[PATCH v3 4/9] tracing/probes: Support BTF based data structure field access

Masami Hiramatsu (Google)
2023-07-26T13:00:51Z

Using BTF to access the fields of a data structure. You can use this
for accessing the field with '->' or '.' operation with BTF argument.

# echo 't sched_switch next=next->pid vruntime=next->se.vruntime' \
> dynamic_events
# echo 1 > events/tracepoints/sched_switch/enable
# head -n 40 trace | tail
<idle>-0 [000] d..3. 272.565382: sched_switch: (__probestub_sched_switch+0x4/0x10) next=26 vruntime=956533179
kcompactd0-26 [000] d..3. 272.565406: sched_switch: (__probestub_sched_switch+0x4/0x10) next=0 vruntime=0
<idle>-0 [000] d..3. 273.069441: sched_switch: (__probestub_sched_switch+0x4/0x10) next=9 vruntime=956533179
kworker/0:1-9 [000] d..3. 273.069464: sched_switch: (__probestub_sched_switch+0x4/0x10) next=26 vruntime=956579181
kcompactd0-26 [000] d..3. 273.069480: sched_switch: (__probestub_sched_switch+0x4/0x10) next=0 vruntime=0
<idle>-0 [000] d..3. 273.141434: sched_switch: (__probestub_sched_switch+0x4/0x10) next=22 vruntime=956533179
kworker/u2:1-22 [000] d..3. 273.141461: sched_switch: (__probestub_sched_switch+0x4/0x10) next=0 vruntime=0
<idle>-0 [000] d..3. 273.480872: sched_switch: (__probestub_sched_switch+0x4/0x10) next=22 vruntime=956585857
kworker/u2:1-22 [000] d..3. 273.480905: sched_switch: (__probestub_sched_switch+0x4/0x10) next=70 vruntime=959533179
sh-70 [000] d..3. 273.481102: sched_switch: (__probestub_sched_switch+0x4/0x10) next=0 vruntime=0

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
---
Changes in v2:
- Use new BTF API for finding the member.
Changes in v3:
- Update according to previous changes in the series.
---
kernel/trace/trace_probe.c | 226 +++++++++++++++++++++++++++++++++++++++-----
kernel/trace/trace_probe.h | 11 ++
2 files changed, 210 insertions(+), 27 deletions(-)

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 21a228d88ebb..f6b855de4256 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -309,16 +309,14 @@ static u32 btf_type_int(const struct btf_type *t)
return *(u32 *)(t + 1);
}

-static const char *type_from_btf_id(struct btf *btf, s32 id)
+static const char *fetch_type_from_btf_type(struct btf *btf,
+ const struct btf_type *type,
+ struct traceprobe_parse_context *ctx)
{
- const struct btf_type *t;
u32 intdata;
- s32 tid;

/* TODO: const char * could be converted as a string */
- t = btf_type_skip_modifiers(btf, id, &tid);
-
- switch (BTF_INFO_KIND(t->info)) {
+ switch (BTF_INFO_KIND(type->info)) {
case BTF_KIND_ENUM:
/* enum is "int", so convert to "s32" */
return "s32";
@@ -331,7 +329,7 @@ static const char *type_from_btf_id(struct btf *btf, s32 id)
else
return "x32";
case BTF_KIND_INT:
- intdata = btf_type_int(t);
+ intdata = btf_type_int(type);
if (BTF_INT_ENCODING(intdata) & BTF_INT_SIGNED) {
switch (BTF_INT_BITS(intdata)) {
case 8:
@@ -354,6 +352,10 @@ static const char *type_from_btf_id(struct btf *btf, s32 id)
case 64:
return "u64";
}
+ /* bitfield, size is encoded in the type */
+ ctx->last_bitsize = BTF_INT_BITS(intdata);
+ ctx->last_bitoffs += BTF_INT_OFFSET(intdata);
+ return "u64";
}
}
/* TODO: support other types */
@@ -405,15 +407,132 @@ static void clear_btf_context(struct traceprobe_parse_context *ctx)
}
}

