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Subject: Re: [PATCH v4 2/2] kernel/trace: Provide default impelentations
 defined in trace_probe_tmpl.h
To:     "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc:     rostedt@goodmis.org, arnd@arndb.de, linux-kernel@vger.kernel.org,
        linux-trace-kernel@vger.kernel.org, linux-arch@vger.kernel.org
References: <1672211305-31482-1-git-send-email-chensong_2000@189.cn>
 <20221229183027.6f2c75ba0b2924a2bfd0499d@kernel.org>
Content-Language: en-US
From:   Song Chen <chensong_2000@189.cn>
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Hi,

在 2022/12/29 17:30, Masami Hiramatsu (Google) 写道:
> On Wed, 28 Dec 2022 15:08:25 +0800
> Song Chen <chensong_2000@189.cn> wrote:
> 
>> There are 7 function definitions in trace_probe_tmpl.h, they are:
>>
>> 1, process_fetch_insn
> 
> Other functions except for this are OK for me.
> But I think this function should have different instance for kprobe
> and eprobe, because the passed 'void *rec' is completely different.
> For the kprobe's process_fetch_insn() will take a 'pt_regs *', on the
> other hand, the eprobe's process_fetch_insn() will take a
> 'ftrace_event_field *'.
> I also, don't want to expose get_event_field() function because
> it is only for the eprobes.
> 
> What about making a new common function and call it in default case
> from both process_fetch_insn()? Your goal is reducing the redundant
> code, then it is enough to share only the common code. :)
> 
> For example, in trace_probe_kernel.h,
> 
> process_common_fetch_insn(struct fetch_insn *code, void *dest, void *base, unsigned long *val)
> {
> 	switch (code->op) {
> 	case FETCH_OP_IMM:
> 		*val = code->immediate;
> 		break;
> 	case FETCH_OP_COMM:
> 		*val = (unsigned long)current->comm;
> 		break;
> 	case FETCH_OP_DATA:
> 		*val = (unsigned long)code->data;
> 		break;
> 	default:
> 		return -EILSEQ;
> 	}
> 	return 0;
> }
> 
> For kprobe events:
> 
> process_fetch_insn(struct fetch_insn *code, void *rec, void *dest, void *base)
> {
> 	while (code->op == FETCH_NOP_SYMBOL)
> 		code++;
> 	switch (code->op) {
> 	case FETCH_OP_REG:
> 		val = regs_get_register(regs, code->param);
> 		...
> 	default:
> 		ret = process_common_fetch_insn(code, dest, base, &val);
> 		if (ret < 0)
> 			return ret;
> 	}
> 	...
> }
> 
> For eprobe events:
> 
> process_fetch_insn(struct fetch_insn *code, void *rec, void *dest, void *base)
> {
> 	while (code->op == FETCH_NOP_SYMBOL)
> 		code++;
> 	if (code->op == FETCH_OP_TP_ARG) {
> 		val = get_event_field(code, rec);
> 	} else {
> 		ret = process_common_fetch_insn(code, dest, base, &val);
> 		if (ret < 0)
> 			return ret;
> 	}
> 	...
> }
> 
> You also don't see the error related to CONFIG_HAVE_REGS_AND_STACK_ACCESS_API. :)
> 
> Thank you,
> 

Thanks a lot for the good idea and so specific demo code, i accept it 
and will submit a new one based on it.

If we think about it further, we can implement process_common_fetch_insn 
in trace_probe_tmpl.h, uprobe can benefit from it as well, what do you 
think? i will include it in the next submit and you can have a look.

Thanks again.

Song

>> 2, fetch_store_strlen
>> 3, fetch_store_string
>> 4, fetch_store_strlen_user
>> 5, fetch_store_string_user
>> 6, probe_mem_read
>> 7, probe_mem_read_user
>>
>> Every C file which includes trace_probe_tmpl.h has to implement them,
>> otherwise it gets warnings and errors. However, some of them are identical,
>> like kprobe and eprobe, as a result, there is a lot redundant code in those
>> 2 files.
