On 02/28/2017 02:22 PM, David Daney wrote: > On 02/28/2017 11:05 AM, David Daney wrote: >> On 02/28/2017 10:39 AM, Jason Baron wrote: >>> > [...] >>>> I suspect that the alignment of the __jump_table section in the .ko >>>> files is not correct, and you are seeing some sort of problem due to >>>> that. >>>> >>>> >>> >>> Hi, >>> >>> Yes, if you look at the trace that Sachin sent the module being loaded >>> that does the WARN_ON() is nfsd.ko. >>> >>> That module from Sachin's trace has: >>> >>> [31] __jump_table PROGBITS 0000000000000000 03fd77 0000c0 >>> 18 WAM 0 0 1 >> >> The problem is then the section alignment (last column) for power. >> >> On mips with no patches applied, we get: >> >> [17] __jump_table PROGBITS 0000000000000000 00d2c0 000048 >> 00 WA 0 0 8 >> >> Look, proper alignment! >> >> The question I have is why do the power ".llong" and ".long" assembler >> directives not force section alignment? Is there an alternative that >> could be used that would result in the proper alignment? Would ".word" >> work? >> >> If not, then I would say patch only power with your balign thing. 8-byte >> alignment for 64-bit kernel, 4-byte alignment for 32-bit kernel >> > > I think the proper fix is either: > > A) Modify scripts/module-common.lds to force __jump_table alignment for > all architectures. > > B) Add arch/powerpc/kernel/module.lds to force __jump_table alignment > for powerpc only. > > David. > > Ok, I can try adding it to the linger script. FWIW, here is my before and after with the .balign thing for the nfsd.ko module on powperc (using a cross-compiler): before: [31] __jump_table PROGBITS 0000000000000000 03ee3e 0000f0 00 WA 0 0 1 after: [31] __jump_table PROGBITS 0000000000000000 03ee40 0000f0 00 WA 0 0 4 Thanks, -Jason > >> >>> >>> So its not the size but rather the start offset '03fd77', that is the >>> problem here. That is what the WARN_ON triggers on, that the start of >>> the table is not 4-byte aligned. >>> >>> Using a ppc cross-compiler and the ENTSIZE patch that line does not >>> change, however if I use the initial patch posted in this thread, the >>> start does align to 4-bytes and thus the warning goes away, as Sachin >>> verified. In fact, without the patch I found several modules that don't >>> start at the proper alignment, however with the patch that started this >>> thread they were all properly aligned. >>> >>> In terms of the '.balign' causing holes, we originally added the >>> '_ASM_ALIGN' to x86 for precisely this reason. See commit: >>> ef64789 jump label: Add _ASM_ALIGN for x86 and x86_64 and discussion. >>> >>> In addition, we have a lot of runtime with the .balign in the tree and >>> I'm not aware of any holes in the table. I think the code would blow up >>> pretty badly if there were. >>> >>> A number of arches were already using the '.balign', and the patch I >>> proposed simply added it to remaining ones, now that we added a >>> WARN_ON() to catch this condition. >>> >>> Thanks, >>> >>> -Jason >>> >>> >>> >>> >> >> >> _______________________________________________ >> linux-arm-kernel mailing list >> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx >> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >
