() will ultimately be declared as asmlinkage
long sys_clock_gettime(), where asmlinkage will be mapped to something
(irrelevant here) not related to static, which means that the symbol
can always be accessed globally - just by issuing extern from the
demand side. Correct?
the error "symbol not found" must have occurred before this header
file is included. perhaps after u included this header, then extern,
then the symbol become accessible? I attempted, results as follows.
C-wise, syntactically / semantically correct - compilation no errors:
make -C /lib/modules/2.6.29-rc5/build
M=/sda1/download/linux-2.6/for-linus/drivers/mymodule modules
make[1]: Entering directory `/sda1/download/linux-2.6/for-linus'
CC [M] /sda1/download/linux-2.6/for-linus/drivers/mymodule/peter.o
/sda1/download/linux-2.6/for-linus/drivers/mymodule/peter.c: In
function ‘init_hello_4’:
/sda1/download/linux-2.6/for-linus/drivers/mymodule/peter.c:20:
warning: ‘which_clock’ is used uninitialized in this function
/sda1/download/linux-2.6/for-linus/drivers/mymodule/peter.c:20:
warning: ‘tp’ is used uninitialized in this function
Building modules, stage 2.
MODPOST 1 modules
WARNING: "sys_clock_gettime"
[/sda1/download/linux-2.6/for-linus/drivers/mymodule/peter.ko]
undefined!
CC /sda1/download/linux-2.6/for-linus/drivers/mymodule/peter.mod.o
LD [M] /sda1/download/linux-2.6/for-linus/drivers/mymodule/peter.ko
make[1]: Leaving directory `/sda1/download/linux-2.6/for-linus'
But during modposting stage, I suspect a CRC check is done, on top of
just the "extern" call, but because sys_clock_gettime() is not
declared as EXPORT_SYMBOL().....the symbol become not accessible from
a module. but if u compile the codes together with the kernel ELF
image, compilation and runtime should not have any error. Problem
now is modposting check done for a module......correct?
On Wed, Feb 25, 2009 at 6:08 PM, Ole Loots <ole@xxxxxxxxxxxxx> wrote:
> Hello,
>
> I want to call the kernel function sys_clock_gettime, but when I just try to
> call it, the linker complains about the unknown symbol/function
> sys_clock_gettime, so i have hard coded a function pointer in my module...:
>
> long (*p_sys_clock_gettime)(clockid_t, struct timespec *tp) = 0xc004373c;
>
> That works fine for my system, but I know thats not the way to do it. How is
> it done properly?
>
> Regards,
> Ole
>
>
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--
Regards,
Peter Teoh
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