On Wed, Nov 27, 2019 at 11:01:23AM +0300, Alexey Brodkin wrote:
> 8-letter strings representing ARC perf events are stores in two
> 32-bit registers as ASCII characters like that: "IJMP", "IALL", "IJMPTAK" etc.
>
> And the same order of bytes in the word is used regardless CPU endianness.
>
> Which means in case of big-endian CPU core we need to swap bytes to get
> the same order as if it was on little-endian CPU.
>
> Otherwise we're seeing the following error message on boot:
> ------------------------->8----------------------
> ARC perf : 8 counters (32 bits), 40 conditions, [overflow IRQ support]
> sysfs: cannot create duplicate filename '/devices/arc_pct/events/pmji'
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.2.18 #3
> Stack Trace:
> arc_unwind_core+0xd4/0xfc
> dump_stack+0x64/0x80
> sysfs_warn_dup+0x46/0x58
> sysfs_add_file_mode_ns+0xb2/0x168
> create_files+0x70/0x2a0
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 1 at kernel/events/core.c:12144 perf_event_sysfs_init+0x70/0xa0
> Failed to register pmu: arc_pct, reason -17
> Modules linked in:
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.2.18 #3
> Stack Trace:
> arc_unwind_core+0xd4/0xfc
> dump_stack+0x64/0x80
> __warn+0x9c/0xd4
> warn_slowpath_fmt+0x22/0x2c
> perf_event_sysfs_init+0x70/0xa0
> ---[ end trace a75fb9a9837bd1ec ]---
> ------------------------->8----------------------
>
> What happens here we're trying to register more than one raw perf event
> with the same name "PMJI". Why? Because ARC perf events are 4 to 8 letters
> and encoded into two 32-bit words. In this particular case we deal with 2
> events:
> * "IJMP____" which counts all jump & branch instructions
> * "IJMPC___" which counts only conditional jumps & branches
>
> Those strings are split in two 32-bit words this way "IJMP" + "____" &
> "IJMP" + "C___" correspondingly. Now if we read them swapped due to CPU core
> being big-endian then we read "PMJI" + "____" & "PMJI" + "___C".
>
> And since we interpret read array of ASCII letters as a null-terminated string
> on big-endian CPU we end up with 2 events of the same name "PMJI".
>
> Signed-off-by: Alexey Brodkin <abrodkin@xxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
>
> Greg, Sasha, this is the same patch as
> commit 5effc09c4907 ("ARC: perf: Accommodate big-endian CPU")
> but fine-tuned to be applicable to kernels 4.19 and older.
Thanks, now queued up.
greg k-h
