[PATCH v5 2/9] tracing/probes: Move finding func-proto API and getting func-param API to trace_btf

Masami Hiramatsu (Google)
2023-08-07T02:54:52Z

Move generic function-proto find API and getting function parameter API
to BTF library code from trace_probe.c. This will avoid redundant efforts
on different feature.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
Changes in v3:
- Remove perameter check.
- Fix a typo.
- Add a type check for btf_get_func_param() and add comment for that.
- Use bpf_find_btf_id() and add bpf_put().
- Move the code before btf_show() related code.
Changes in v5:
- Move the generic functions into a new file, trace_btf.c, for avoiding
tree-merge conflict.
---
kernel/trace/Makefile | 1 +
kernel/trace/trace_btf.c | 52 ++++++++++++++++++++++++++++++++++++++++++++
kernel/trace/trace_btf.h | 7 ++++++
kernel/trace/trace_probe.c | 51 +++++++++----------------------------------
4 files changed, 71 insertions(+), 40 deletions(-)
create mode 100644 kernel/trace/trace_btf.c
create mode 100644 kernel/trace/trace_btf.h

diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 64b61f67a403..057cd975d014 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -99,6 +99,7 @@ obj-$(CONFIG_KGDB_KDB) += trace_kdb.o
endif
obj-$(CONFIG_DYNAMIC_EVENTS) += trace_dynevent.o
obj-$(CONFIG_PROBE_EVENTS) += trace_probe.o
+obj-$(CONFIG_PROBE_EVENTS_BTF_ARGS) += trace_btf.o
obj-$(CONFIG_UPROBE_EVENTS) += trace_uprobe.o
obj-$(CONFIG_BOOTTIME_TRACING) += trace_boot.o
obj-$(CONFIG_FTRACE_RECORD_RECURSION) += trace_recursion_record.o
diff --git a/kernel/trace/trace_btf.c b/kernel/trace/trace_btf.c
new file mode 100644
index 000000000000..82cbbeeda071
--- /dev/null
+++ b/kernel/trace/trace_btf.c
@@ -0,0 +1,52 @@
+#include <linux/btf.h>
+#include <linux/kernel.h>
+
+#include "trace_btf.h"
+
+/*
+ * Find a function proto type by name, and return the btf_type with its btf
+ * in *@btf_p. Return NULL if not found.
+ * Note that caller has to call btf_put(*@btf_p) after using the btf_type.
+ */
+const struct btf_type *btf_find_func_proto(const char *func_name, struct btf **btf_p)
+{
+ const struct btf_type *t;
+ s32 id;
+
+ id = bpf_find_btf_id(func_name, BTF_KIND_FUNC, btf_p);
+ if (id < 0)
+ return NULL;
+
+ /* Get BTF_KIND_FUNC type */
+ t = btf_type_by_id(*btf_p, id);
+ if (!t || !btf_type_is_func(t))
+ goto err;
+
+ /* The type of BTF_KIND_FUNC is BTF_KIND_FUNC_PROTO */
+ t = btf_type_by_id(*btf_p, t->type);
+ if (!t || !btf_type_is_func_proto(t))
+ goto err;
+
+ return t;
+err:
+ btf_put(*btf_p);
+ return NULL;
+}
+
+/*
+ * Get function parameter with the number of parameters.
+ * This can return NULL if the function has no parameters.
+ * It can return -EINVAL if the @func_proto is not a function proto type.
+ */
+const struct btf_param *btf_get_func_param(const struct btf_type *func_proto, s32 *nr)
+{
+ if (!btf_type_is_func_proto(func_proto))
+ return ERR_PTR(-EINVAL);
+
+ *nr = btf_type_vlen(func_proto);
+ if (*nr > 0)
+ return (const struct btf_param *)(func_proto + 1);
+ else
+ return NULL;
+}
+
diff --git a/kernel/trace/trace_btf.h b/kernel/trace/trace_btf.h
new file mode 100644
index 000000000000..2ef1b2367e1e
--- /dev/null
+++ b/kernel/trace/trace_btf.h
@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/btf.h>
+
+const struct btf_type *btf_find_func_proto(const char *func_name,
+ struct btf **btf_p);
+const struct btf_param *btf_get_func_param(const struct btf_type *func_proto,
+ s32 *nr);
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index ecbe28f8d676..c3ac5698e80b 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -12,6 +12,7 @@
#define pr_fmt(fmt) "trace_probe: " fmt

#include <linux/bpf.h>
+#include "trace_btf.h"

#include "trace_probe.h"

@@ -361,38 +362,6 @@ static const char *type_from_btf_id(struct btf *btf, s32 id)
return NULL;
}

-static const struct btf_type *find_btf_func_proto(const char *funcname,
- struct btf **btf_p)
-{
- const struct btf_type *t;
- struct btf *btf = NULL;
- s32 id;
-
- if (!funcname)
- return ERR_PTR(-EINVAL);
-
- id = bpf_find_btf_id(funcname, BTF_KIND_FUNC, &btf);
- if (id <= 0)
- return ERR_PTR(-ENOENT);
-
- /* Get BTF_KIND_FUNC type */
- t = btf_type_by_id(btf, id);
- if (!t || !btf_type_is_func(t))
- goto err;
-
- /* The type of BTF_KIND_FUNC is BTF_KIND_FUNC_PROTO */
- t = btf_type_by_id(btf, t->type);
- if (!t || !btf_type_is_func_proto(t))
- goto err;
-
- *btf_p = btf;
- return t;
-
-err:
- btf_put(btf);
- return ERR_PTR(-ENOENT);
-}
-
static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr,
struct btf **btf_p, bool tracepoint)
{
@@ -403,12 +372,13 @@ static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr
if (!funcname || !nr)
return ERR_PTR(-EINVAL);

- t = find_btf_func_proto(funcname, &btf);
- if (IS_ERR(t))
+ t = btf_find_func_proto(funcname, &btf);
+ if (!t)
return (const struct btf_param *)t;

- *nr = btf_type_vlen(t);
- param = (const struct btf_param *)(t + 1);
+ param = btf_get_func_param(t, nr);
+ if (IS_ERR_OR_NULL(param))
+ goto err;

/* Hide the first 'data' argument of tracepoint */
if (tracepoint) {
@@ -421,6 +391,7 @@ static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr
return param;
}

+err:
btf_put(btf);
return NULL;
}
@@ -496,8 +467,8 @@ static const struct fetch_type *parse_btf_retval_type(

if (ctx->funcname) {
/* Do not use ctx->btf, because it must be used with ctx->param */
- t = find_btf_func_proto(ctx->funcname, &btf);
- if (!IS_ERR(t)) {
+ t = btf_find_func_proto(ctx->funcname, &btf);
+ if (t) {
typestr = type_from_btf_id(btf, t->type);
btf_put(btf);
}
@@ -512,8 +483,8 @@ static bool is_btf_retval_void(const char *funcname)
struct btf *btf;
bool ret;

- t = find_btf_func_proto(funcname, &btf);
- if (IS_ERR(t))
+ t = btf_find_func_proto(funcname, &btf);
+ if (!t)
return false;

ret = (t->type == 0);