-static int parse_btf_arg(const char *varname, struct fetch_insn *code,
+/* Return 1 if the field separater is arrow operator ('->') */
+static int split_next_field(char *varname, char **next_field,
+ struct traceprobe_parse_context *ctx)
+{
+ char *field;
+ int ret = 0;
+
+ field = strpbrk(varname, ".-");
+ if (field) {
+ if (field[0] == '-' && field[1] == '>') {
+ field[0] = '\0';
+ field += 2;
+ ret = 1;
+ } else if (field[0] == '.') {
+ field[0] = '\0';
+ field += 1;
+ } else {
+ trace_probe_log_err(ctx->offset + field - varname, BAD_HYPHEN);
+ return -EINVAL;
+ }
+ *next_field = field;
+ }
+
+ return ret;
+}
+
+/*
+ * Parse the field of data structure. The @type must be a pointer type
+ * pointing the target data structure type.
+ */
+static int parse_btf_field(char *fieldname, const struct btf_type *type,
+ struct fetch_insn **pcode, struct fetch_insn *end,
+ struct traceprobe_parse_context *ctx)
+{
+ struct fetch_insn *code = *pcode;
+ const struct btf_member *field;
+ u32 bitoffs;
+ char *next;
+ int is_ptr;
+ s32 tid;
+
+ do {
+ /* Outer loop for solving arrow operator ('->') */
+ if (BTF_INFO_KIND(type->info) != BTF_KIND_PTR) {
+ trace_probe_log_err(ctx->offset, NO_PTR_STRCT);
+ return -EINVAL;
+ }
+ /* Convert a struct pointer type to a struct type */
+ type = btf_type_skip_modifiers(ctx->btf, type->type, &tid);
+ if (!type) {
+ trace_probe_log_err(ctx->offset, BAD_BTF_TID);
+ return -EINVAL;
+ }
+
+ bitoffs = 0;
+ do {
+ /* Inner loop for solving dot operator ('.') */
+ next = NULL;
+ is_ptr = split_next_field(fieldname, &next, ctx);
+ if (is_ptr < 0)
+ return is_ptr;
+
+ field = btf_find_struct_member(ctx->btf, type, fieldname);
+ if (!field) {
+ trace_probe_log_err(ctx->offset, NO_BTF_FIELD);
+ return -ENOENT;
+ }
+
+ /* Accumulate the bit-offsets of the dot-connected fields */
+ if (btf_type_kflag(type)) {
+ bitoffs += BTF_MEMBER_BIT_OFFSET(field->offset);
+ ctx->last_bitsize = BTF_MEMBER_BITFIELD_SIZE(field->offset);
+ } else {
+ bitoffs += field->offset;
+ ctx->last_bitsize = 0;
+ }
+
+ type = btf_type_skip_modifiers(ctx->btf, field->type, &tid);
+ if (!type) {
+ trace_probe_log_err(ctx->offset, BAD_BTF_TID);
+ return -EINVAL;
+ }
+
+ ctx->offset += next - fieldname;
+ fieldname = next;
+ } while (!is_ptr && fieldname);
+
+ if (++code == end) {
+ trace_probe_log_err(ctx->offset, TOO_MANY_OPS);
+ return -EINVAL;
+ }
+ code->op = FETCH_OP_DEREF; /* TODO: user deref support */
+ code->offset = bitoffs / 8;
+ *pcode = code;
+
+ ctx->last_bitoffs = bitoffs % 8;
+ ctx->last_type = type;
+ } while (fieldname);
+
+ return 0;
+}
+
+static int parse_btf_arg(char *varname,
+ struct fetch_insn **pcode, struct fetch_insn *end,
struct traceprobe_parse_context *ctx)
{
+ struct fetch_insn *code = *pcode;
const struct btf_param *params;
- int i;
+ const struct btf_type *type;
+ char *field = NULL;
+ int i, is_ptr;
+ u32 tid;

if (WARN_ON_ONCE(!ctx->funcname))
return -EINVAL;

