Re: [PATCH v2 bpf-next 2/7] bpf: move to generic BTF show support, apply it to seq files/strings
From: Yonghong Song
Date: Wed May 13 2020 - 19:04:57 EST
On 5/11/20 10:56 PM, Alan Maguire wrote:
generalize the "seq_show" seq file support in btf.c to support
a generic show callback of which we support two instances; the
current seq file show, and a show with snprintf() behaviour which
instead writes the type data to a supplied string.
Both classes of show function call btf_type_show() with different
targets; the seq file or the string to be written. In the string
case we need to track additional data - length left in string to write
and length to return that we would have written (a la snprintf).
By default show will display type information, field members and
their types and values etc, and the information is indented
based upon structure depth.
Show however supports flags which modify its behaviour:
BTF_SHOW_COMPACT - suppress newline/indent.
BTF_SHOW_NONAME - suppress show of type and member names.
BTF_SHOW_PTR_RAW - do not obfuscate pointer values.
BTF_SHOW_ZERO - show zeroed values (by default they are not shown).
Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
---
include/linux/btf.h | 33 +++
kernel/bpf/btf.c | 759 +++++++++++++++++++++++++++++++++++++++++++++-------
2 files changed, 690 insertions(+), 102 deletions(-)
diff --git a/include/linux/btf.h b/include/linux/btf.h
index 5c1ea99..d571125 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -13,6 +13,7 @@
struct btf_member;
struct btf_type;
union bpf_attr;
+struct btf_show;
extern const struct file_operations btf_fops;
@@ -46,8 +47,40 @@ int btf_get_info_by_fd(const struct btf *btf,
const struct btf_type *btf_type_id_size(const struct btf *btf,
u32 *type_id,
u32 *ret_size);
+
+/*
+ * Options to control show behaviour.
+ * - BTF_SHOW_COMPACT: no formatting around type information
+ * - BTF_SHOW_NONAME: no struct/union member names/types
+ * - BTF_SHOW_PTR_RAW: show raw (unobfuscated) pointer values;
+ * equivalent to %px.
+ * - BTF_SHOW_ZERO: show zero-valued struct/union members; they
+ * are not displayed by default
+ */
+#define BTF_SHOW_COMPACT (1ULL << 0)
+#define BTF_SHOW_NONAME (1ULL << 1)
+#define BTF_SHOW_PTR_RAW (1ULL << 2)
+#define BTF_SHOW_ZERO (1ULL << 3)
+
void btf_type_seq_show(const struct btf *btf, u32 type_id, void *obj,
struct seq_file *m);
+
+/*
+ * Copy len bytes of string representation of obj of BTF type_id into buf.
+ *
+ * @btf: struct btf object
+ * @type_id: type id of type obj points to
+ * @obj: pointer to typed data
+ * @buf: buffer to write to
+ * @len: maximum length to write to buf
+ * @flags: show options (see above)
+ *
+ * Return: length that would have been/was copied as per snprintf, or
+ * negative error.
+ */
+int btf_type_snprintf_show(const struct btf *btf, u32 type_id, void *obj,
+ char *buf, int len, u64 flags);
+
int btf_get_fd_by_id(u32 id);
u32 btf_id(const struct btf *btf);
bool btf_member_is_reg_int(const struct btf *btf, const struct btf_type *s,
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index dcd2331..edf6455 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -281,6 +281,32 @@ static const char *btf_type_str(const struct btf_type *t)
return btf_kind_str[BTF_INFO_KIND(t->info)];
}
+/*
+ * Common data to all BTF show operations. Private show functions can add
+ * their own data to a structure containing a struct btf_show and consult it
+ * in the show callback. See btf_type_show() below.
+ */
+struct btf_show {
+ u64 flags;
+ void *target; /* target of show operation (seq file, buffer) */
+ void (*showfn)(struct btf_show *show, const char *fmt, ...);
+ const struct btf *btf;
+ /* below are used during iteration */
+ struct {
+ u8 depth;
+ u8 depth_shown;
+ u8 depth_check;
I have some difficulties to understand the relationship between
the above three variables. Could you add some comments here?
