[lkml]   [2020]   [Mar]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [RFC PATCH] dynamic_debug: Add config option of DYNAMIC_DEBUG_CORE

On 3/19/20 11:28 AM, Orson Zhai wrote:
> Hi Jason,
> On Wed, Mar 18, 2020 at 05:18:43PM -0400, Jason Baron wrote:
>> On 3/18/20 3:03 PM, Orson Zhai wrote:
>>> There is the requirement from new Android that kernel image (GKI) and
>>> kernel modules are supposed to be built at differnet places. Some people
>>> want to enable dynamic debug for kernel modules only but not for kernel
>>> image itself with the consideration of binary size increased or more
>>> memory being used.
>>> By this patch, dynamic debug is divided into core part (the defination of
>>> functions) and macro replacement part. We can only have the core part to
>>> be built-in and do not have to activate the debug output from kenrel image.
>>> Signed-off-by: Orson Zhai <>
>> Hi Orson,
>> I think this is a nice feature. Is the idea then that driver can do
>> something like:
>> #define driver_foo_debug(fmt, ...) \
>> dynamic_pr_debug(fmt, ##__VA_ARGS__)
>> #else
>> no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
>> #enif
>> And then the Kconfig:
>> bool "Enable dynamic driver foo printk() support"
> I highly appreciate you for giving this good example to us.
> To be honest I did not really think of this kind of usage. :)
> But it makes much sense. I think dynamic debug might be a little
> bit high for requirement of memory. Every line of pr_debug will be
> added with a static data structure and malloc with an item in link table.
> It might be sensitive especially in embeded system.
> So this example shows how to avoid to turn on dynamci debug for whole
> system but part of it when being needed.
>> Or did you have something else in mind? Do you have an example
>> code for the drivers that you mention?
> My motivation comes from new Andorid GKI release flow. Android kernel team will
> be in charge of GKI release. And SoC vendors will build their device driver as
> kernel modules which are diffrent from each vendor. End-users will get their phones
> installed with GKI plus some modules all together.
> So at Google side, they can only set DYNAMIC_DEBUG_CORE in their defconfig to build
> out GKI without worrying about the kernel image size increased too much. Actually
> GKI is relatively stable as a common binary and there is no strong reason to do
> dynamic debugging to it.
> And at vendor side, they will use a local defconfig which is same with Google one but add
> CONFIG_DYNAMIC_DEBUG to build their kenrel modules. As DYNAMIC_DEBUG enables only a
> set of macro expansion, so it has no impact to kernel ABI or the modversion.
> All modules will be compatible with GKI and with dynamic debug enabled.
> Then the result will be that Google has his clean GKI and vendors have their dynamic-debug-powered modules.

static int __init dynamic_debug_init(void)
struct _ddebug *iter, *iter_start;
const char *modname = NULL;
char *cmdline;
int ret = 0;
int n = 0, entries = 0, modct = 0;
int verbose_bytes = 0;

if (__start___verbose == __stop___verbose) {
pr_warn("_ddebug table is empty in a CONFIG_DYNAMIC_DEBUG build\n");
return 1;


I wonder if we should just remove it now.



 \ /
  Last update: 2020-03-19 21:20    [W:0.063 / U:1.576 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site