| Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | BTFIXUP |
| 2 | ------- |
| 3 | |
| 4 | To build new kernels you have to issue "make image". The ready kernel |
| 5 | in ELF format is placed in arch/sparc/boot/image. Explanation is below. |
| 6 | |
| 7 | BTFIXUP is a unique feature of Linux/sparc among other architectures, |
| 8 | developed by Jakub Jelinek (I think... Obviously David S. Miller took |
| 9 | part, too). It allows to boot the same kernel at different |
| 10 | sub-architectures, such as sun4c, sun4m, sun4d, where SunOS uses |
| 11 | different kernels. This feature is convinient for people who you move |
| 12 | disks between boxes and for distrution builders. |
| 13 | |
| 14 | To function, BTFIXUP must link the kernel "in the draft" first, |
| 15 | analyze the result, write a special stub code based on that, and |
| 16 | build the final kernel with the stub (btfix.o). |
| 17 | |
| 18 | Kai Germaschewski improved the build system of the kernel in the 2.5 series |
| 19 | significantly. Unfortunately, the traditional way of running the draft |
| 20 | linking from architecture specific Makefile before the actual linking |
| 21 | by generic Makefile is nearly impossible to support properly in the |
| 22 | new build system. Therefore, the way we integrate BTFIXUP with the |
| 23 | build system was changed in 2.5.40. Now, generic Makefile performs |
| 24 | the draft linking and stores the result in file vmlinux. Architecture |
| 25 | specific post-processing invokes BTFIXUP machinery and final linking |
| 26 | in the same way as other architectures do bootstraps. |
| 27 | |
| 28 | Implications of that change are as follows. |
| 29 | |
| 30 | 1. Hackers must type "make image" now, instead of just "make", in the same |
| 31 | way as s390 people do now. It is analogous to "make bzImage" on i386. |
| 32 | This does NOT affect sparc64, you continue to use "make" to build sparc64 |
| 33 | kernels. |
| 34 | |
| 35 | 2. vmlinux is not the final kernel, so RPM builders have to adjust |
| 36 | their spec files (if they delivered vmlinux for debugging). |
| 37 | System.map generated for vmlinux is still valid. |
| 38 | |
| 39 | 3. Scripts that produce a.out images have to be changed. First, if they |
| 40 | invoke make, they have to use "make image". Second, they have to pick up |
| 41 | the new kernel in arch/sparc/boot/image instead of vmlinux. |
| 42 | |
| 43 | 4. Since we are compliant with Kai's build system now, make -j is permitted. |
| 44 | |
| 45 | -- Pete Zaitcev |
| 46 | zaitcev@yahoo.com |