+ u8 array_member:1,
+ array_terminated:1;
+ u16 array_encoding;
+ u32 type_id;
+ const struct btf_type *type;
+ const struct btf_member *member;
+ char name[KSYM_NAME_LEN]; /* scratch space for name */
+ char type_name[KSYM_NAME_LEN]; /* scratch space for type */
KSYM_NAME_LEN is for symbol name, not for type name. But I guess in
kernel we probably do not have > 128 bytes type name so we should be
okay here.
+ } state;
+};
+
struct btf_kind_operations {
s32 (*check_meta)(struct btf_verifier_env *env,
const struct btf_type *t,
@@ -297,9 +323,9 @@ struct btf_kind_operations {
const struct btf_type *member_type);
void (*log_details)(struct btf_verifier_env *env,
const struct btf_type *t);
- void (*seq_show)(const struct btf *btf, const struct btf_type *t,
+ void (*show)(const struct btf *btf, const struct btf_type *t,
u32 type_id, void *data, u8 bits_offsets,
- struct seq_file *m);
+ struct btf_show *show);
};
static const struct btf_kind_operations * const kind_ops[NR_BTF_KINDS];
@@ -676,6 +702,340 @@ bool btf_member_is_reg_int(const struct btf *btf, const struct btf_type *s,
return true;
}
+/* Similar to btf_type_skip_modifiers() but does not skip typedefs. */
+static inline
+const struct btf_type *btf_type_skip_qualifiers(const struct btf *btf, u32 id)
+{
+ const struct btf_type *t = btf_type_by_id(btf, id);
+
+ while (btf_type_is_modifier(t) &&
+ BTF_INFO_KIND(t->info) != BTF_KIND_TYPEDEF) {
+ id = t->type;
+ t = btf_type_by_id(btf, t->type);
+ }
+
+ return t;
+}
+
+#define BTF_SHOW_MAX_ITER 10
+
+#define BTF_KIND_BIT(kind) (1ULL << kind)
+
+static inline const char *btf_show_type_name(struct btf_show *show,
+ const struct btf_type *t)
+{
+ const char *array_suffixes = "[][][][][][][][][][]";
Add a comment here saying length BTF_SHOW_MAX_ITER * 2
so later on if somebody changes the BTF_SHOW_MAX_ITER from 10 to 12,
it won't miss here?
+ const char *array_suffix = &array_suffixes[strlen(array_suffixes)];
+ const char *ptr_suffixes = "**********";
The same here.
+ const char *ptr_suffix = &ptr_suffixes[strlen(ptr_suffixes)];
+ const char *type_name = NULL, *prefix = "", *parens = "";
+ const struct btf_array *array;
+ u32 id = show->state.type_id;
+ bool allow_anon = true;
+ u64 kinds = 0;
+ int i;
+
+ show->state.type_name[0] = '\0';
+
+ /*
+ * Start with type_id, as we have have resolved the struct btf_type *
+ * via btf_modifier_show() past the parent typedef to the child
+ * struct, int etc it is defined as. In such cases, the type_id
+ * still represents the starting type while the the struct btf_type *
+ * in our show->state points at the resolved type of the typedef.
+ */
+ t = btf_type_by_id(show->btf, id);
+ if (!t)
+ return show->state.type_name;
+
+ /*
+ * The goal here is to build up the right number of pointer and
+ * array suffixes while ensuring the type name for a typedef
+ * is represented. Along the way we accumulate a list of
+ * BTF kinds we have encountered, since these will inform later
+ * display; for example, pointer types will not require an
+ * opening "{" for struct, we will just display the pointer value.
+ *
+ * We also want to accumulate the right number of pointer or array
+ * indices in the format string while iterating until we get to
+ * the typedef/pointee/array member target type.
+ *
+ * We start by pointing at the end of pointer and array suffix
+ * strings; as we accumulate pointers and arrays we move the pointer
+ * or array string backwards so it will show the expected number of
+ * '*' or '[]' for the type. BTF_SHOW_MAX_ITER of nesting of pointers
+ * and/or arrays and typedefs are supported as a precaution.
+ *
+ * We also want to get typedef name while proceeding to resolve
+ * type it points to so that we can add parentheses if it is a
+ * "typedef struct" etc.