>>
>> This patch would like to provide default behaviors for those functions
>> which kprobe and eprobe can share by just including trace_probe_kernel.h
>> with trace_probe_tmpl.h together.
>>
>> It removes redundant code, increases readability, and more importantly,
>> makes it easier to introduce a new feature based on trace probe
>> (it's possible).
>>
>> Signed-off-by: Song Chen <chensong_2000@189.cn>
>> Reported-by: kernel test robot <lkp@intel.com>
>>
>> ---
>> v2:
>> 1, reorganize patchset
>>
>> v3:
>> 1, mark nokprobe_inline for get_event_field
>> 2, remove warnings reported from kernel test robot
>> 3, fix errors reported from kernel test robot
>>
>> v4:
>> 1, reset changes in v3(2) and v3(3), they are not reasonable fix.
>> 2, I intended to introduce a new header file to exclude
>> trace_events_synth.c out of the patch. However, after looking
>> further, i found the errors in [1] are introduced by this patch,
>> but the warning in [1] are not. The errors can be fixed by adding
>> "#ifdef CONFIG_HAVE_REGS_AND_STACK_ACCESS_API".
>>
>> [1]:https://lore.kernel.org/lkml/202211301946.pkLE4PDp-lkp@intel.com/
>> ---
>>   kernel/trace/trace_eprobe.c       | 144 ------------------------------
>>   kernel/trace/trace_events_synth.c |   7 +-
>>   kernel/trace/trace_kprobe.c       | 102 ---------------------
>>   kernel/trace/trace_probe_kernel.h | 143 +++++++++++++++++++++++++++--
>>   4 files changed, 141 insertions(+), 255 deletions(-)
>>
>> diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
>> index bdb26eee7a0c..60ced4a7a25d 100644
>> --- a/kernel/trace/trace_eprobe.c
>> +++ b/kernel/trace/trace_eprobe.c
>> @@ -319,64 +319,6 @@ print_eprobe_event(struct trace_iterator *iter, int flags,
>>   	return trace_handle_return(s);
>>   }
>>   
>> -static unsigned long get_event_field(struct fetch_insn *code, void *rec)
>> -{
>> -	struct ftrace_event_field *field = code->data;
>> -	unsigned long val;
>> -	void *addr;
>> -
>> -	addr = rec + field->offset;
>> -
>> -	if (is_string_field(field)) {
>> -		switch (field->filter_type) {
>> -		case FILTER_DYN_STRING:
>> -			val = (unsigned long)(rec + (*(unsigned int *)addr & 0xffff));
>> -			break;
>> -		case FILTER_RDYN_STRING:
>> -			val = (unsigned long)(addr + (*(unsigned int *)addr & 0xffff));
>> -			break;
>> -		case FILTER_STATIC_STRING:
>> -			val = (unsigned long)addr;
>> -			break;
>> -		case FILTER_PTR_STRING:
>> -			val = (unsigned long)(*(char *)addr);
>> -			break;
>> -		default:
>> -			WARN_ON_ONCE(1);
>> -			return 0;
>> -		}
>> -		return val;
>> -	}
>> -
>> -	switch (field->size) {
>> -	case 1:
>> -		if (field->is_signed)
>> -			val = *(char *)addr;
>> -		else
>> -			val = *(unsigned char *)addr;
>> -		break;
>> -	case 2:
>> -		if (field->is_signed)
>> -			val = *(short *)addr;
>> -		else
>> -			val = *(unsigned short *)addr;
>> -		break;
>> -	case 4:
>> -		if (field->is_signed)
>> -			val = *(int *)addr;
>> -		else
>> -			val = *(unsigned int *)addr;
>> -		break;
>> -	default:
>> -		if (field->is_signed)
>> -			val = *(long *)addr;
>> -		else
>> -			val = *(unsigned long *)addr;
>> -		break;
>> -	}
>> -	return val;
>> -}
>> -
>>   static int get_eprobe_size(struct trace_probe *tp, void *rec)
>>   {
>>   	struct fetch_insn *code;
>> @@ -419,92 +361,6 @@ static int get_eprobe_size(struct trace_probe *tp, void *rec)
