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i spent a fair amount of time chasing a 64-bit bootup crash that manifested itself as bootup segfaults: S10network[1825]: segfault at 7f3e2b5d16b8 ip 00000031108748c9 sp 00007fffb9c14c70 error 4 in libc-2.7.so[3110800000+14d000] eventually causing init to die and panic the system: Kernel panic - not syncing: Attempted to kill init! Pid: 1, comm: init Not tainted 2.6.26-rc9-tip #13878 after a maratonic bisection session, the bad commit turned out to be: | b7675791859075418199c7af86a116ea34eaf5bd is first bad commit | commit b7675791859075418199c7af86a116ea34eaf5bd | Author: Jeremy Fitzhardinge <jeremy@goop.org> | Date: Wed Jun 25 00:19:00 2008 -0400 | | x86: remove open-coded save/load segment operations | | This removes a pile of buggy open-coded implementations of savesegment | and loadsegment. after some more bisection of this patch itself, it turns out that what makes the difference are the savesegment() changes to __switch_to(). Taking a look at this portion of arch/x86/kernel/process_64.o revealed this crutial difference: | good: 99c: 8c e0 mov %fs,%eax | 99e: 89 45 cc mov %eax,-0x34(%rbp) | | bad: 99c: 8c 65 cc mov %fs,-0x34(%rbp) which is due to: | unsigned fsindex; | - asm volatile("movl %%fs,%0" : "=r" (fsindex)); | + savesegment(fs, fsindex); savesegment() is implemented as: #define savesegment(seg, value) \ asm("mov %%" #seg ",%0":"=rm" (value) : : "memory") note the "m" modifier - it allows GCC to generate the segment move into a memory operand as well. But regarding segment operands there's a subtle detail in the x86 instruction set: the above 16-bit moves are zero-extend, but only if it goes to a register. If it goes to a memory operand, -0x34(%rbp) in the above case, there's no zero-extend to 32-bit and the instruction will only save 16 bits instead of the intended 32-bit. The other 16 bits is random data - which can cause problems when that value is used later on. The solution is to only allow segment operands to go to registers. This fix allows my test-system to boot up without crashing. Signed-off-by: Ingo Molnar <mingo@elte.hu> |
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| acpi | ||
| asm-alpha | ||
| asm-arm | ||
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| asm-blackfin | ||
| asm-cris | ||
| asm-frv | ||
| asm-generic | ||
| asm-h8300 | ||
| asm-ia64 | ||
| asm-m32r | ||
| asm-m68k | ||
| asm-m68knommu | ||
| asm-mips | ||
| asm-mn10300 | ||
| asm-parisc | ||
| asm-powerpc | ||
| asm-ppc | ||
| asm-s390 | ||
| asm-sh | ||
| asm-sparc | ||
| asm-sparc64 | ||
| asm-um | ||
| asm-v850 | ||
| asm-x86 | ||
| asm-xtensa | ||
| crypto | ||
| keys | ||
| linux | ||
| math-emu | ||
| media | ||
| mtd | ||
| net | ||
| pcmcia | ||
| rdma | ||
| rxrpc | ||
| scsi | ||
| sound | ||
| video | ||
| xen | ||
| Kbuild | ||