+ */
+ for (i = 0; i < BTF_SHOW_MAX_ITER; i++) {
+
+ switch (BTF_INFO_KIND(t->info)) {
+ case BTF_KIND_TYPEDEF:
+ if (!type_name)
+ type_name = btf_name_by_offset(show->btf,
+ t->name_off);
+ kinds |= BTF_KIND_BIT(BTF_KIND_TYPEDEF);
+ id = t->type;
+ break;
+ case BTF_KIND_ARRAY:
+ kinds |= BTF_KIND_BIT(BTF_KIND_ARRAY);
+ parens = "[";
+ array = btf_type_array(t);
+ if (!array)
+ return show->state.type_name;
+ if (!t)
+ return show->state.type_name;
+ if (array_suffix > array_suffixes)
+ array_suffix -= 2;
+ id = array->type;
+ break;
+ case BTF_KIND_PTR:
+ kinds |= BTF_KIND_BIT(BTF_KIND_PTR);
+ if (ptr_suffix > ptr_suffixes)
+ ptr_suffix -= 1;
+ id = t->type;
+ break;
+ default:
+ id = 0;
+ break;
+ }
+ if (!id)
+ break;
+ t = btf_type_skip_qualifiers(show->btf, id);
+ if (!t)
+ return show->state.type_name;
+ }
Do we do pointer tracing here? For example
struct t {
int *m[5];
}
When trying to access memory, the above code may go through
ptr->array and out of loop when hitting array element type "int"?
+ /* We may not be able to represent this type; bail to be safe */
+ if (i == BTF_SHOW_MAX_ITER)
+ return show->state.type_name;
+
+ if (!type_name)
+ type_name = btf_name_by_offset(show->btf, t->name_off);
+
+ switch (BTF_INFO_KIND(t->info)) {
+ case BTF_KIND_STRUCT:
+ case BTF_KIND_UNION:
+ prefix = BTF_INFO_KIND(t->info) == BTF_KIND_STRUCT ?
+ "struct" : "union";
+ /* if it's an array of struct/union, parens is already set */
+ if (!(kinds & (BTF_KIND_BIT(BTF_KIND_ARRAY))))
+ parens = "{";
+ break;
+ case BTF_KIND_ENUM:
+ prefix = "enum";
+ break;
+ default:
+ allow_anon = false;
+ break;
+ }
+
+ /* pointer does not require parens */
+ if (kinds & BTF_KIND_BIT(BTF_KIND_PTR))
+ parens = "";
+ /* typedef does not require struct/union/enum prefix */
+ if (kinds & BTF_KIND_BIT(BTF_KIND_TYPEDEF))
+ prefix = "";
+
+ if (!type_name || strlen(type_name) == 0) {
+ if (allow_anon)
+ type_name = "";
+ else
+ return show->state.type_name;
+ }
+
+ /* Even if we don't want type name info, we want parentheses etc */
+ if (show->flags & BTF_SHOW_NONAME)
+ snprintf(show->state.type_name, sizeof(show->state.type_name),
+ "%s", parens);
+ else
+ snprintf(show->state.type_name, sizeof(show->state.type_name),
+ "(%s%s%s%s%s%s)%s",
+ prefix,
+ strlen(prefix) > 0 && strlen(type_name) > 0 ? " " : "",
+ type_name,
+ strlen(ptr_suffix) > 0 ? " " : "", ptr_suffix,
+ array_suffix, parens);
+
+ return show->state.type_name;
+}
+
+static inline const char *btf_show_name(struct btf_show *show)
+{
+ const struct btf_type *t = show->state.type;
+ const struct btf_member *m = show->state.member;
+ const char *member = NULL;
+ const char *type = "";
+
+ show->state.name[0] = '\0';
+
+ if ((!m && !t) || show->state.array_member)
+ return show->state.name;
+
+ if (m)
+ t = btf_type_skip_qualifiers(show->btf, m->type);
+
+ if (t) {
+ type = btf_show_type_name(show, t);
+ if (!type)
+ return show->state.name;
+ }
+
+ if (m && !(show->flags & BTF_SHOW_NONAME)) {
+ member = btf_name_by_offset(show->btf, m->name_off);
+ if (member && strlen(member) > 0) {
+ snprintf(show->state.name, sizeof(show->state.name),
+ ".%s = %s", member, type);
+ return show->state.name;
+ }
+ }
+
+ snprintf(show->state.name, sizeof(show->state.name), "%s", type);
+
+ return show->state.name;
+}
+
+#define btf_show(show, ...) \
+ do { \
+ if (!show->state.depth_check) \
As I mentioned above, some comments will be good to understand here.
