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Date: Thu, 2 Mar 2017 19:04:41 -0800 From: Guenter Roeck <linux@...ck-us.net> To: Tobias Klauser <tklauser@...tanz.ch> Cc: Sven Schmidt <4sschmid@...ormatik.uni-hamburg.de>, Sandra Loosemore <sandra@...esourcery.com>, Arnd Bergmann <arnd@...db.de>, Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, Ley Foon Tan <lftan@...era.com>, nios2-dev@...ts.rocketboards.org Subject: Re: nios2 crash/hang in mainline due to 'lib: update LZ4 compressor module' On 03/02/2017 08:38 AM, Tobias Klauser wrote: > On 2017-03-01 at 20:45:21 +0100, Guenter Roeck <linux@...ck-us.net> wrote: >> On Wed, Mar 01, 2017 at 07:58:17PM +0100, Sven Schmidt wrote: >>> Hi Guenter, Tobias and Sandra, >>> >>> thanks for your effort here. >>> >>> On Tue, Feb 28, 2017 at 10:14:13AM -0800, Guenter Roeck wrote: >>>> On Tue, Feb 28, 2017 at 10:53:56AM -0700, Sandra Loosemore wrote: >>>>> On 02/28/2017 08:53 AM, Tobias Klauser wrote: >>>>>> (adding Sandra Loosemore to Cc due to possible relation to gcc/binutils >>>>>> for nios2) >>>>>> >>>>>> On 2017-02-26 at 22:03:38 +0100, Guenter Roeck <linux@...ck-us.net> wrote: >>>>>>> Hi Sven, >>>>>>> >>>>>>> my qemu test for nios2 started failing with commit 4e1a33b105dd ("lib: >>>>>>> update LZ4 compressor module"). The test hangs early during boot before >>>>>>> any console output is seen. Reverting the offending patch as well as the >>>>>>> subsequent lz4 related patches fixes the problem. Disabling CONFIG_RD_LZ4 >>>>>>> and with it other LZ4 options also fixes it (as does adding "return -EINVAL;" >>>>>>> at the top of the LZ4 decompression code). For reference, bisect log >>>>>>> is attached. >>>>>>> >>>>>>> I tried with buildroot toolchains using gcc 6.1.0 as well as 6.3.0 >>>>>>> and binutils 2.26.1. Scripts used to run the tests are available at >>>>>>> https://github.com/groeck/linux-build-test/tree/master/rootfs/nios2. >>>>>>> Qemu is from qemu mainline or qemu v2.8 with nios2 patches applied. >>>>>> >>>>>> Looks like this is somehow related to gcc/binutils. Using GCC 4.8.3 and >>>>>> binutils 2.24.51 (both from from Sourcery CodeBench Lite 2014.05) I can >>>>>> get a kernel booting on latest master branch. AFAICT, none of the >>>>>> LZ4_decompress_* functions are called during boot. >>>>>> >>> >>> It seems a bit strange that code which is not actually called causes problems like that. >>> >> Yes, it is, though it is always possible. The code isn't exactly easy to >> understand; there may be some hidden caveats such as global variables. It may >> also be that some jump target exceeds its range (though why that would only >> be seen with the LZ4 code is another question), or that the compiler gets >> confused by the forced inlines (disabling that didn't make a difference, >> though, nor did disabling -O3). >> >>> Please let me know if and how I may help you figure out what's happening, especially >>> regarding the differences between the previous LZ4 and the current implementation. >>> >> >> For my part I am all but clueless. Unless someone has an idea, we may to >> disable LZ4 support for nios2 for the time being. Does anyone have thoughts >> on that ? Of course, that would not help if the problem also affects >> recent gcc/binutil versions on other architectures. > > After some further investigations, I'd say this isn't "caused" by LZ4 > specifically but by a more general problem with one of the nios2 arch > specific tools involved. > > I manually enabled random additional CONFIG_* options and in some cases > I got the kernel to boot (with CONFIG_RD_LZ4 enabled and no return > -EINVAL in place) while in others I didn't. So I'd rather suspect this > problem to be connected to the size or structure of the generated vmlinux > image. > > Or could this even be a problem with qemu? Did anyone already verify > this on the 10m50 devboard? (Unfortunately I don't have any nios2 > devboard available right now, otherwise I would have done this...) > That is of course always possible. > Other than that I'm also becoming all but clueless... One option I > thought of was using the QEMU monitor to dump the CPU state after the > hang but so far I didn't manage to get it to work (hints appreciated ;) > Something like qemu-system-nios2 -M 10m50-ghrd -kernel vmlinux -no-reboot \ -dtb arch/nios2/boot/dts/10m50_devboard.dtb \ --append "rdinit=/sbin/init" -initrd busybox-nios2.cpio gives you a qemu monitor window. Use "info registers" to see registers. Looks like it is stuck in init_bootmem_core, or at least that is what it shows for me. Guenter
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