Project

General

Profile

KernelBuild » History » Version 31

Wolfgang Wiedmeyer, 05/08/2017 08:02 AM
link to release key page (key should be fetched from a keyserver if possible)

1 28 Wolfgang Wiedmeyer
h1. Kernel Build
2 1 Denis 'GNUtoo' Carikli
3 2 Denis 'GNUtoo' Carikli
h2. Use case
4
5 29 Wolfgang Wiedmeyer
Building a kernel aside Replicant is faster to set up and faster to build since you do not need to fetch and use the huge Android build system.
6 2 Denis 'GNUtoo' Carikli
7 30 Wolfgang Wiedmeyer
Users wanting to add a driver to their kernel, or developers that want to work on kernel related areas can do that to speed up the development process. If the changes are integrated back into Replicant, they will automatically be built by the Android build system when building images.
8 2 Denis 'GNUtoo' Carikli
9 4 Denis 'GNUtoo' Carikli
h2. Dependencies 
10 1 Denis 'GNUtoo' Carikli
11 30 Wolfgang Wiedmeyer
Since you are not compiling any user space applications, you don't need the Android build system. The Linux kernel and bootloaders such as U-Boot can be built without the Android build system.
12 4 Denis 'GNUtoo' Carikli
13 12 Denis 'GNUtoo' Carikli
The Trisquel ARM version of gcc seem to work well. To install it run:
14
<pre>
15
$ apt-get install gcc-arm-none-eabi
16
</pre>
17 4 Denis 'GNUtoo' Carikli
18 30 Wolfgang Wiedmeyer
If you use distributions such as Parabola, this will probably not work because the arm-none-eabi-gcc is too recent for many device kernels. But there are efforts to make the kernel sources compatible with more recent compiler versions.
19 1 Denis 'GNUtoo' Carikli
20 30 Wolfgang Wiedmeyer
You can install Trisquel in a container to work around this.
21
This way, it will have very few CPU and memory overhead compared to a virtual machine.
22 4 Denis 'GNUtoo' Carikli
It will also save disk space since you can just store the Trisquel rootfs in any directory.
23
24 10 Denis 'GNUtoo' Carikli
h2. Example with crespo under Trisquel
25 1 Denis 'GNUtoo' Carikli
26 10 Denis 'GNUtoo' Carikli
h3. Getting the right parameters
27
28 31 Wolfgang Wiedmeyer
First download the following example image and its signature:
29 27 Wolfgang Wiedmeyer
* https://ftp-osl.osuosl.org/pub/replicant/images/replicant-4.2/0004/images/crespo/replicant-4.2-crespo.zip.asc
30 1 Denis 'GNUtoo' Carikli
* https://ftp-osl.osuosl.org/pub/replicant/images/replicant-4.2/0004/images/crespo/replicant-4.2-crespo.zip
31
32 31 Wolfgang Wiedmeyer
As usual, verify the signature after [[ReplicantReleaseKey#Replicant-42-and-below|importing the release key]]:
33 6 Denis 'GNUtoo' Carikli
<pre>
34 31 Wolfgang Wiedmeyer
$ gpg --armor --verify path/to/replicant-4.2-crespo.zip.asc path/to/replicant-4.2-crespo.zip
35 6 Denis 'GNUtoo' Carikli
</pre>
36 31 Wolfgang Wiedmeyer
37
Make sure the check succeeds!
38 5 Denis 'GNUtoo' Carikli
39 7 Denis 'GNUtoo' Carikli
Then unpack the zip file:
40
<pre>
41 8 Denis 'GNUtoo' Carikli
$ mkdir replicant-4.2-crespo && cd replicant-4.2-crespo && unzip ../replicant-4.2-crespo.zip
42 7 Denis 'GNUtoo' Carikli
</pre>
43
44 9 Denis 'GNUtoo' Carikli
That should have extracted a boot.img. We then should not forget to look at what format the boot.img is in:
45
<pre>
46
$ file boot.img
47 1 Denis 'GNUtoo' Carikli
boot.img: Android bootimg, kernel (0x30008000), ramdisk (0x31000000), page size: 4096, cmdline (console=ttyFIQ0 no_console_suspend)
48
</pre>
49
Here it says it's an "Android bootimg", so we need the following tools:
50 10 Denis 'GNUtoo' Carikli
* mkbootimg to pack an image 
51
* unbootimg to unpack an image
52
53
Ways to get such tools:
54 27 Wolfgang Wiedmeyer
* Pre-built by Replicant at https://ftp-osl.osuosl.org/pub/replicant/images/replicant-4.2/0004/tools/
55 10 Denis 'GNUtoo' Carikli
* Build Replicant and use its tools. That defeat the purpose here since we want to avoid building Replicant fully.
56
57
Some android tools were converted to build on GNU/Linux without requiring the Android build system.
58
* In git://git.freesmartphone.org/utilities.git you have adb in android/adb, mkbootimg and unbootimg in android/image-utils
59
60
Some GNU/Linux distributions also have packages for some of the tools.
61 9 Denis 'GNUtoo' Carikli
