Commit 87a342f5 authored by Li Zefan's avatar Li Zefan Committed by Steven Rostedt

tracing/filters: Support filtering for char * strings

Usually, char * entries are dangerous in traces because the string
can be released whereas a pointer to it can still wait to be read from
the ring buffer.

But sometimes we can assume it's safe, like in case of RO data
(eg: __file__ or __line__, used in bkl trace event). If these RO data
are in a module and so is the call to the trace event, then it's safe,
because the ring buffer will be flushed once this module get unloaded.

To allow char * to be treated as a string:


			__field_ext(const char *, name, FILTER_PTR_STRING)


The filtering will not dereference "char *" unless the developer
explicitly sets FILTER_PTR_STR in __field_ext.
Signed-off-by: default avatarLi Zefan <>
LKML-Reference: <>
Signed-off-by: default avatarSteven Rostedt <>
parent 43b51ead
......@@ -144,6 +144,7 @@ enum {
extern int trace_define_field(struct ftrace_event_call *call,
......@@ -163,6 +163,20 @@ static int filter_pred_string(struct filter_pred *pred, void *event,
return match;
/* Filter predicate for char * pointers */
static int filter_pred_pchar(struct filter_pred *pred, void *event,
int val1, int val2)
char **addr = (char **)(event + pred->offset);
int cmp, match;
cmp = strncmp(*addr, pred->str_val, pred->str_len);
match = (!cmp) ^ pred->not;
return match;
* Filter predicate for dynamic sized arrays of characters.
* These are implemented through a list of strings at the end
......@@ -489,7 +503,8 @@ int filter_assign_type(const char *type)
static bool is_string_field(struct ftrace_event_field *field)
return field->filter_type == FILTER_DYN_STRING ||
field->filter_type == FILTER_STATIC_STRING;
field->filter_type == FILTER_STATIC_STRING ||
field->filter_type == FILTER_PTR_STRING;
static int is_legal_op(struct ftrace_event_field *field, int op)
......@@ -579,11 +594,16 @@ static int filter_add_pred(struct filter_parse_state *ps,
if (is_string_field(field)) {
pred->str_len = field->size;
if (field->filter_type == FILTER_STATIC_STRING)
fn = filter_pred_string;
else if (field->filter_type == FILTER_DYN_STRING)
fn = filter_pred_strloc;
pred->str_len = field->size;
else {
fn = filter_pred_pchar;
pred->str_len = strlen(pred->str_val);
} else {
if (field->is_signed)
ret = strict_strtoll(pred->str_val, 0, &val);
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