+ is_ptr = split_next_field(varname, &field, ctx);
+ if (is_ptr < 0)
+ return is_ptr;
+ if (!is_ptr && field) {
+ /* dot-connected field on an argument is not supported. */
+ trace_probe_log_err(ctx->offset + field - varname,
+ NOSUP_DAT_ARG);
+ return -EOPNOTSUPP;
+ }
+
if (!ctx->params) {
params = find_btf_func_param(ctx->funcname,
&ctx->nr_params, &ctx->btf,
@@ -435,24 +554,39 @@ static int parse_btf_arg(const char *varname, struct fetch_insn *code,
code->param = i + 1;
else
code->param = i;
- return 0;
+
+ tid = params[i].type;
+ goto found;
}
}
trace_probe_log_err(ctx->offset, NO_BTFARG);
return -ENOENT;
+
+found:
+ type = btf_type_skip_modifiers(ctx->btf, tid, &tid);
+ if (!type) {
+ trace_probe_log_err(ctx->offset, BAD_BTF_TID);
+ return -EINVAL;
+ }
+ /* Initialize the last type information */
+ ctx->last_type = type;
+ ctx->last_bitoffs = 0;
+ ctx->last_bitsize = 0;
+ if (field) {
+ ctx->offset += field - varname;
+ return parse_btf_field(field, type, pcode, end, ctx);
+ }
+ return 0;
}

-static const struct fetch_type *parse_btf_arg_type(int arg_idx,
+static const struct fetch_type *parse_btf_arg_type(
struct traceprobe_parse_context *ctx)
{
struct btf *btf = ctx->btf;
const char *typestr = NULL;

- if (btf && ctx->params) {
- if (ctx->flags & TPARG_FL_TPOINT)
- arg_idx--;
- typestr = type_from_btf_id(btf, ctx->params[arg_idx].type);
- }
+ if (btf && ctx->last_type)
+ typestr = fetch_type_from_btf_type(btf, ctx->last_type, ctx);

return find_fetch_type(typestr, ctx->flags);
}
@@ -461,14 +595,16 @@ static const struct fetch_type *parse_btf_retval_type(
struct traceprobe_parse_context *ctx)
{
const char *typestr = NULL;
- const struct btf_type *t;
+ const struct btf_type *type;
struct btf *btf;

if (ctx->funcname) {
/* Do not use ctx->btf, because it must be used with ctx->param */
- t = btf_find_func_proto(ctx->funcname, &btf);
- if (t) {
- typestr = type_from_btf_id(btf, t->type);
+ type = btf_find_func_proto(ctx->funcname, &btf);
+ if (type) {
+ type = btf_type_skip_modifiers(btf, type->type, NULL);
+ if (!IS_ERR_OR_NULL(type))
+ typestr = fetch_type_from_btf_type(btf, type, ctx);
btf_put(btf);
}
}
@@ -476,6 +612,28 @@ static const struct fetch_type *parse_btf_retval_type(
return find_fetch_type(typestr, ctx->flags);
}

+static int parse_btf_bitfield(struct fetch_insn **pcode,
+ struct traceprobe_parse_context *ctx)
+{
+ struct fetch_insn *code = *pcode;
+
+ if ((ctx->last_bitsize % 8 == 0) && ctx->last_bitoffs == 0)
+ return 0;
+
+ code++;
+ if (code->op != FETCH_OP_NOP) {
+ trace_probe_log_err(ctx->offset, TOO_MANY_OPS);
+ return -EINVAL;
+ }
+ *pcode = code;
+
+ code->op = FETCH_OP_MOD_BF;
+ code->lshift = 64 - (ctx->last_bitsize + ctx->last_bitoffs);
+ code->rshift = 64 - ctx->last_bitsize;
+ code->basesize = 64 / 8;
+ return 0;
+}
+
static bool is_btf_retval_void(const char *funcname)
{
const struct btf_type *t;
@@ -502,14 +660,22 @@ static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr
return ERR_PTR(-EOPNOTSUPP);
}