62 19 Denis 'GNUtoo' Carikli
Extract the ramdisk and the kernel image and parameters from the original boot.img:
63
64 1 Denis 'GNUtoo' Carikli
<pre>
65 19 Denis 'GNUtoo' Carikli
$ unbootimg --kernel kernel.img --ramdisk ramdisk.img -i boot.img 
66 11 Denis 'GNUtoo' Carikli
total image size:   3100672
67
kernel size:        2903532
68
kernel load addr:   0x30008000
69
ramdisk size:       189142
70
ramdisk load addr:  0x31000000
71
2nd boot size:      0
72
2nd boot load addr: 0x30f00000
73
kernel tags addr:   0x30000100
74
page size:          4096
75
board:              `'
76
cmdline:            `console=ttyFIQ0 no_console_suspend'
77 1 Denis 'GNUtoo' Carikli
id:                 bd59d387bf083b0946e25a8f17f1aaef4bcc7412000
78 11 Denis 'GNUtoo' Carikli
</pre>
79 19 Denis 'GNUtoo' Carikli
80 22 Denis 'GNUtoo' Carikli
We also check the kernel image format, since we will build that:
81
<pre>
82
$ file kernel.img 
83
kernel.img: Linux kernel ARM boot executable zImage (little-endian)
84
</pre>
85 11 Denis 'GNUtoo' Carikli
86
h3. Building
87
88 14 Denis 'GNUtoo' Carikli
If you want to be able to run "make menuconfig", install libncurses5-dev:
89
<pre>
90
# apt-get install libncurses5-dev
91
</pre>
92
93 13 Denis 'GNUtoo' Carikli
Download the sources:
94 11 Denis 'GNUtoo' Carikli
<pre>
95 4 Denis 'GNUtoo' Carikli
$ git clone https://git.replicant.us/replicant/kernel_samsung_crespo.git
96 1 Denis 'GNUtoo' Carikli
</pre>
97 13 Denis 'GNUtoo' Carikli
98
Then in each console you build from, do:
99
<pre>
100
export ARCH=arm
101
export CROSS_COMPILE=arm-none-eabi-
102
</pre>
103
104
Configure it for crespo:
105
<pre>
106
$ make crespo_defconfig
107
</pre>
108
109 14 Denis 'GNUtoo' Carikli
If you want to configure it furthurer:
110
<pre>
111
$ make menuconfig
112
</pre>
113
114 13 Denis 'GNUtoo' Carikli
Then build a zImage:
115
<pre>
116
$ make -j4 zImage
117
</pre>
118 11 Denis 'GNUtoo' Carikli
119 15 Denis 'GNUtoo' Carikli
If the compilation succedded, the image is at:
120
<pre>
121
arch/arm/boot/zImage
122
</pre>
123
124
h3. Building Failures
125
126
Many devices specific kernels often contains not very clean code. This is very common with high volume devices due to time to market constraints. Upstream Linux has way higher code quality standards, but having your patches merged there requires more time.
127
128
As a result, variations in the default kernel configuration for your device can result in build errors.
129
130
Compilation failures can also happen when you use another gcc version, like we do in this guide.
131
This happens frequently if you use a gcc that is more recent than your kernel.
132
The "not very clean code" also increase the probability of it.
133
134 20 Denis 'GNUtoo' Carikli
h3. Repacking
135 21 Denis 'GNUtoo' Carikli
136 23 Denis 'GNUtoo' Carikli
We now create a new boot.img from the parameters and ramdisk.img we extracted from the default boot.img
137
<pre>
138
$ mkbootimg --kernel /path/to/arch/arm/boot/zImage --ramdisk ramdisk.img --cmdline "console=ttyFIQ0 no_console_suspend" --base 0x30000000 --pagesize 4096 -o new-boot.img
139
</pre>
140
141
Then we verify that it matches the default boot.img parameters:
142
<pre>
143
$ unbootimg -i new-boot.img 
144
total image size:   3096576
145
kernel size:        2899584
146
kernel load addr:   0x30008000
147
ramdisk size:       189142
148
ramdisk load addr:  0x31000000
149
2nd boot size:      0
150
2nd boot load addr: 0x30f00000
151
kernel tags addr:   0x30000100
152
page size:          4096
153
board:              `'
154
cmdline:            `console=ttyFIQ0 no_console_suspend'
155
id:                 f33faefb7b1eca7d1d1d6dc7603aed2bd82d65c000
156
</pre>
157
158
Here we check if the following parameters match:
159
* kernel load addr
160
* ramdisk load addr
161
* Kernel tag addr
162
* page size
163
* cmdline if you don't plan to change it.
164
165 1 Denis 'GNUtoo' Carikli
h3. Testing
166 24 Denis 'GNUtoo' Carikli
167
Reboot the device to the bootloader, and run:
168
<pre>
169
$ fastboot boot new-boot.img
170 25 Denis 'GNUtoo' Carikli
< waiting for device >
171
downloading 'boot.img'...
172
OKAY [  0.435s]
173
booting...
174
OKAY [  0.288s]
175
finished. total time: 0.723s
176 24 Denis 'GNUtoo' Carikli
</pre>