>>   	return ret;
>>   }
>>   
>> -/* Kprobe specific fetch functions */
>> -
>> -/* Note that we don't verify it, since the code does not come from user space */
>> -static int
>> -process_fetch_insn(struct fetch_insn *code, void *rec, void *dest,
>> -		   void *base)
>> -{
>> -	unsigned long val;
>> -
>> - retry:
>> -	switch (code->op) {
>> -	case FETCH_OP_TP_ARG:
>> -		val = get_event_field(code, rec);
>> -		break;
>> -	case FETCH_OP_IMM:
>> -		val = code->immediate;
>> -		break;
>> -	case FETCH_OP_COMM:
>> -		val = (unsigned long)current->comm;
>> -		break;
>> -	case FETCH_OP_DATA:
>> -		val = (unsigned long)code->data;
>> -		break;
>> -	case FETCH_NOP_SYMBOL:	/* Ignore a place holder */
>> -		code++;
>> -		goto retry;
>> -	default:
>> -		return -EILSEQ;
>> -	}
>> -	code++;
>> -	return process_fetch_insn_bottom(code, val, dest, base);
>> -}
>> -NOKPROBE_SYMBOL(process_fetch_insn)
>> -
>> -/* Return the length of string -- including null terminal byte */
>> -static nokprobe_inline int
>> -fetch_store_strlen_user(unsigned long addr)
>> -{
>> -	return kern_fetch_store_strlen_user(addr);
>> -}
>> -
>> -/* Return the length of string -- including null terminal byte */
>> -static nokprobe_inline int
>> -fetch_store_strlen(unsigned long addr)
>> -{
>> -	return kern_fetch_store_strlen(addr);
>> -}
>> -
>> -/*
>> - * Fetch a null-terminated string from user. Caller MUST set *(u32 *)buf
>> - * with max length and relative data location.
>> - */
>> -static nokprobe_inline int
>> -fetch_store_string_user(unsigned long addr, void *dest, void *base)
>> -{
>> -	return kern_fetch_store_string_user(addr, dest, base);
>> -}
>> -
>> -/*
>> - * Fetch a null-terminated string. Caller MUST set *(u32 *)buf with max
>> - * length and relative data location.
>> - */
>> -static nokprobe_inline int
>> -fetch_store_string(unsigned long addr, void *dest, void *base)
>> -{
>> -	return kern_fetch_store_string(addr, dest, base);
>> -}
>> -
>> -static nokprobe_inline int
>> -probe_mem_read_user(void *dest, void *src, size_t size)
>> -{
>> -	const void __user *uaddr =  (__force const void __user *)src;
>> -
>> -	return copy_from_user_nofault(dest, uaddr, size);
>> -}
>> -
>> -static nokprobe_inline int
>> -probe_mem_read(void *dest, void *src, size_t size)
>> -{
>> -#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
>> -	if ((unsigned long)src < TASK_SIZE)
>> -		return probe_mem_read_user(dest, src, size);
>> -#endif
>> -	return copy_from_kernel_nofault(dest, src, size);
>> -}
>> -
>>   /* eprobe handler */
>>   static inline void
>>   __eprobe_trace_func(struct eprobe_data *edata, void *rec)
>> diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
>> index e310052dc83c..7460f18ba973 100644
>> --- a/kernel/trace/trace_events_synth.c
>> +++ b/kernel/trace/trace_events_synth.c
>> @@ -18,6 +18,7 @@
>>   #include <linux/trace_events.h>
>>   #include <trace/events/mmflags.h>
>>   #include "trace_probe.h"
>> +#include "trace_probe_tmpl.h"
>>   #include "trace_probe_kernel.h"
>>   
>>   #include "trace_synth.h"
>> @@ -420,12 +421,12 @@ static unsigned int trace_string(struct synth_trace_event *entry,
>>   		data_offset += event->n_u64 * sizeof(u64);
>>   		data_offset += data_size;
>>   
>> -		len = kern_fetch_store_strlen((unsigned long)str_val);
