[v6,3/9] tracing/probes: Add a function to search a member of a struct/union
Commit Message
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Add btf_find_struct_member() API to search a member of a given data structure
or union from the member's name.
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes in v3:
- Remove simple input check.
- Fix unneeded IS_ERR_OR_NULL() check for btf_type_by_id().
- Move the code next to btf_get_func_param().
- Use for_each_member() macro instead of for-loop.
- Use btf_type_skip_modifiers() instead of btf_type_by_id().
Changes in v4:
- Use a stack for searching in anonymous members instead of nested call.
Changes in v5:
- Move the generic functions into a new file, trace_btf.c, for avoiding
tree-merge conflict.
- Return anon_offset for calculating correct offset from root struct.
Changes in v6:
- Allocate anon_stack from heap instead of stack.
---
kernel/trace/trace_btf.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++
kernel/trace/trace_btf.h | 4 +++
2 files changed, 73 insertions(+)
@@ -1,6 +1,7 @@
// SPDX-License-Identifier: GPL-2.0
#include <linux/btf.h>
#include <linux/kernel.h>
+#include <linux/slab.h>
#include "trace_btf.h"
@@ -51,3 +52,71 @@ const struct btf_param *btf_get_func_param(const struct btf_type *func_proto, s3
return NULL;
}
+#define BTF_ANON_STACK_MAX 16
+
+struct btf_anon_stack {
+ u32 tid;
+ u32 offset;
+};
+
+/*
+ * Find a member of data structure/union by name and return it.
+ * Return NULL if not found, or -EINVAL if parameter is invalid.
+ * If the member is an member of anonymous union/structure, the offset
+ * of that anonymous union/structure is stored into @anon_offset. Caller
+ * can calculate the correct offset from the root data structure by
+ * adding anon_offset to the member's offset.
+ */
+const struct btf_member *btf_find_struct_member(struct btf *btf,
+ const struct btf_type *type,
+ const char *member_name,
+ u32 *anon_offset)
+{
+ struct btf_anon_stack *anon_stack;
+ const struct btf_member *member;
+ u32 tid, cur_offset = 0;
+ const char *name;
+ int i, top = 0;
+
+ anon_stack = kcalloc(BTF_ANON_STACK_MAX, sizeof(*anon_stack), GFP_KERNEL);
+ if (!anon_stack)
+ return ERR_PTR(-ENOMEM);
+
+retry:
+ if (!btf_type_is_struct(type)) {
+ member = ERR_PTR(-EINVAL);
+ goto out;
+ }
+
+ for_each_member(i, type, member) {
+ if (!member->name_off) {
+ /* Anonymous union/struct: push it for later use */
+ type = btf_type_skip_modifiers(btf, member->type, &tid);
+ if (type && top < BTF_ANON_STACK_MAX) {
+ anon_stack[top].tid = tid;
+ anon_stack[top++].offset =
+ cur_offset + member->offset;
+ }
+ } else {
+ name = btf_name_by_offset(btf, member->name_off);
+ if (name && !strcmp(member_name, name)) {
+ if (anon_offset)
+ *anon_offset = cur_offset;
+ goto out;
+ }
+ }
+ }
+ if (top > 0) {
+ /* Pop from the anonymous stack and retry */
+ tid = anon_stack[--top].tid;
+ cur_offset = anon_stack[top].offset;
+ type = btf_type_by_id(btf, tid);
+ goto retry;
+ }
+ member = NULL;
+
+out:
+ kfree(anon_stack);
+ return member;
+}
+
@@ -5,3 +5,7 @@ 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);
+const struct btf_member *btf_find_struct_member(struct btf *btf,
+ const struct btf_type *type,
+ const char *member_name,
+ u32 *anon_offset);