Can't find vprintk_safe in System.map

[Chan Kim]

Hello all

 

I'm doing a experiment and found a strange phenomenon.

This is the vprintk_func( ) function defined in kernel/printk/printk_safe.c
(in linux 5.4.21, I'll update to recent version later, it's arm64).

 

__printf(1, 0) int vprintk_func(const char *fmt, va_list args)

{

    /*

     * Try to use the main logbuf even in NMI. But avoid calling console

     * drivers that might have their own locks.

     */

    if ((this_cpu_read(printk_context) & PRINTK_NMI_DIRECT_CONTEXT_MASK) &&

        raw_spin_trylock(&logbuf_lock)) {

        int len;

 

        len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);

        raw_spin_unlock(&logbuf_lock);

        defer_console_output();

        return len;

    }

 

    /* Use extra buffer in NMI when logbuf_lock is taken or in safe mode. */

    if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)

        return vprintk_nmi(fmt, args);

 

    /* Use extra buffer to prevent a recursion deadlock in safe mode. */

    if (this_cpu_read(printk_context) & PRINTK_SAFE_CONTEXT_MASK)

        return vprintk_safe(fmt, args);

 

    /* No obstacles. */

    return vprintk_default(fmt, args);

}

 

In qemu test, it passes all the printk_context check and enters
vprintk_default( ) funciton but in our FPGA board (with only 8MB ram instead
of DDR), 

by writing debug information to some variables, I found the program seems to
enter vprintk_safe( ) function and stuck somewhere inside.

But when I examine the System.map file, I cannot find the vprintk_safe
function and vprintk_nmi (I can find vprintk_default). I'm curious if this
may be related to the malfunction.

How can this happen? And how should I understand this?

Thank you!

 

Chan Kim

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20220208/5c1036b7/attachment.html>