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 introduced an endianness
bug. Use a union and struct instead.
Signed-off-by: Sven Schnelle <[email protected]>
---
kernel/trace/trace.h | 18 +++++++
kernel/trace/trace_events_synth.c | 87 +++++++++++++------------------
2 files changed, 55 insertions(+), 50 deletions(-)
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index e1edc2197fc8..8ff1c193eadb 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1295,6 +1295,24 @@ 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 {
+#ifdef CONFIG_CPU_BIG_ENDIAN
+ u16 offset;
+ u16 len;
+#else
+ u16 len;
+ u16 offset;
+#endif
+ };
+ };
+};
+
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..2760604f471f 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->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->offset;
+ end = (void *)p + data->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->offset = struct_size(entry, fields, event->n_u64) + data_size;
+ data->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->offset = data_offset;
+ data->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
Steven Rostedt <[email protected]> writes:
> The "dynamic" I was using wasn't about the fields were dynamic (union), but
> because the field the offset/len combo represents is of dynamic size. It's
> used all over the trace_events code.
>
> I would have in include/linux/trace_events.h (right above struct trace_entry):
>
> /* 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
> };
>
> And then it kernel/trace/trace.h:
>
> union trace_synthetic_field {
> u8 as_u8;
> u16 as_u16;
> u32 as_u32;
> u64 as_u64;
> struct trace_dynamic_info as_dynamic;
> };
Ok.
> I could work on the part of the trace_dynamic_info if you want.
Whatever you prefer. Should i update my patch and send it again, or do
you want to adjust it?
Thanks
Sven
On Tue, 8 Aug 2023 16:21:48 +0200
Sven Schnelle <[email protected]> wrote:
> +struct trace_dynamic {
> + union {
> + u8 as_u8;
> + u16 as_u16;
> + u32 as_u32;
> + u64 as_u64;
> + struct {
> +#ifdef CONFIG_CPU_BIG_ENDIAN
> + u16 offset;
> + u16 len;
> +#else
> + u16 len;
> + u16 offset;
> +#endif
> + };
> + };
> +};
> +
The "dynamic" I was using wasn't about the fields were dynamic (union), but
because the field the offset/len combo represents is of dynamic size. It's
used all over the trace_events code.
I would have in include/linux/trace_events.h (right above struct trace_entry):
/* 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
};
And then it kernel/trace/trace.h:
union trace_synthetic_field {
u8 as_u8;
u16 as_u16;
u32 as_u32;
u64 as_u64;
struct trace_dynamic_info as_dynamic;
};
I could work on the part of the trace_dynamic_info if you want.
-- Steve
On Tue, 08 Aug 2023 19:33:06 +0200
Sven Schnelle <[email protected]> wrote:
> Steven Rostedt <[email protected]> writes:
>
> > The "dynamic" I was using wasn't about the fields were dynamic (union), but
> > because the field the offset/len combo represents is of dynamic size. It's
> > used all over the trace_events code.
> >
> > I would have in include/linux/trace_events.h (right above struct trace_entry):
> >
> > /* 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
> > };
> >
> > And then it kernel/trace/trace.h:
> >
> > union trace_synthetic_field {
> > u8 as_u8;
> > u16 as_u16;
> > u32 as_u32;
> > u64 as_u64;
> > struct trace_dynamic_info as_dynamic;
> > };
>
> Ok.
>
> > I could work on the part of the trace_dynamic_info if you want.
>
> Whatever you prefer. Should i update my patch and send it again, or do
> you want to adjust it?
>
How quickly do you need it. I can hopefully start working on it this week.
-- Steve
Steven Rostedt <[email protected]> writes:
> On Tue, 08 Aug 2023 19:33:06 +0200
> Sven Schnelle <[email protected]> wrote:
>
>> Steven Rostedt <[email protected]> writes:
>>
>> > The "dynamic" I was using wasn't about the fields were dynamic (union), but
>> > because the field the offset/len combo represents is of dynamic size. It's
>> > used all over the trace_events code.
>> >
>> > I would have in include/linux/trace_events.h (right above struct trace_entry):
>> >
>> > /* 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
>> > };
>> >
>> > And then it kernel/trace/trace.h:
>> >
>> > union trace_synthetic_field {
>> > u8 as_u8;
>> > u16 as_u16;
>> > u32 as_u32;
>> > u64 as_u64;
>> > struct trace_dynamic_info as_dynamic;
>> > };
>>
>> Ok.
>>
>> > I could work on the part of the trace_dynamic_info if you want.
>>
>> Whatever you prefer. Should i update my patch and send it again, or do
>> you want to adjust it?
>>
>
> How quickly do you need it. I can hopefully start working on it this week.
I would like to have the bugfix in as soon as possible, as this is
triggering a lot of KASAN warnings in our CI (besides breaking the
synthetic events on our platform). I sent a v2 of my patch, so we
apply that. The rest of the changes are not urgent.
Thanks
Sven