The current code uses a lot of casts to access the fields
member in struct synth_trace_events with different sizes.
This makes the code hard to read, and had already introduced
an endianness bug. Use a union and struct instead.
Signed-off-by: Sven Schnelle <[email protected]>
---
Changes in v2:
- cosmetic changes
- add struct trace_dynamic_info to include/linux/trace_events.h
include/linux/trace_events.h | 11 ++++
kernel/trace/trace.h | 10 ++++
kernel/trace/trace_events_synth.c | 87 +++++++++++++------------------
3 files changed, 58 insertions(+), 50 deletions(-)
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 3930e676436c..1e8bbdb8da90 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -59,6 +59,17 @@ int trace_raw_output_prep(struct trace_iterator *iter,
extern __printf(2, 3)
void trace_event_printf(struct trace_iterator *iter, const char *fmt, ...);
+/* Used to find the offset and length of dynamic fields in trace events */
+struct trace_dynamic_info {
+#ifdef CONFIG_CPU_BIG_ENDIAN
+ u16 offset;
+ u16 len;
+#else
+ u16 len;
+ u16 offset;
+#endif
+};
+
/*
* The trace entry - the most basic unit of tracing. This is what
* is printed in the end as a single line in the trace output, such as:
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index e1edc2197fc8..deca35c39bc9 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1295,6 +1295,16 @@ static inline void trace_branch_disable(void)
/* set ring buffers to default size if not already done so */
int tracing_update_buffers(void);
+struct trace_dynamic {
+ union {
+ u8 as_u8;
+ u16 as_u16;
+ u32 as_u32;
+ u64 as_u64;
+ struct trace_dynamic_info as_dynamic;
+ };
+};
+
struct ftrace_event_field {
struct list_head link;
const char *name;
diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index dd398afc8e25..57beba49c888 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -127,7 +127,7 @@ static bool synth_event_match(const char *system, const char *event,
struct synth_trace_event {
struct trace_entry ent;
- u64 fields[];
+ struct trace_dynamic fields[];
};
static int synth_event_define_fields(struct trace_event_call *call)
@@ -321,19 +321,19 @@ static const char *synth_field_fmt(char *type)
static void print_synth_event_num_val(struct trace_seq *s,
char *print_fmt, char *name,
- int size, u64 val, char *space)
+ int size, struct trace_dynamic *val, char *space)
{
switch (size) {
case 1:
- trace_seq_printf(s, print_fmt, name, (u8)val, space);
+ trace_seq_printf(s, print_fmt, name, val->as_u8, space);
break;
case 2:
- trace_seq_printf(s, print_fmt, name, (u16)val, space);
+ trace_seq_printf(s, print_fmt, name, val->as_u16, space);
break;
case 4:
- trace_seq_printf(s, print_fmt, name, (u32)val, space);
+ trace_seq_printf(s, print_fmt, name, val->as_u32, space);
break;
default:
@@ -374,36 +374,26 @@ static enum print_line_t print_synth_event(struct trace_iterator *iter,
/* parameter values */
if (se->fields[i]->is_string) {
if (se->fields[i]->is_dynamic) {
- u32 offset, data_offset;
- char *str_field;
-
- offset = (u32)entry->fields[n_u64];
- data_offset = offset & 0xffff;
-
- str_field = (char *)entry + data_offset;
+ struct trace_dynamic *data = &entry->fields[n_u64];
trace_seq_printf(s, print_fmt, se->fields[i]->name,
STR_VAR_LEN_MAX,
- str_field,
+ (char *)entry + data->as_dynamic.offset,
i == se->n_fields - 1 ? "" : " ");
n_u64++;
} else {
trace_seq_printf(s, print_fmt, se->fields[i]->name,
STR_VAR_LEN_MAX,
- (char *)&entry->fields[n_u64],
+ (char *)&entry->fields[n_u64].as_u64,
i == se->n_fields - 1 ? "" : " ");
n_u64 += STR_VAR_LEN_MAX / sizeof(u64);
}
} else if (se->fields[i]->is_stack) {
- u32 offset, data_offset, len;
unsigned long *p, *end;
+ struct trace_dynamic *data = &entry->fields[n_u64];
- offset = (u32)entry->fields[n_u64];
- data_offset = offset & 0xffff;
- len = offset >> 16;
-
- p = (void *)entry + data_offset;
- end = (void *)p + len - (sizeof(long) - 1);
+ p = (void *)entry + data->as_dynamic.offset;
+ end = (void *)p + data->as_dynamic.len - (sizeof(long) - 1);
trace_seq_printf(s, "%s=STACK:\n", se->fields[i]->name);
@@ -419,13 +409,13 @@ static enum print_line_t print_synth_event(struct trace_iterator *iter,
print_synth_event_num_val(s, print_fmt,
se->fields[i]->name,
se->fields[i]->size,
- entry->fields[n_u64],
+ &entry->fields[n_u64],
space);
if (strcmp(se->fields[i]->type, "gfp_t") == 0) {
trace_seq_puts(s, " (");
trace_print_flags_seq(s, "|",
