Messages in this thread Patch in this message | | | Date | Fri, 4 Aug 2006 18:56:11 -0400 | From | Vivek Goyal <> | Subject | Re: [RFC] ELF Relocatable x86 and x86_64 bzImages |
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On Tue, Aug 01, 2006 at 04:58:49AM -0600, Eric W. Biederman wrote: > > The problem: > > We can't always run the kernel at 1MB or 2MB, and so people who need > different addresses must build multiple kernels. The bzImage format > can't even represent loading a kernel at other than it's default address. > With kexec on panic now starting to be used by distros having a kernel > not running at the default load address is starting to become common. > Hi Eric,
There seems to be a small anomaly in the current set of patches for i386.
For example if one compiles the kernel with CONFIG_RELOCATABLE=y and CONFIG_PHYSICAL_START=0x400000 (4MB) and he uses grub to load the kernel then kernel would run from 1MB location. I think user would expect it to run from 4MB location.
I think distro's might want to keep above config options enabled. CONFIG_RELOCATABLE=y so that kexec can load kdump kernel at a different address and CONFIG_PHYSICAL_START=non 1MB location, to extract better performance. (As we had discussions on mailing list some time back.)
In principle this is a limitation on boot-loaders part but as we can not fix the boot-loaders out there, probably we can try fixing it at kernel level.
What I have done here is that decompressor code will determine the final resting place of the kernel based on boot loader type. So if I have been loaded by kexec, I am supposed to run from loaded address otherwise I am supposed to run from CONFIG_PHYSICAL_START as I have been loaded at 1MB address due to boot loader limitation and that's not the intention.
A prototype patch is attached with the mail. I have assumed that I can assign a boot loader type id 9 to kexec (Documentation/i386/boot.txt). Also assuming that all other boot loaders apart from kexec have got 1MB limitation. If not, its trivial to include their boot loader ids also.
I have tested this patch and it works fine. What do you think about this approach ?
Thanks Vivek
Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com> ---
arch/i386/boot/compressed/head.S | 32 ++++++++++++++++++++++++++++++-- 1 file changed, 30 insertions(+), 2 deletions(-)
diff -puN arch/i386/boot/compressed/head.S~debug1-patch arch/i386/boot/compressed/head.S --- linux-2.6.18-rc3-1M/arch/i386/boot/compressed/head.S~debug1-patch 2006-08-04 18:03:02.000000000 -0400 +++ linux-2.6.18-rc3-1M-root/arch/i386/boot/compressed/head.S 2006-08-04 18:18:26.000000000 -0400 @@ -60,13 +60,32 @@ startup_32: * a relocatable kernel this is the delta to our load address otherwise * this is the delta to CONFIG_PHYSICAL start. */ + #ifdef CONFIG_RELOCTABLE + /* If loaded by non kexec boot loader, then we will be loaded + * at 1MB fixed address. But probably the intention is to run + * from a address for which kernel has been compiled which can + * be non 1MB. + */ + xorl %eax, %eax + movb 0x210(%esi), %al + + / * check boot loader type. Kexec bootloader id 9, version any */ + shrl $4, %eax + subl $0x9, %eax + jnz 1f + + /* Run kernel from the location it has been loaded at. */ movl %ebp, %ebx + jmp 2f + + /* Run the kernel from compiled destination location. */ +1: movl $(CONFIG_PHYSICAL_START - startup32), %ebx #else movl $(CONFIG_PHYSICAL_START - startup_32), %ebx #endif - /* Replace the compressed data size with the uncompressed size */ +2: /* Replace the compressed data size with the uncompressed size */ subl input_len(%ebp), %ebx movl output_len(%ebp), %eax addl %eax, %ebx @@ -95,7 +114,16 @@ startup_32: /* Compute the kernel start address. */ #ifdef CONFIG_RELOCATABLE + xorl %eax, %eax + movb 0x210(%esi), %al + / * check boot loader type. Kexec bootloader id 9, version any */ + shrl $4, %eax + subl $0x9, %eax + jnz 3f leal startup_32(%ebp), %ebp + jmp 4f +3: + movl $CONFIG_PHYSICAL_START, %ebp #else movl $CONFIG_PHYSICAL_START, %ebp #endif @@ -103,7 +131,7 @@ startup_32: /* * Jump to the relocated address. */ - leal relocated(%ebx), %eax +4: leal relocated(%ebx), %eax jmp *%eax .section ".text" relocated: _ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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