Booting custom kernel on xeon-phi

0
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I am trying to boot a custom kernel on Xeon-phi instead of the default Linux kernel. At this link, I found a way to cross compile my kernel which compiles successfully using k1om-mpss-linux-gcc cross compiler. Is cross compiling enough ? I get the error

mykernel.img is not a k1om Linux bzImage

Edit: So, I used /usr/linux-k1om-4.7/bin/x86_64-k1om-linux-gcc compiler to compile a simple helloworld.c program and the kernel source. I get two different types of results for objdump -f on the executables.

for helloworld.c:

hello: file format elf64-k1om architecture: k1om, flags 0x00000112: EXEC_P, HAS_SYMS, D_PAGED start address 0x0000000000400400

for mykernel:

mykernel: file format elf32-i386 architecture: i386, flags 0x00000112: EXEC_P, HAS_SYMS, D_PAGED start address 0x0010000c

I compiled using the same compiler, yet they show different architectures. What is the reason for this ?

2
gcckernelcross-compilingxeon-phi
What version of MPSS are you using now, and which one did you compile? – Mark Lakata
I am using 3.4.2. What I am trying to do is replace the current linux kernel with another kernel. Now my kernel should require some patches, but I am unable to proceed as it is not giving any errors except that it doesn't recognize the image even after I have successfully cross compiled. – lipak

2 Answers

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The first thing to do is figure out what mykernel.img is. Try running file on it.

 $ file  /opt/mpss/3.4/sysroots/k1om-mpss-linux/boot/vmlinux-2.6.38.8+mpss3.4
 /opt/mpss/3.4/sysroots/k1om-mpss-linux/boot/vmlinux-2.6.38.8+mpss3.4: ELF 64-bit LSB executable, version 1 (SYSV), statically linked, BuildID[sha1]=0xa4c16ee85c11aca4e78dc4ae46d3827fb74289c1, not stripped

$ objdump -f /opt/mpss/3.4/sysroots/k1om-mpss-linux/boot/vmlinux-2.6.38.8+mpss3.4

/opt/mpss/3.4/sysroots/k1om-mpss-linux/boot/vmlinux-2.6.38.8+mpss3.4:     file format elf64-k1om
architecture: k1om, flags 0x00000112:
EXEC_P, HAS_SYMS, D_PAGED
start address 0x0000000001000000
0
votes

The answer to your original question - no, unfortunately, it is not as simple as just cross-compiling. There were a number of changes made to the kernel that comes with the MPSS. I don't know all the changes but a big one that I do know is that they had to add support for the larger register set on the coprocessor in order to be able to save state on a context switch.

As to why the file format is elf32-i386 instead of elf32-k1om -

The web site you referenced referred to recompiling the kernel that came with the MPSS after possibly make a few changes in the files. You'll notice that they also copied over a configuration file for the installed version of the kernel. So they had all the files to remake the kernel exactly as it had been made.

I suspect that, in your case, either a) there was a configuration script of some sort in your source directory that picked up the architecture you were running on and caused confusion when the makefile ran or b) your makefile had no idea what k1om was. In either case, it fell back to what it believed to the the lowest common denominator i386. As I say, this is just a suspicion on my part but a careful reading of your makefiles should lead to the answer.