- entry->fields[n_u64],
+ entry->fields[n_u64].as_u64,
__flags);
trace_seq_putc(s, ')');
}
@@ -454,21 +444,16 @@ static unsigned int trace_string(struct synth_trace_event *entry,
int ret;
if (is_dynamic) {
- u32 data_offset;
+ struct trace_dynamic *data = &entry->fields[*n_u64];
- data_offset = struct_size(entry, fields, event->n_u64);
- data_offset += data_size;
-
- len = fetch_store_strlen((unsigned long)str_val);
-
- data_offset |= len << 16;
- *(u32 *)&entry->fields[*n_u64] = data_offset;
+ data->as_dynamic.offset = struct_size(entry, fields, event->n_u64) + data_size;
+ data->as_dynamic.len = fetch_store_strlen((unsigned long)str_val);
ret = fetch_store_string((unsigned long)str_val, &entry->fields[*n_u64], entry);
(*n_u64)++;
} else {
- str_field = (char *)&entry->fields[*n_u64];
+ str_field = (char *)&entry->fields[*n_u64].as_u64;
#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
if ((unsigned long)str_val < TASK_SIZE)
@@ -492,6 +477,7 @@ static unsigned int trace_stack(struct synth_trace_event *entry,
unsigned int data_size,
unsigned int *n_u64)
{
+ struct trace_dynamic *data = &entry->fields[*n_u64];
unsigned int len;
u32 data_offset;
void *data_loc;
@@ -515,8 +501,9 @@ static unsigned int trace_stack(struct synth_trace_event *entry,
memcpy(data_loc, stack, len);
/* Fill in the field that holds the offset/len combo */
- data_offset |= len << 16;
- *(u32 *)&entry->fields[*n_u64] = data_offset;
+
+ data->as_dynamic.offset = data_offset;
+ data->as_dynamic.len = len;
(*n_u64)++;
@@ -592,19 +579,19 @@ static notrace void trace_event_raw_event_synth(void *__data,
switch (field->size) {
case 1:
- *(u8 *)&entry->fields[n_u64] = (u8)val;
+ entry->fields[n_u64].as_u8 = (u8)val;
break;
case 2:
- *(u16 *)&entry->fields[n_u64] = (u16)val;
+ entry->fields[n_u64].as_u16 = (u16)val;
break;
case 4:
- *(u32 *)&entry->fields[n_u64] = (u32)val;
+ entry->fields[n_u64].as_u32 = (u32)val;
break;
default:
- entry->fields[n_u64] = val;
+ entry->fields[n_u64].as_u64 = val;
break;
}
n_u64++;
@@ -1791,19 +1778,19 @@ int synth_event_trace(struct trace_event_file *file, unsigned int n_vals, ...)
switch (field->size) {
case 1:
- *(u8 *)&state.entry->fields[n_u64] = (u8)val;
+ state.entry->fields[n_u64].as_u8 = (u8)val;
break;
case 2:
- *(u16 *)&state.entry->fields[n_u64] = (u16)val;
+ state.entry->fields[n_u64].as_u16 = (u16)val;
break;
case 4:
- *(u32 *)&state.entry->fields[n_u64] = (u32)val;
+ state.entry->fields[n_u64].as_u32 = (u32)val;
break;
default:
- state.entry->fields[n_u64] = val;
+ state.entry->fields[n_u64].as_u64 = val;
break;
}
n_u64++;
@@ -1884,19 +1871,19 @@ int synth_event_trace_array(struct trace_event_file *file, u64 *vals,
switch (field->size) {
case 1:
- *(u8 *)&state.entry->fields[n_u64] = (u8)val;
+ state.entry->fields[n_u64].as_u8 = (u8)val;
break;
case 2:
- *(u16 *)&state.entry->fields[n_u64] = (u16)val;
+ state.entry->fields[n_u64].as_u16 = (u16)val;
break;
case 4:
- *(u32 *)&state.entry->fields[n_u64] = (u32)val;
+ state.entry->fields[n_u64].as_u32 = (u32)val;
break;
default:
- state.entry->fields[n_u64] = val;
+ state.entry->fields[n_u64].as_u64 = val;
break;
}
n_u64++;
@@ -2031,19 +2018,19 @@ static int __synth_event_add_val(const char *field_name, u64 val,
} else {
switch (field->size) {
case 1:
- *(u8 *)&trace_state->entry->fields[field->offset] = (u8)val;
+ trace_state->entry->fields[field->offset].as_u8 = (u8)val;
break;
case 2:
- *(u16 *)&trace_state->entry->fields[field->offset] = (u16)val;
+ trace_state->entry->fields[field->offset].as_u16 = (u16)val;
break;
case 4:
- *(u32 *)&trace_state->entry->fields[field->offset] = (u32)val;
+ trace_state->entry->fields[field->offset].as_u32 = (u32)val;
break;
default:
- trace_state->entry->fields[field->offset] = val;
+ trace_state->entry->fields[field->offset].as_u64 = val;
break;
}
}
--
2.39.2
On Wed, 9 Aug 2023 09:14:59 +0200
Sven Schnelle <[email protected]> wrote:
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -1295,6 +1295,16 @@ static inline void trace_branch_disable(void)
> /* set ring buffers to default size if not already done so */
> int tracing_update_buffers(void);
>
> +struct trace_dynamic {
> + union {
> + u8 as_u8;
> + u16 as_u16;
> + u32 as_u32;
> + u64 as_u64;
> + struct trace_dynamic_info as_dynamic;
> + };
> +};
> +
No need to create a structure around a single element union. Also, I would
like to name it for what it is for.
