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tracing/probes: Support BTF field access from $retval
Support BTF argument on '$retval' for function return events including kretprobe and fprobe for accessing the return value. This also allows user to access its fields if the return value is a pointer of a data structure. E.g. # echo 'f getname_flags%return +0($retval->name):string' \ > dynamic_events # echo 1 > events/fprobes/getname_flags__exit/enable # ls > /dev/null # head -n 40 trace | tail ls-87 [000] ...1. 8067.616101: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./function_profile_enabled" ls-87 [000] ...1. 8067.616108: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./trace_stat" ls-87 [000] ...1. 8067.616115: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./set_graph_notrace" ls-87 [000] ...1. 8067.616122: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./set_graph_function" ls-87 [000] ...1. 8067.616129: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./set_ftrace_notrace" ls-87 [000] ...1. 8067.616135: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./set_ftrace_filter" ls-87 [000] ...1. 8067.616143: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./touched_functions" ls-87 [000] ...1. 8067.616237: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./enabled_functions" ls-87 [000] ...1. 8067.616245: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./available_filter_functions" ls-87 [000] ...1. 8067.616253: getname_flags__exit: (vfs_fstatat+0x3c/0x70 <- getname_flags) arg1="./set_ftrace_notrace_pid" Link: https://lore.kernel.org/all/169272158234.160970.2446691104240645205.stgit@devnote2/ Signed-off-by: Masami Hiramatsu (Google) <[email protected]> Acked-by: Steven Rostedt (Google) <[email protected]>
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2 files changed

+86
-102
lines changed

2 files changed

+86
-102
lines changed

‎kernel/trace/trace_probe.c

Lines changed: 85 additions & 102 deletions
Original file line numberDiff line numberDiff line change
@@ -364,45 +364,54 @@ static const char *fetch_type_from_btf_type(struct btf *btf,
364364
return NULL;
365365
}
366366

367-
static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr,
368-
struct btf **btf_p, bool tracepoint)
367+
static int query_btf_context(struct traceprobe_parse_context *ctx)
369368
{
370369
const struct btf_param *param;
371-
const struct btf_type *t;
370+
const struct btf_type *type;
372371
struct btf *btf;
372+
s32 nr;
373373

374-
if (!funcname || !nr)
375-
return ERR_PTR(-EINVAL);
374+
if (ctx->btf)
375+
return 0;
376376

377-
t = btf_find_func_proto(funcname, &btf);
378-
if (!t)
379-
return (const struct btf_param *)t;
377+
if (!ctx->funcname)
378+
return -EINVAL;
380379

381-
param = btf_get_func_param(t, nr);
382-
if (IS_ERR_OR_NULL(param))
383-
goto err;
380+
type = btf_find_func_proto(ctx->funcname, &btf);
381+
if (!type)
382+
return -ENOENT;
384383

385-
/* Hide the first 'data' argument of tracepoint */
386-
if (tracepoint) {
387-
(*nr)--;
388-
param++;
384+
ctx->btf = btf;
385+
ctx->proto = type;
386+
387+
/* ctx->params is optional, since func(void) will not have params. */
388+
nr = 0;
389+
param = btf_get_func_param(type, &nr);
390+
if (!IS_ERR_OR_NULL(param)) {
391+
/* Hide the first 'data' argument of tracepoint */
392+
if (ctx->flags & TPARG_FL_TPOINT) {
393+
nr--;
394+
param++;
395+
}
389396
}
390397

391-
if (*nr > 0) {
392-
*btf_p = btf;
393-
return param;
398+
if (nr > 0) {
399+
ctx->nr_params = nr;
400+
ctx->params = param;
401+
} else {
402+
ctx->nr_params = 0;
403+
ctx->params = NULL;
394404
}
395405

396-
err:
397-
btf_put(btf);
398-
return NULL;
406+
return 0;
399407
}
400408

401409
static void clear_btf_context(struct traceprobe_parse_context *ctx)
402410
{
403411
if (ctx->btf) {
404412
btf_put(ctx->btf);
405413
ctx->btf = NULL;
414+
ctx->proto = NULL;
406415
ctx->params = NULL;
407416
ctx->nr_params = 0;
408417
}
@@ -522,7 +531,7 @@ static int parse_btf_arg(char *varname,
522531
const struct btf_param *params;
523532
const struct btf_type *type;
524533
char *field = NULL;
525-
int i, is_ptr;
534+
int i, is_ptr, ret;
526535
u32 tid;
527536

528537
if (WARN_ON_ONCE(!ctx->funcname))
@@ -538,17 +547,37 @@ static int parse_btf_arg(char *varname,
538547
return -EOPNOTSUPP;
539548
}
540549

