On Fri, 25 Apr 2008, Mulyadi Santosa wrote:
> Hi..
>
> On Fri, Apr 25, 2008 at 12:44 PM, Robert P. J. Day
> <rpjday@xxxxxxxxxxxxxx> wrote:
> > but remember, somehow this is defining that "printk.time" is a valid
> > ^
> > boot-time parameter, and i just didn't know you could do that without
> > writing an actual module. i guess i'll just take a closer look at the
> > contents of moduleparam.h to see how this is being done.
>
> yeah, actually I have to thank you, because I didn't know about it
> before :)
you're welcome. but i'm still confused as to how that code in
kernel/printk.c ends up defining a boot-time parameter named
"printk.time". i'm still open to suggestions.
rday
p.s. i can *sort of* follow the logic. in kernel/printk.c, we have
...
#if defined(CONFIG_PRINTK_TIME)
static int printk_time = 1;
#else
static int printk_time = 0;
#endif
module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
...
next, in moduleparam.h, we have:
...
#ifdef MODULE
#define MODULE_PARAM_PREFIX /* empty */
#else
#define MODULE_PARAM_PREFIX KBUILD_MODNAME "."
#endif
...
which, because that source file is not being built as a module, will
define MODULE_PARAM_PREFIX with the KBUILD_MODNAME value, which i'm
assuming is simply the basename of the source file -- "printk".
so i'm convinced that, if i follow the logic far enough, the
combination of the above will, in fact, define a boot-time parameter
whose name is "printk.time", even though there is no actual "module"
source file named printk.c.
here's an easier question -- given that we *know* that that boot-time
parameter *must* be defined for the kernel, can we use readelf or
objdump to display its existence in a newly-built kernel? i would
have thought it would have been placed in the "__param" section but i
don't see it there. thoughts?
--
========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry:
Have classroom, will lecture.
http://crashcourse.ca Waterloo, Ontario, CANADA
========================================================================
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