union trace_synth_field {
u8 as_u8;
u16 as_u16;
u32 as_u32;
u64 as_u64;
struct trace_dynamic_info as_dynamic;
};
Other than that, the patch looks good. Although I still need to test it.
-- Steve
From: Steven Rostedt
> Sent: 09 August 2023 13:55
> On Wed, 9 Aug 2023 09:14:59 +0200
> Sven Schnelle <[email protected]> wrote:
>
> > --- a/kernel/trace/trace.h
> > +++ b/kernel/trace/trace.h
> > @@ -1295,6 +1295,16 @@ static inline void trace_branch_disable(void)
> > /* set ring buffers to default size if not already done so */
> > int tracing_update_buffers(void);
> >
> > +struct trace_dynamic {
> > + union {
> > + u8 as_u8;
> > + u16 as_u16;
> > + u32 as_u32;
> > + u64 as_u64;
> > + struct trace_dynamic_info as_dynamic;
> > + };
> > +};
> > +
>
> No need to create a structure around a single element union. Also, I would
> like to name it for what it is for.
>
> union trace_synth_field {
> u8 as_u8;
> u16 as_u16;
> u32 as_u32;
> u64 as_u64;
> struct trace_dynamic_info as_dynamic;
> };
>
> Other than that, the patch looks good. Although I still need to test it.
I was wondering if you need the u8 and u16 members at all?
Can't the values just be treated as 32bit?
Both char and short aren't really 'proper' arithmetic types.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
On Mon, 14 Aug 2023 11:34:20 +0000
David Laight <[email protected]> wrote:
> > No need to create a structure around a single element union. Also, I would
> > like to name it for what it is for.
> >
> > union trace_synth_field {
> > u8 as_u8;
> > u16 as_u16;
> > u32 as_u32;
> > u64 as_u64;
> > struct trace_dynamic_info as_dynamic;
> > };
> >
> > Other than that, the patch looks good. Although I still need to test it.
>
> I was wondering if you need the u8 and u16 members at all?
> Can't the values just be treated as 32bit?
> Both char and short aren't really 'proper' arithmetic types.
Not sure what you mean by "arithmatic types".
If you do something like:
~# echo 's:skb u16 protocol; u64 delta;' >> /sys/kernel/tracing/dynamic_events
~# echo 'hist:keys=skbaddr:ts=common_timestamp.usecs' >> /sys/kernel/tracing/events/net/netif_receive_skb/trigger
~# echo 'hist:keys=skbaddr:delta=common_timestamp.usecs-$ts:onmatch(net.netif_receive_skb).trace(skb,protocol,$delta)' >> /sys/kernel/tracing/events/skb/kfree_skb/trigger
Where it records the protocol as u16, I'm guessing that if we didn't use
this union, it might break on BIG_ENDIAN machines.
For reference, the kfree_skb event looks like:
system: skb
name: kfree_skb
ID: 1735
format:
field:unsigned short common_type; offset:0; size:2; signed:0;
field:unsigned char common_flags; offset:2; size:1; signed:0;
field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
field:int common_pid; offset:4; size:4; signed:1;
field:void * skbaddr; offset:8; size:8; signed:0;
field:void * location; offset:16; size:8; signed:0;
field:unsigned short protocol; offset:24; size:2; signed:0;
field:enum skb_drop_reason reason; offset:28; size:4; signed:0;
-- Steve