541-
if (!ctx->params) {
542-
params = find_btf_func_param(ctx->funcname,
543-
&ctx->nr_params, &ctx->btf,
544-
ctx->flags & TPARG_FL_TPOINT);
545-
if (IS_ERR_OR_NULL(params)) {
550+
if (ctx->flags & TPARG_FL_RETURN) {
551+
if (strcmp(varname, "$retval") != 0) {
552+
trace_probe_log_err(ctx->offset, NO_BTFARG);
553+
return -ENOENT;
554+
}
555+
code->op = FETCH_OP_RETVAL;
556+
/* Check whether the function return type is not void */
557+
if (query_btf_context(ctx) == 0) {
558+
if (ctx->proto->type == 0) {
559+
trace_probe_log_err(ctx->offset, NO_RETVAL);
560+
return -ENOENT;
561+
}
562+
tid = ctx->proto->type;
563+
goto found;
564+
}
565+
if (field) {
566+
trace_probe_log_err(ctx->offset + field - varname,
567+
NO_BTF_ENTRY);
568+
return -ENOENT;
569+
}
570+
return 0;
571+
}
572+
573+
if (!ctx->btf) {
574+
ret = query_btf_context(ctx);
575+
if (ret < 0 || ctx->nr_params == 0) {
546576
trace_probe_log_err(ctx->offset, NO_BTF_ENTRY);
547577
return PTR_ERR(params);
548578
}
549-
ctx->params = params;
550-
} else
551-
params = ctx->params;
579+
}
580+
params = ctx->params;
552581

553582
for (i = 0; i < ctx->nr_params; i++) {
554583
const char *name = btf_name_by_offset(ctx->btf, params[i].name_off);
@@ -559,7 +588,6 @@ static int parse_btf_arg(char *varname,
559588
code->param = i + 1;
560589
else
561590
code->param = i;
562-
563591
tid = params[i].type;
564592
goto found;
565593
}
@@ -584,7 +612,7 @@ static int parse_btf_arg(char *varname,
584612
return 0;
585613
}
586614

587-
static const struct fetch_type *parse_btf_arg_type(
615+
static const struct fetch_type *find_fetch_type_from_btf_type(
588616
struct traceprobe_parse_context *ctx)
589617
{
590618
struct btf *btf = ctx->btf;
@@ -596,27 +624,6 @@ static const struct fetch_type *parse_btf_arg_type(
596624
return find_fetch_type(typestr, ctx->flags);
597625
}
598626

599-
static const struct fetch_type *parse_btf_retval_type(
600-
struct traceprobe_parse_context *ctx)
601-
{
602-
const char *typestr = NULL;
603-
const struct btf_type *type;
604-
struct btf *btf;
605-
606-
if (ctx->funcname) {
607-
/* Do not use ctx->btf, because it must be used with ctx->param */
608-
type = btf_find_func_proto(ctx->funcname, &btf);
609-
if (type) {
610-
type = btf_type_skip_modifiers(btf, type->type, NULL);
611-
if (!IS_ERR_OR_NULL(type))
612-
typestr = fetch_type_from_btf_type(btf, type, ctx);
613-
btf_put(btf);
614-
}
615-
}
616-
617-
return find_fetch_type(typestr, ctx->flags);
618-
}
619-
620627
static int parse_btf_bitfield(struct fetch_insn **pcode,
621628
struct traceprobe_parse_context *ctx)
622629
{
@@ -639,30 +646,15 @@ static int parse_btf_bitfield(struct fetch_insn **pcode,
639646
return 0;
640647
}
641648

642-
static bool is_btf_retval_void(const char *funcname)
643-
{
644-
const struct btf_type *t;
645-
struct btf *btf;
646-
bool ret;
647-
648-
t = btf_find_func_proto(funcname, &btf);
649-
if (!t)
650-
return false;
651-
652-
ret = (t->type == 0);
653-
btf_put(btf);
654-
return ret;
655-
}
656649
#else
657650
static void clear_btf_context(struct traceprobe_parse_context *ctx)
658651
{
659652
ctx->btf = NULL;
660653
}
661654

662-
static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr,
663-
struct btf **btf_p, bool tracepoint)
655+
static int query_btf_context(struct traceprobe_parse_context *ctx)
664656
{
665-
return ERR_PTR(-EOPNOTSUPP);
657+
return -EOPNOTSUPP;
666658
}
667659

668660
static int parse_btf_arg(char *varname,
@@ -680,24 +672,23 @@ static int parse_btf_bitfield(struct fetch_insn **pcode,
680672
return -EOPNOTSUPP;
681673
}
682674

683-
#define parse_btf_arg_type(ctx) \
684-
find_fetch_type(NULL, ctx->flags)
685-
686-
#define parse_btf_retval_type(ctx) \
675+
#define find_fetch_type_from_btf_type(ctx) \
687676
find_fetch_type(NULL, ctx->flags)
688677