-static int parse_btf_arg(const char *varname, struct fetch_insn *code,
+static int parse_btf_arg(char *varname,
+ struct fetch_insn **pcode, struct fetch_insn *end,
struct traceprobe_parse_context *ctx)
{
trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
return -EOPNOTSUPP;
}

-#define parse_btf_arg_type(idx, ctx) \
+static int parse_btf_bitfield(struct fetch_insn **pcode,
+ struct traceprobe_parse_context *ctx)
+{
+ trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
+ return -EOPNOTSUPP;
+}
+
+#define parse_btf_arg_type(ctx) \
find_fetch_type(NULL, ctx->flags)

#define parse_btf_retval_type(ctx) \
@@ -777,6 +943,8 @@ parse_probe_arg(char *arg, const struct fetch_type *type,

code->op = deref;
code->offset = offset;
+ /* Reset the last type if used */
+ ctx->last_type = NULL;
}
break;
case '\\': /* Immediate value */
@@ -800,7 +968,7 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
return -EINVAL;
}
- ret = parse_btf_arg(arg, code, ctx);
+ ret = parse_btf_arg(arg, pcode, end, ctx);
break;
}
}
@@ -946,6 +1114,7 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
goto out;
code[FETCH_INSN_MAX - 1].op = FETCH_OP_END;

+ ctx->last_type = NULL;
ret = parse_probe_arg(arg, parg->type, &code, &code[FETCH_INSN_MAX - 1],
ctx);
if (ret)
@@ -953,9 +1122,9 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,

/* Update storing type if BTF is available */
if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) && !t) {
- if (code->op == FETCH_OP_ARG)
- parg->type = parse_btf_arg_type(code->param, ctx);
- else if (code->op == FETCH_OP_RETVAL)
+ if (ctx->last_type)
+ parg->type = parse_btf_arg_type(ctx);
+ else if (ctx->flags & TPARG_FL_RETURN)
parg->type = parse_btf_retval_type(ctx);
}

@@ -1030,6 +1199,11 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
trace_probe_log_err(ctx->offset + t - arg, BAD_BITFIELD);
goto fail;
}
+ } else if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) &&
+ ctx->last_type) {
+ ret = parse_btf_bitfield(&code, ctx);
+ if (ret)
+ goto fail;
}
ret = -EINVAL;
/* Loop(Array) operation */
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 4dc91460a75d..6111f1ffca6c 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -388,6 +388,9 @@ struct traceprobe_parse_context {
const struct btf_param *params; /* Parameter of the function */
s32 nr_params; /* The number of the parameters */
struct btf *btf; /* The BTF to be used */
+ const struct btf_type *last_type; /* Saved type */
+ u32 last_bitoffs; /* Saved bitoffs */
+ u32 last_bitsize; /* Saved bitsize */
unsigned int flags;
int offset;
};
@@ -503,7 +506,13 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call,
C(BAD_VAR_ARGS, "$arg* must be an independent parameter without name etc."),\
C(NOFENTRY_ARGS, "$arg* can be used only on function entry"), \
C(DOUBLE_ARGS, "$arg* can be used only once in the parameters"), \
- C(ARGS_2LONG, "$arg* failed because the argument list is too long"),
+ C(ARGS_2LONG, "$arg* failed because the argument list is too long"), \
+ C(ARGIDX_2BIG, "$argN index is too big"), \
+ C(NO_PTR_STRCT, "This is not a pointer to union/structure."), \
+ C(NOSUP_DAT_ARG, "Non pointer structure/union argument is not supported."),\
+ C(BAD_HYPHEN, "Failed to parse single hyphen. Forgot '>'?"), \
+ C(NO_BTF_FIELD, "This field is not found."), \
+ C(BAD_BTF_TID, "Failed to get BTF type info."),

#undef C
#define C(a, b) TP_ERR_##a