+ show->showfn(show, __VA_ARGS__); \
+ } while (0)
+
+static inline const char *__btf_show_indent(struct btf_show *show)
+{
+ const char *indents = " ";
+ const char *indent = &indents[strlen(indents)];
+
+ if ((indent - show->state.depth) >= indents)
+ return indent - show->state.depth;
+ return indents;
+}
+
+#define btf_show_indent(show) \
+ ((show->flags & BTF_SHOW_COMPACT) ? "" : __btf_show_indent(show))
+
+#define btf_show_newline(show) \
+ ((show->flags & BTF_SHOW_COMPACT) ? "" : "\n")
+
+#define btf_show_delim(show) \
+ (show->state.depth == 0 ? "" : \
+ ((show->flags & BTF_SHOW_COMPACT) && show->state.type && \
+ BTF_INFO_KIND(show->state.type->info) == BTF_KIND_UNION) ? "|" : ",")
+
+#define btf_show_type_value(show, fmt, value) \
+ do { \
+ if ((value) != 0 || (show->flags & BTF_SHOW_ZERO) || \
+ show->state.depth == 0) { \
+ btf_show(show, "%s%s" fmt "%s%s", \
+ btf_show_indent(show), \
+ btf_show_name(show), \
+ value, btf_show_delim(show), \
+ btf_show_newline(show)); \
+ if (show->state.depth > show->state.depth_shown) \
+ show->state.depth_shown = show->state.depth; \
+ } \
+ } while (0)
+
+#define btf_show_type_values(show, fmt, ...) \
+ do { \
+ btf_show(show, "%s%s" fmt "%s%s", btf_show_indent(show), \
+ btf_show_name(show), \
+ __VA_ARGS__, btf_show_delim(show), \
+ btf_show_newline(show)); \
+ if (show->state.depth > show->state.depth_shown) \
+ show->state.depth_shown = show->state.depth; \
+ } while (0)
+
[...]
static int btf_array_check_member(struct btf_verifier_env *env,
@@ -2104,28 +2489,87 @@ static void btf_array_log(struct btf_verifier_env *env,
array->type, array->index_type, array->nelems);
}
-static void btf_array_seq_show(const struct btf *btf, const struct btf_type *t,
- u32 type_id, void *data, u8 bits_offset,
- struct seq_file *m)
+static void __btf_array_show(const struct btf *btf, const struct btf_type *t,
+ u32 type_id, void *data, u8 bits_offset,
+ struct btf_show *show)
{
const struct btf_array *array = btf_type_array(t);
const struct btf_kind_operations *elem_ops;
const struct btf_type *elem_type;
- u32 i, elem_size, elem_type_id;
+ u32 i, elem_size = 0, elem_type_id;
+ u16 encoding = 0;
elem_type_id = array->type;
- elem_type = btf_type_id_size(btf, &elem_type_id, &elem_size);
+ elem_type = btf_type_skip_modifiers(btf, elem_type_id, NULL);
+ if (elem_type && btf_type_has_size(elem_type))
+ elem_size = elem_type->size;
+
+ if (elem_type && btf_type_is_int(elem_type)) {
+ u32 int_type = btf_type_int(elem_type);
+
+ encoding = BTF_INT_ENCODING(int_type);
+
+ /*
+ * BTF_INT_CHAR encoding never seems to be set for
+ * char arrays, so if size is 1 and element is
+ * printable as a char, we'll do that.
+ */
+ if (elem_size == 1) > + encoding = BTF_INT_CHAR;
Some char array may be printable and some may not be printable,
how did you differentiate this?
+ }
+
+ btf_show_start_array_type(show, t, type_id, encoding);
+
+ if (!elem_type)
+ goto out;
elem_ops = btf_type_ops(elem_type);
- seq_puts(m, "[");
+
for (i = 0; i < array->nelems; i++) {
- if (i)
- seq_puts(m, ",");
- elem_ops->seq_show(btf, elem_type, elem_type_id, data,
- bits_offset, m);
+ btf_show_start_array_member(show);
+
+ elem_ops->show(btf, elem_type, elem_type_id, data,
+ bits_offset, show);
data += elem_size;
+
+ btf_show_end_array_member(show);
+
+ if (show->state.array_terminated)
+ break;
}
- seq_puts(m, "]");
+out:
+ btf_show_end_array_type(show);
+}
+
[...]