Minimum build config for boot messages

Minimum build config for boot messages

[Andre Schmidt]

Hello,

what is the minimum config to build a linux kernel that just prints boot messages/errors?

I was going through my old experiments/notes and found that we used to get kernel boot message with vanilla allnoconfig.

make ARCH=x86_64 allnoconfig
make all
qemu-system-x86_64 -kernel arch/x86/boot/bzImage

Those commands above used to be enough, but now the produced kernel doesn't print any messages on the qemu screen.

With some trial-and-error i was able to track down this commit
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/init/Kconfig?id=5d2acfc7b974bbd3858b4dd3f2cdc6362dd8843a
and if i add CONFIG_EMBEDDED=n to my KCONFIG_ALLCONFIG file, i can see kernel errors again.

I didn't investigate further cause i don't really know what i'm doing, but do wonder:

Can you reproduce this?
Is this (now) expected behavior?
(and it was luck before, to get kernel messages with vanilla allnoconfig)
Do we (now) need some specific option to enable kernel messages with allnoconfig?
(CONFIG_EMBEDDED=n sounds pretty generic and doesn't feel right)
Am i doing it all wrong? :D

Curiously,
Andre Schmidt

ps. i'm aware of defconfig, but i would like to experiment/learn from bottom-up, rather than top-down.

Minimum build config for boot messages

[John de la Garza]

On Fri, Aug 19, 2016 at 04:17:22PM +0200, Andre Schmidt wrote:
> make ARCH=x86_64 allnoconfig
> make all
> qemu-system-x86_64 -kernel arch/x86/boot/bzImage
> 
> Those commands above used to be enough, but now the produced kernel doesn't print any messages on the qemu screen.
> 
> With some trial-and-error i was able to track down this commit
> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/init/Kconfig?id=5d2acfc7b974bbd3858b4dd3f2cdc6362dd8843a
> and if i add CONFIG_EMBEDDED=n to my KCONFIG_ALLCONFIG file, i can see kernel errors again.
> (CONFIG_EMBEDDED=n sounds pretty generic and doesn't feel right)

> Can you reproduce this?

yes

> ps. i'm aware of defconfig, but i would like to experiment/learn from bottom-up, rather than top-down.

I've done the same and would have expected the the previous behavior,
too.

Minimum build config for boot messages

[Johannes Thoma]

Hi,

Am 19.08.16 um 16:17 schrieb Andre Schmidt:
 > Hello,
 >
 > what is the minimum config to build a linux kernel that just prints 
boot messages/errors?
 >
 > I was going through my old experiments/notes and found that we used 
to get kernel boot message with vanilla allnoconfig.
 >
 > make ARCH=x86_64 allnoconfig
 > make all
 > qemu-system-x86_64 -kernel arch/x86/boot/bzImage
 >
 > Those commands above used to be enough, but now the produced kernel 
doesn't print any messages on the qemu screen.
 >

Did you also disable CONFIG_PRINTK ? Without that kernel will not print 
anything, as far as I know.

HTH,

Best,

- Johannes

Minimum build config for boot messages

[Andre Schmidt]

On Mon, 22 Aug 2016 20:50:49 +0200
Johannes Thoma <johannes@johannesthoma.com> wrote:

> Did you also disable CONFIG_PRINTK ? Without that kernel will not print 
> anything, as far as I know.

hmm,

i tried with following:

CONFIG_PRINTK=y
CONFIG_EARLY_PRINTK=y

both adding through KCONFIG_ALLCONFIG and `make menuconfig`. still no kernel messages :/

FWIW, heres the `diffconfig` of adding above with `make menuconfig` over allnoconfig:

 EARLY_PRINTK n -> y
 PRINTK n -> y
+BOOT_PRINTK_DELAY n
+LOG_BUF_SHIFT 17
+NMI_LOG_BUF_SHIFT 13
+PRINTK_NMI y
+PRINTK_TIME n

i assume something is still missing (from the 289 changes that CONFIG_EMBEDDED=n does over allnoconfig).

Cheers
Andre Schmidt