Messages in this thread | | | Date | Sun, 20 Jan 2013 22:55:05 +0100 | From | Thomas Capricelli <> | Subject | Kernel failing to boot when compressed with bzip2 |
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Hello,
I have had this weird behaviour that seems to be important enough to report on lkml. I compile my own kernels since ~1994 and never had this bug before. There are actually two problems :
1st problem Since around September 2012, i have tried to compile my kernel 3.6.x with gcc-4.7. It failed this way: just after grub loaded the kernel, after displaying "Decompressing Linux", the computer rebooted. The exact same kernel (same .config) compiled with gcc-4.6 would boot perfectly. I did several tests, it was all very reproducible. I didn't pay attention and just stick with gcc-4.6 when compiling my kernel. I thought it would just get fixed with time.
2nd problem Then the kernel 4.7 was released. I started testing with 4.7.1, did the usual stuff and obviously, I used gcc-4.6, because of the previous problem. Guess what, I've had _exactly_ the same behaviour. I double checked and again i could reproduce it very well: kernel 3.6 / gcc 4.6 -> OK kernel 3.7 / gcc 4.6 -> reboot after printing "Decompressing Linux" kernel 3.6 / gcc 4.7 -> reboot after printing "Decompressing Linux"
It took some time to find out the source of the problem, which will probably feel obvious to many of you: a long time ago, i had switched from using CONFIG_KERNEL_GZIP to using CONFIG_KERNEL_BZIP2, probably just for the fun of testing it. I can't remember when but it was probably very long ago (2 years ?).
Testing confirmed : going back to CONFIG_KERNEL_GZIP fixed it all and i could not only use gcc-4.7 but also kernel 4.7.
So my guess is that there's something badly broken in the bzip2 kernel decompressing code.. ? There's both a regression between kernel 3.6 and 3.7, and a problem with gcc-4.7.
Here are some more information, just ask if you need some more. I can even do some testing, but you'll need to cc: me as i'm not anymore on lkml.
* the cpu is "AMD Athlon(tm) II X4 620 Processor" as reported by /proc/cpuinfo * CONFIG_DECOMPRESS_BZIP2=y was set on all my tests (not sure it's relevant) * the last 3.6 kernel tested was 3.6.11 * 4.7 kernels tested were 4.7.1, 4.7.2, and 4.7.3 * the computer will reboot really fast just after the kernel kprinted "Decompressing Linux", nothing is kprinted after this.
best regards,
-- Thomas Capricelli <orzel@freehackers.org> http://www.freehackers.org/thomas/
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