Tony, Have you checked the IA64 ABI? I remember there being a section talking about the state in which signal handlers should be started. I don't remember off hand if it said anything about psr.ac. --david On 11/14/08, Luck, Tony <tony.luck@xxxxxxxxx> wrote: > GLOBAL_ENTRY(kernel_execve) > + rum IA64_PSR_AC > mov r15=__NR_execve // put syscall number in place > break __BREAK_SYSCALL > br.ret.sptk.many rp > > I'm not overly happy with this because I still don't understand how > the PSR.ac bit became set in this context. This patch papers > over the problem by clearing psr.ac ... but it shouldn't be > set at this point! > > As far as I can see usage of psr.ac is as follows: > > 1) When Linux first boots the code in head.S transitions to > virtual mode ... this code sets PSR.ac=0. > > 2) Eight of the code paths in ivt.S set PSR.ac=1 before > transitioning to C code. Thus interrupt handlers, page faults > and other traps are executed with .ac=1. This is controlled by the > PSR_DEFAULT_BITS define ... which is (and I think always has) > been defined to set psr.ac. > > [I'm a bit puzzled as to why we want strict alignment checking > in interrupt/fault handlers, but are satisfied with more relaxed > behaivour in base code] > > I'm also puzzled why this issue only just surfaced, and why I > only see it on generic kernels. > > The problem may be related to some interrupt behavior. If I > tweak just the "__interrupt" code to not set psr.ac (but leave > the other seven fault handlers setting psr.ac=1) then I don't > see any unaligned traps in early init code. > > -Tony > > -- > To unsubscribe from this list: send the line "unsubscribe linux-ia64" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- Mosberger Consulting LLC, http://www.mosberger-consulting.com/ -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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