On Fri, Feb 14, 2014 at 03:24:09PM +0100, Stefan Bader wrote:
> Actually, this code just makes so much more sense if I let objdump do
> relocation info...
Ok, we're pretty sure you have an MFENCE there in resched_task but can
you confirm it please.
First, does /proc/cpuinfo have the "sse2" string? It should but nowadays
I don't trust anything.
Then, can you boot that kernel in qemu with the -gdb flag so that it
starts the gdb stub, here's the manpage about it:
-gdb dev
Wait for gdb connection on device dev. Typical connections will likely be
TCP-based, but also UDP, pseudo TTY, or even stdio are reasonable use case.
The latter is allowing to start QEMU from within gdb and establish the
connection via a pipe:
(gdb) target remote | exec qemu-system-i386 -gdb stdio ...
-s Shorthand for -gdb tcp::1234, i.e. open a gdbserver on TCP port 1234.
then boot the guest and when it is up, do
$ gdb ./vmlinux
$ target remote localhost:1234
and type in the prompt
$ (gdb) x/50i resched_task
It gives here:
(gdb) x/50i resched_task
0xffffffff810836f0 <resched_task>: data32 data32 data32 xchg %ax,%ax
0xffffffff810836f5 <resched_task+5>: push %rbp
0xffffffff810836f6 <resched_task+6>: mov 0x85e123(%rip),%r10d # 0xffffffff818e1820 <debug_locks>
0xffffffff810836fd <resched_task+13>: mov %rsp,%rbp
0xffffffff81083700 <resched_task+16>: push %r12
0xffffffff81083702 <resched_task+18>: test %r10d,%r10d
0xffffffff81083705 <resched_task+21>: push %rbx
0xffffffff81083706 <resched_task+22>: mov %rdi,%rbx
0xffffffff81083709 <resched_task+25>: jne 0xffffffff81083760 <resched_task+112>
0xffffffff8108370b <resched_task+27>: mov 0x8(%rbx),%rax
0xffffffff8108370f <resched_task+31>: mov 0x10(%rax),%rdx
0xffffffff81083713 <resched_task+35>: and $0x8,%edx
0xffffffff81083716 <resched_task+38>: jne 0xffffffff8108373c <resched_task+76>
0xffffffff81083718 <resched_task+40>: lock orb $0x8,0x10(%rax)
0xffffffff8108371d <resched_task+45>: mov 0x8(%rbx),%rax
0xffffffff81083721 <resched_task+49>: mov 0x18(%rax),%r12d
0xffffffff81083725 <resched_task+53>: callq 0xffffffff812d8fc0 <debug_smp_processor_id>
0xffffffff8108372a <resched_task+58>: cmp %r12d,%eax
0xffffffff8108372d <resched_task+61>: je 0xffffffff810837a0 <resched_task+176>
0xffffffff8108372f <resched_task+63>: mfence
^^^^^^
I want to make sure the smp_mb() is really replaced with an MFENCE there.
Thanks!
--
Regards/Gruss,
Boris.
Sent from a fat crate under my desk. Formatting is fine.
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