Re: [Xenomai-help] unable to load nucleus module: unknown symbol

[Philippe Gerum <rpm@xenomai.org>]

On Thu, 2009-10-29 at 22:10 -0500, Jeff Weber wrote:
> I've built the xeno_nucleus as a module.  Neither depmod, nor modprobe
> can resolve the symbol "find_task_by_pid_ns":
> 
> depmod:
> WARNING:
> /lib/modules/2.6.31.5-xenomai-2.4.10/kernel/kernel/xenomai/nucleus/xeno_nucleus.ko
> needs unknown symbol find_task_by_pid_ns
> 
> modprobe [dmesg]:
> [  426.728630] xeno_nucleus: Unknown symbol find_task_by_pid_ns
> 
> Curiously, this symbol is in both my build System.map, and the kernel
> 
> bash # grep find_task_by_pid_ns System.map
> c102ecf6 T find_task_by_pid_ns
> 
> bash # cat /proc/kallsyms | grep find_task_by_pid_ns
> c102ecf6 T find_task_by_pid_ns
> 
> so this symbol should be publicly available.  I also noticed there is no
> EXPORT_SYMBOL() for find_task_by_pid_ns in the kernel code.
> 
> Any ideas what's keeping my xeno_nucleus.ko module from loading?
> 
> My config:
> linux-2.6.31.5 (current stable)
> xenomai-2.4.10
> adeos-ipipe-2.6.31.1-x86-2.4-06.patch

Please note that 2.6.31 is not officially supported by 2.4.x; at least,
not for all architectures. 2.5.x supports 2.6.31 and beyond.

Aside of this, the missing symbol is no more exported by 2.6.31 albeit
it used to be in 2.6.30. I guess that most people compile the nucleus
statically inside the kernel, so this has not been noticed before.

diff --git a/include/asm-generic/wrappers.h b/include/asm-generic/wrappers.h
index 18af70b..62f1d6e 100644
--- a/include/asm-generic/wrappers.h
+++ b/include/asm-generic/wrappers.h
@@ -480,8 +480,16 @@ unsigned long find_next_bit(const unsigned long *addr,
 #include <linux/semaphore.h>
 #include <linux/pid.h>
 
-#define find_task_by_pid(nr)		\
-  find_task_by_pid_ns(nr, &init_pid_ns)
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,31)
+static inline struct task_struct *wrap_find_task_by_pid(pid_t nr)
+{
+	return pid_task(find_pid_ns(nr, &init_pid_ns), PIDTYPE_PID);
+}
+#else /* LINUX_VERSION_CODE < 2.6.31 */
+#define wrap_find_task_by_pid(nr)	\
+	find_task_by_pid_ns(nr, &init_pid_ns)
+#endif /* LINUX_VERSION_CODE < 2.6.31 */
+
 #define kill_proc(pid, sig, priv)	\
   kill_proc_info(sig, (priv) ? SEND_SIG_PRIV : SEND_SIG_NOINFO, pid)
 
diff --git a/ksrc/nucleus/shadow.c b/ksrc/nucleus/shadow.c
index d6d1203..1eae0a1 100644
--- a/ksrc/nucleus/shadow.c
+++ b/ksrc/nucleus/shadow.c
@@ -1687,7 +1687,7 @@ void xnshadow_signal_completion(xncompletion_t __user *u_completion, int err)
 
 	read_lock(&tasklist_lock);
 
-	p = find_task_by_pid(completion.pid);
+	p = wrap_find_task_by_pid(completion.pid);
 
 	if (p)
 		wake_up_process(p);

> 
> thanks,
> Jeff
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-- 
Philippe.