>> +		len = fetch_store_strlen((unsigned long)str_val);
>>   
>>   		data_offset |= len << 16;
>>   		*(u32 *)&entry->fields[*n_u64] = data_offset;
>>   
>> -		ret = kern_fetch_store_string((unsigned long)str_val, &entry->fields[*n_u64], entry);
>> +		ret = fetch_store_string((unsigned long)str_val, &entry->fields[*n_u64], entry);
>>   
>>   		(*n_u64)++;
>>   	} else {
>> @@ -473,7 +474,7 @@ static notrace void trace_event_raw_event_synth(void *__data,
>>   		val_idx = var_ref_idx[field_pos];
>>   		str_val = (char *)(long)var_ref_vals[val_idx];
>>   
>> -		len = kern_fetch_store_strlen((unsigned long)str_val);
>> +		len = fetch_store_strlen((unsigned long)str_val);
>>   
>>   		fields_size += len;
>>   	}
>> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
>> index a4ffa864dbb7..c2e0b741ae82 100644
>> --- a/kernel/trace/trace_kprobe.c
>> +++ b/kernel/trace/trace_kprobe.c
>> @@ -1218,108 +1218,6 @@ static const struct file_operations kprobe_profile_ops = {
>>   	.release        = seq_release,
>>   };
>>   
>> -/* Kprobe specific fetch functions */
>> -
>> -/* Return the length of string -- including null terminal byte */
>> -static nokprobe_inline int
>> -fetch_store_strlen_user(unsigned long addr)
>> -{
>> -	return kern_fetch_store_strlen_user(addr);
>> -}
>> -
>> -/* Return the length of string -- including null terminal byte */
>> -static nokprobe_inline int
>> -fetch_store_strlen(unsigned long addr)
>> -{
>> -	return kern_fetch_store_strlen(addr);
>> -}
>> -
>> -/*
>> - * Fetch a null-terminated string from user. Caller MUST set *(u32 *)buf
>> - * with max length and relative data location.
>> - */
>> -static nokprobe_inline int
>> -fetch_store_string_user(unsigned long addr, void *dest, void *base)
>> -{
>> -	return kern_fetch_store_string_user(addr, dest, base);
>> -}
>> -
>> -/*
>> - * Fetch a null-terminated string. Caller MUST set *(u32 *)buf with max
>> - * length and relative data location.
>> - */
>> -static nokprobe_inline int
>> -fetch_store_string(unsigned long addr, void *dest, void *base)
>> -{
>> -	return kern_fetch_store_string(addr, dest, base);
>> -}
>> -
>> -static nokprobe_inline int
>> -probe_mem_read_user(void *dest, void *src, size_t size)
>> -{
>> -	const void __user *uaddr =  (__force const void __user *)src;
>> -
>> -	return copy_from_user_nofault(dest, uaddr, size);
>> -}
>> -
>> -static nokprobe_inline int
>> -probe_mem_read(void *dest, void *src, size_t size)
>> -{
>> -#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
>> -	if ((unsigned long)src < TASK_SIZE)
>> -		return probe_mem_read_user(dest, src, size);
>> -#endif
>> -	return copy_from_kernel_nofault(dest, src, size);
>> -}
>> -
>> -/* Note that we don't verify it, since the code does not come from user space */
>> -static int
>> -process_fetch_insn(struct fetch_insn *code, void *rec, void *dest,
>> -		   void *base)
>> -{
>> -	struct pt_regs *regs = rec;
>> -	unsigned long val;
>> -
>> -retry:
>> -	/* 1st stage: get value from context */
>> -	switch (code->op) {
>> -	case FETCH_OP_REG:
>> -		val = regs_get_register(regs, code->param);
>> -		break;
>> -	case FETCH_OP_STACK:
>> -		val = regs_get_kernel_stack_nth(regs, code->param);
>> -		break;
>> -	case FETCH_OP_STACKP:
>> -		val = kernel_stack_pointer(regs);
>> -		break;
>> -	case FETCH_OP_RETVAL:
>> -		val = regs_return_value(regs);
