Messages in this thread | | | Subject | Re: [PATCH 1/3] powerpc: Emulation support for load/store instructions on LE | From | Ravi Bangoria <> | Date | Mon, 7 Nov 2016 00:29:04 +0530 |
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On Sunday 06 November 2016 01:01 AM, Anton Blanchard wrote: > Hi, > >> kprobe, uprobe, hw-breakpoint and xmon are the only user of >> emulate_step. >> >> Kprobe / uprobe single-steps instruction if they can't emulate it, so >> there is no problem with them. As I mention, hw-breakpoint is broken. >> However I'm not sure about xmon, I need to check that. > I was mostly concerned that it would impact kprobes. Sounds like we are > ok there. > >> So yes, there is no user-visible feature that depends on this. > Aren't hardware breakpoints exposed via perf? I'd call perf > user-visible.
Thanks Anton, That's a good catch. I tried this on ppc64le:
$ sudo cat /proc/kallsyms | grep pid_max c00000000116998c D pid_max
$ sudo ./perf record -a --event=mem:0xc00000000116998c sleep 10
Before patch: It does not record any data and throws below warning.
$ dmesg [ 817.895573] Unable to handle hardware breakpoint. Breakpoint at 0xc00000000116998c will be disabled. [ 817.895581] ------------[ cut here ]------------ [ 817.895588] WARNING: CPU: 24 PID: 2032 at arch/powerpc/kernel/hw_breakpoint.c:277 hw_breakpoint_handler+0x124/0x230 ...
After patch: It records data properly.
$ sudo ./perf report --stdio ... # Samples: 36 of event 'mem:0xc00000000116998c' # Event count (approx.): 36 # # Overhead Command Shared Object Symbol # ........ ............. ................ ............. # 63.89% kdumpctl [kernel.vmlinux] [k] alloc_pid 27.78% opal_errd [kernel.vmlinux] [k] alloc_pid 5.56% kworker/u97:4 [kernel.vmlinux] [k] alloc_pid 2.78% systemd [kernel.vmlinux] [k] alloc_pid
-Ravi
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