Re: [Ltib] Forcing DEBUG for pr_debug in kernel driver through LTIB

[Michael Jones]

Franz Trierweiler wrote:
> Stuart Hughes a écrit :
> > Hi Franz,
> >
> > As far as ltib goes, you can do: ./ltib -p kernel -c and that will 
> > unpack the kernel sources and drop you to the kernel config screen.  
> > If the kernel config system has a configuration point to set 
> > KERN_DEBUG then you can set it there, save and exit and the kernel 
> > will build.  If there is no config point for it, you'll have to edit 
> > the file manually.
> >
> > Regards, Stuart
> >
> > Franz Trierweiler wrote:
> > > Hello everybody
> > >
> > > Freescale has just issued a new PDK (PDK 1.6) for the iMX25 3-stack 
> > > evalboard. I have hardwired a SIM interface to my evalboard so that I 
> > > can scope all electrical signals coming from that cell. The fact is 
> > > that I am trying to debug the mxc_sim.c source file for this SIM 
> > > interface. mxc_sim is a SIM driver. In order to achieve this, I would 
> > > like to enable pr_debug (...) output to my console when this driver 
> > > is running and watch all debug messages displayed.
> > >
> > > The kernel.h shows the pr_debug macro like this:
> > >
> > > /* If you are writing a driver, please use dev_dbg instead */
> > > #if defined(CONFIG_DYNAMIC_PRINTK_DEBUG)
> > > #define pr_debug(fmt, ...) do { \
> > >    dynamic_pr_debug(pr_fmt(fmt), ##__VA_ARGS__); \
> > >    } while (0)
> > > #elif defined(DEBUG)
> > > #define pr_debug(fmt, ...) \
> > >    printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
> > > #else
> > > #define pr_debug(fmt, ...) \
> > >    ({ if (0) printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__); 0; })
> > > #endif
> > >
> > > There seems that if I #define DEBUG somewhere then I will have the 
> > > messages displayed (or logged) somewhere.
> > >
> > > Is there a way of doing this properly in the LTIB configuration when 
> > > recompiling the kernel ?
> > >
> > > Or should I simply #define DEBUG in kernel.h? (This really does not 
> > > sound the right way).
> > >
> > > Or should I simply put DEBUG=ON (or something like this) in the LTIB 
> > > perl script? (sounds also very dirty).
> > >
> > > I really would like to make this in a clean way.
> > >
> > > Regards,
> > > Franz
> Hi Stuart,
>
> There is no configuration point for KERN_DEBUG but I found a few 
> references to DEBUG in 
> ~/ltib/config/platform/imx/imx25_3stack_defconfig.dev
>
> #
> # Kernel hacking
> #
> # CONFIG_PRINTK_TIME is not set
> CONFIG_ENABLE_WARN_DEPRECATED=y
> CONFIG_ENABLE_MUST_CHECK=y
> CONFIG_FRAME_WARN=1024
> # CONFIG_MAGIC_SYSRQ is not set
> # CONFIG_UNUSED_SYMBOLS is not set
> # CONFIG_DEBUG_FS is not set
> # CONFIG_HEADERS_CHECK is not set
> # CONFIG_DEBUG_KERNEL is not set
> # CONFIG_DEBUG_BUGVERBOSE is not set
> # CONFIG_DEBUG_MEMORY_INIT is not set
> CONFIG_FRAME_POINTER=y
> # CONFIG_RCU_CPU_STALL_DETECTOR is not set
> # CONFIG_LATENCYTOP is not set
> CONFIG_SYSCTL_SYSCALL_CHECK=y
> CONFIG_HAVE_FUNCTION_TRACER=y
>
> It is recommended not to edit this file. Thus, I suspect there is a 
> clean way of configuring CONFIG_DEBUG_KERNEL through LTIB. I invoked 
> ltib with --configure and chose "Configure the kernel" (as usual) but 
> never was successful in finding the corresponding options. The 
> --configure option makes changes in 
> ~/ltib/config/platform/imx/imx25_3stack_defconfig.dev, thus I suspect I 
> am not too far from what I am looking for.
>
> I will try to modify the file by hand.
>
> Regards,
> Franz
>
>
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Hi Franz,

That is a kernel config file, not an LTIB config file, so there must be 
a configuration point for it in the kernel config menu, not the LTIB 
config.  You can type slash in the kernel config menu to search for a 
particular CONFIG_ option, e.g. "/DEBUG_KERNEL".  Then you'll see where 
it's defined in the sources and where it is buried in the menu.

In my kernel (2.6.23), this is located in the "Kernel hacking" submenu 
of the kernel config menu.  It looks like it's still there in 2.6.31, 
too.  However, I think DEBUG_KERNEL only makes it possible to enable 
some other DEBUG options which are in their own menus and Makefiles.  I 
would work the other way around though and look in the Makefile which 
builds mxc_sim.c.  If there are a few lines like e.g.

ifeq ($(CONFIG_DEBUG_MXC_SIM_DRIVER),y)
EXTRA_CFLAGS += -DDEBUG
endif

then you would need to hunt down CONFIG_DEBUG_MXC_SIM_DRIVER in the 
kernel config.  If there's no mention of "-DDEBUG" at all in your 
mxc_sim.c's Makefile, then you're probably left with #define'ing it 
yourself in the sources (but consider doing it in mxc_sim.c before 
including kernel.h and not directly in kernel.h).

sincerely,
Michael

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