>> -		break;
>> -	case FETCH_OP_IMM:
>> -		val = code->immediate;
>> -		break;
>> -	case FETCH_OP_COMM:
>> -		val = (unsigned long)current->comm;
>> -		break;
>> -	case FETCH_OP_DATA:
>> -		val = (unsigned long)code->data;
>> -		break;
>> -#ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
>> -	case FETCH_OP_ARG:
>> -		val = regs_get_kernel_argument(regs, code->param);
>> -		break;
>> -#endif
>> -	case FETCH_NOP_SYMBOL:	/* Ignore a place holder */
>> -		code++;
>> -		goto retry;
>> -	default:
>> -		return -EILSEQ;
>> -	}
>> -	code++;
>> -
>> -	return process_fetch_insn_bottom(code, val, dest, base);
>> -}
>> -NOKPROBE_SYMBOL(process_fetch_insn)
>>   
>>   /* Kprobe handler */
>>   static nokprobe_inline void
>> diff --git a/kernel/trace/trace_probe_kernel.h b/kernel/trace/trace_probe_kernel.h
>> index 77dbd9ff9782..39f44513ec4e 100644
>> --- a/kernel/trace/trace_probe_kernel.h
>> +++ b/kernel/trace/trace_probe_kernel.h
>> @@ -12,7 +12,7 @@
>>    */
>>   /* Return the length of string -- including null terminal byte */
>>   static nokprobe_inline int
>> -kern_fetch_store_strlen_user(unsigned long addr)
>> +fetch_store_strlen_user(unsigned long addr)
>>   {
>>   	const void __user *uaddr =  (__force const void __user *)addr;
>>   	int ret;
>> @@ -29,14 +29,14 @@ kern_fetch_store_strlen_user(unsigned long addr)
>>   
>>   /* Return the length of string -- including null terminal byte */
>>   static nokprobe_inline int
>> -kern_fetch_store_strlen(unsigned long addr)
>> +fetch_store_strlen(unsigned long addr)
>>   {
>>   	int ret, len = 0;
>>   	u8 c;
>>   
>>   #ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
>>   	if (addr < TASK_SIZE)
>> -		return kern_fetch_store_strlen_user(addr);
>> +		return fetch_store_strlen_user(addr);
>>   #endif
>>   
>>   	do {
>> @@ -63,7 +63,7 @@ static nokprobe_inline void set_data_loc(int ret, void *dest, void *__dest, void
>>    * with max length and relative data location.
>>    */
>>   static nokprobe_inline int
>> -kern_fetch_store_string_user(unsigned long addr, void *dest, void *base)
>> +fetch_store_string_user(unsigned long addr, void *dest, void *base)
>>   {
>>   	const void __user *uaddr =  (__force const void __user *)addr;
>>   	int maxlen = get_loc_len(*(u32 *)dest);
>> @@ -86,7 +86,7 @@ kern_fetch_store_string_user(unsigned long addr, void *dest, void *base)
>>    * length and relative data location.
>>    */
>>   static nokprobe_inline int
>> -kern_fetch_store_string(unsigned long addr, void *dest, void *base)
>> +fetch_store_string(unsigned long addr, void *dest, void *base)
>>   {
>>   	int maxlen = get_loc_len(*(u32 *)dest);
>>   	void *__dest;
>> @@ -94,7 +94,7 @@ kern_fetch_store_string(unsigned long addr, void *dest, void *base)
>>   
>>   #ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
>>   	if ((unsigned long)addr < TASK_SIZE)
>> -		return kern_fetch_store_string_user(addr, dest, base);
>> +		return fetch_store_string_user(addr, dest, base);
>>   #endif
>>   
>>   	if (unlikely(!maxlen))
>> @@ -112,4 +112,135 @@ kern_fetch_store_string(unsigned long addr, void *dest, void *base)
>>   	return ret;
>>   }
>>   
>> +static nokprobe_inline int
>> +probe_mem_read_user(void *dest, void *src, size_t size)
>> +{
>> +	const void __user *uaddr =  (__force const void __user *)src;
>> +
