On 7/14/2026 5:14 PM, Steven Rostedt wrote:
> On Wed, 15 Jul 2026 02:32:06 +0800
> Jinchao Wang <[email protected]> wrote:
>
>> --- /dev/null
>> +++ b/include/trace/events/kwatch.h
>> @@ -0,0 +1,57 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +#undef TRACE_SYSTEM
>> +#define TRACE_SYSTEM kwatch
>> +
>> +#if !defined(_TRACE_KWATCH_H) || defined(TRACE_HEADER_MULTI_READ)
>> +#define _TRACE_KWATCH_H
>> +
>> +#include <linux/tracepoint.h>
>> +#include <linux/ptrace.h>
>> +
>> +#define KWATCH_STACK_DEPTH 8
>> +
>> +struct trace_seq;
>> +const char *kwatch_trace_print_stack(struct trace_seq *p,
>> + const unsigned long *stack,
>> + unsigned int nr);
>> +
>> +TRACE_EVENT(kwatch_hit,
>> + TP_PROTO(unsigned long ip, unsigned long sp, unsigned long addr,
>> + u64 time_ns,
>> + unsigned long *stack_entries, unsigned int stack_nr),
>> + TP_ARGS(ip, sp, addr, time_ns, stack_entries, stack_nr),
>> +
>> + TP_STRUCT__entry(
>> + __field(unsigned long, ip)
>> + __field(unsigned long, sp)
>> + __field(unsigned long, addr)
>> + __field(u64, time_ns)
>
> Move the time_ns to the first field, as unsigned long on 32 bit
> architectures is 4 bytes, and this will make 4 byte "hole" in the event.
Will fix in v2.>
>
>> + __field(unsigned int, stack_nr)
>
> Make stack_nr the last element for the same reason.
Will fix in v2.
>
>> + __array(unsigned long, stack, KWATCH_STACK_DEPTH)
>
> Make the above a dynamic array based on stack entries.
>
> __dynamic_array(unsigned long, stack, min_t(unsigned int,
> stack_nr,
> KWATCH_STACK_DEPTH);
Much better than always paying for the full depth - will convert to
__dynamic_array (and use __get_dynamic_array() in TP_fast_assign and
TP_printk as you showed) in v2.
Thank you for the review!
Thanks,
Jinchao
>
>
>> + ),
>> +
>> + TP_fast_assign(
>> + unsigned int i;
> unsigned long *stack = __get_dynamic_array(stack);
>> +
>> + __entry->ip = ip;
>> + __entry->sp = sp;
>> + __entry->addr = addr;
>> + __entry->time_ns = time_ns;
>> + __entry->stack_nr = min_t(unsigned int, stack_nr,
>> + KWATCH_STACK_DEPTH);
>> + for (i = 0; i < __entry->stack_nr; i++)
>> + __entry->stack[i] = stack_entries[i];
>
> stack[i] = stack_entries[i];
>
>> + ),
>> +
>> + TP_printk("KWatch HIT: time=%llu.%06lu ip=%pS addr=0x%lx%s",
>> + __entry->time_ns / 1000000000ULL,
>> + (unsigned long)((__entry->time_ns / 1000ULL) % 1000000ULL),
>> + (void *)__entry->ip, __entry->addr,
>> + kwatch_trace_print_stack(p, __entry->stack,
>
> kwatch_trace_print_stack(p, __get_dynamic_array(stack),
>
>> + __entry->stack_nr))
>> +);
>> +
>
> -- Steve