689-
#define is_btf_retval_void(funcname) (false)
690-
691678
#endif
692679

693680
#define PARAM_MAX_STACK (THREAD_SIZE / sizeof(unsigned long))
694681

695-
static int parse_probe_vars(char *arg, const struct fetch_type *t,
696-
struct fetch_insn *code,
682+
/* Parse $vars. @orig_arg points '$', which syncs to @ctx->offset */
683+
static int parse_probe_vars(char *orig_arg, const struct fetch_type *t,
684+
struct fetch_insn **pcode,
685+
struct fetch_insn *end,
697686
struct traceprobe_parse_context *ctx)
698687
{
699-
unsigned long param;
688+
struct fetch_insn *code = *pcode;
700689
int err = TP_ERR_BAD_VAR;
690+
char *arg = orig_arg + 1;
691+
unsigned long param;
701692
int ret = 0;
702693
int len;
703694

@@ -716,18 +707,17 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
716707
goto inval;
717708
}
718709

719-
if (strcmp(arg, "retval") == 0) {
720-
if (ctx->flags & TPARG_FL_RETURN) {
721-
if ((ctx->flags & TPARG_FL_KERNEL) &&
722-
is_btf_retval_void(ctx->funcname)) {
723-
err = TP_ERR_NO_RETVAL;
724-
goto inval;
725-
}
710+
if (str_has_prefix(arg, "retval")) {
711+
if (!(ctx->flags & TPARG_FL_RETURN)) {
712+
err = TP_ERR_RETVAL_ON_PROBE;
713+
goto inval;
714+
}
715+
if (!(ctx->flags & TPARG_FL_KERNEL) ||
716+
!IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS)) {
726717
code->op = FETCH_OP_RETVAL;
727718
return 0;
728719
}
729-
err = TP_ERR_RETVAL_ON_PROBE;
730-
goto inval;
720+
return parse_btf_arg(orig_arg, pcode, end, ctx);
731721
}
732722

733723
len = str_has_prefix(arg, "stack");
@@ -829,7 +819,7 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
829819

830820
switch (arg[0]) {
831821
case '$':
832-
ret = parse_probe_vars(arg + 1, type, code, ctx);
822+
ret = parse_probe_vars(arg, type, pcode, end, ctx);
833823
break;
834824

835825
case '%': /* named register */
@@ -1126,12 +1116,9 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
11261116
goto fail;
11271117

11281118
/* Update storing type if BTF is available */
1129-
if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) && !t) {
1130-
if (ctx->last_type)
1131-
parg->type = parse_btf_arg_type(ctx);
1132-
else if (ctx->flags & TPARG_FL_RETURN)
1133-
parg->type = parse_btf_retval_type(ctx);
1134-
}
1119+
if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) &&
1120+
!t && ctx->last_type)
1121+
parg->type = find_fetch_type_from_btf_type(ctx);
11351122

11361123
ret = -EINVAL;
11371124
/* Store operation */
@@ -1420,7 +1407,6 @@ const char **traceprobe_expand_meta_args(int argc, const char *argv[],
14201407
const struct btf_param *params = NULL;
14211408
int i, j, n, used, ret, args_idx = -1;
14221409
const char **new_argv = NULL;
1423-
int nr_params;
14241410

14251411
ret = argv_has_var_arg(argc, argv, &args_idx, ctx);
14261412
if (ret < 0)
@@ -1431,9 +1417,8 @@ const char **traceprobe_expand_meta_args(int argc, const char *argv[],
14311417
return NULL;
14321418
}
14331419

1434-
params = find_btf_func_param(ctx->funcname, &nr_params, &ctx->btf,
1435-
ctx->flags & TPARG_FL_TPOINT);
1436-
if (IS_ERR_OR_NULL(params)) {
1420+
ret = query_btf_context(ctx);
1421+
if (ret < 0 || ctx->nr_params == 0) {
14371422
if (args_idx != -1) {
14381423
/* $arg* requires BTF info */
14391424
trace_probe_log_err(0, NOSUP_BTFARG);
@@ -1442,8 +1427,6 @@ const char **traceprobe_expand_meta_args(int argc, const char *argv[],
14421427
*new_argc = argc;
14431428
return NULL;
14441429
}
1445-
ctx->params = params;
1446-
ctx->nr_params = nr_params;
14471430

14481431
if (args_idx >= 0)
14491432
*new_argc = argc + ctx->nr_params - 1;
@@ -1458,7 +1441,7 @@ const char **traceprobe_expand_meta_args(int argc, const char *argv[],
14581441
for (i = 0, j = 0; i < argc; i++) {
14591442
trace_probe_log_set_index(i + 2);
14601443
if (i == args_idx) {
1461-
for (n = 0; n < nr_params; n++) {
1444+
for (n = 0; n < ctx->nr_params; n++) {
14621445
ret = sprint_nth_btf_arg(n, "", buf + used,
14631446
bufsize - used, ctx);
14641447
if (ret < 0)

‎kernel/trace/trace_probe.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -385,6 +385,7 @@ struct traceprobe_parse_context {
385385
struct trace_event_call *event;
386386
/* BTF related parameters */
387387
const char *funcname; /* Function name in BTF */
388+
const struct btf_type *proto; /* Prototype of the function */
388389
const struct btf_param *params; /* Parameter of the function */
389390
s32 nr_params; /* The number of the parameters */
390391
struct btf *btf; /* The BTF to be used */

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