>> +	return copy_from_user_nofault(dest, uaddr, size);
>> +}
>> +
>> +static nokprobe_inline int
>> +probe_mem_read(void *dest, void *src, size_t size)
>> +{
>> +#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
>> +	if ((unsigned long)src < TASK_SIZE)
>> +		return probe_mem_read_user(dest, src, size);
>> +#endif
>> +	return copy_from_kernel_nofault(dest, src, size);
>> +}
>> +
>> +static nokprobe_inline unsigned long
>> +get_event_field(struct fetch_insn *code, void *rec)
>> +{
>> +	struct ftrace_event_field *field = code->data;
>> +	unsigned long val;
>> +	void *addr;
>> +
>> +	addr = rec + field->offset;
>> +
>> +	if (is_string_field(field)) {
>> +		switch (field->filter_type) {
>> +		case FILTER_DYN_STRING:
>> +			val = (unsigned long)(rec + (*(unsigned int *)addr & 0xffff));
>> +			break;
>> +		case FILTER_RDYN_STRING:
>> +			val = (unsigned long)(addr + (*(unsigned int *)addr & 0xffff));
>> +			break;
>> +		case FILTER_STATIC_STRING:
>> +			val = (unsigned long)addr;
>> +			break;
>> +		case FILTER_PTR_STRING:
>> +			val = (unsigned long)(*(char *)addr);
>> +			break;
>> +		default:
>> +			WARN_ON_ONCE(1);
>> +			return 0;
>> +		}
>> +		return val;
>> +	}
>> +
>> +	switch (field->size) {
>> +	case 1:
>> +		if (field->is_signed)
>> +			val = *(char *)addr;
>> +		else
>> +			val = *(unsigned char *)addr;
>> +		break;
>> +	case 2:
>> +		if (field->is_signed)
>> +			val = *(short *)addr;
>> +		else
>> +			val = *(unsigned short *)addr;
>> +		break;
>> +	case 4:
>> +		if (field->is_signed)
>> +			val = *(int *)addr;
>> +		else
>> +			val = *(unsigned int *)addr;
>> +		break;
>> +	default:
>> +		if (field->is_signed)
>> +			val = *(long *)addr;
>> +		else
>> +			val = *(unsigned long *)addr;
>> +		break;
>> +	}
>> +	return val;
>> +}
>> +
>> +/* Note that we don't verify it, since the code does not come from user space */
>> +static int
>> +process_fetch_insn(struct fetch_insn *code, void *rec, void *dest,
>> +		   void *base)
>> +{
>> +	struct pt_regs *regs = rec;
>> +	unsigned long val;
>> +
>> +retry:
>> +	/* 1st stage: get value from context */
>> +	switch (code->op) {
>> +#ifdef CONFIG_HAVE_REGS_AND_STACK_ACCESS_API
>> +	case FETCH_OP_REG:
>> +		val = regs_get_register(regs, code->param);
>> +		break;
>> +	case FETCH_OP_STACK:
>> +		val = regs_get_kernel_stack_nth(regs, code->param);
>> +		break;
>> +	case FETCH_OP_STACKP:
>> +		val = kernel_stack_pointer(regs);
>> +		break;
>> +	case FETCH_OP_RETVAL:
>> +		val = regs_return_value(regs);
>> +		break;
>> +#endif
>> +	case FETCH_OP_IMM:
>> +		val = code->immediate;
>> +		break;
>> +	case FETCH_OP_COMM:
>> +		val = (unsigned long)current->comm;
>> +		break;
>> +	case FETCH_OP_DATA:
>> +		val = (unsigned long)code->data;
>> +		break;
>> +#ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
>> +	case FETCH_OP_ARG:
>> +		val = regs_get_kernel_argument(regs, code->param);
>> +		break;
>> +#endif
>> +	case FETCH_NOP_SYMBOL:	/* Ignore a place holder */
>> +		code++;
>> +		goto retry;
>> +	case FETCH_OP_TP_ARG:
>> +		val = get_event_field(code, rec);
>> +		break;
>> +	default:
>> +		return -EILSEQ;
>> +	}
>> +	code++;
>> +
>> +	return process_fetch_insn_bottom(code, val, dest, base);
>> +}
>> +NOKPROBE_SYMBOL(process_fetch_insn)
>> +
>>   #endif /* __TRACE_PROBE_KERNEL_H_ */
>> -- 
>> 2.25.1
>>
> 
>