kernel/trace/trace_btf.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/btf.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/kallsyms.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;

	if (unlikely(in_atomic() || irqs_disabled()))
		return NULL;

	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;
}

#define BTF_ANON_STACK_MAX	16

struct btf_anon_stack {
	u32 tid;
	u32 offset;
};

/**
 * btf_find_struct_member() - Find a member of data structure/union by name
 * @btf: Pointer to BTF object.
 * @type: Pointer to the struct/union BTF type to search within.
 * @member_name: Name of the member to find.
 * @anon_offset: Pointer to store bit offset of enclosing anonymous union/struct.
 * @container_type: Pointer to store the actual containing struct/union type.
 *
 * Find a member of data structure/union by name, traversing into anonymous
 * unions and structures if necessary.
 *
 * If the member is inside an anonymous union/structure, the bit offset
 * of that anonymous union/structure from @type is stored into @anon_offset.
 * If @container_type is non-NULL, the actual struct/union BTF type that
 * directly contains the found member is stored into @container_type.
 *
 * Return:
 * * Pointer to &struct btf_member on success.
 * * %NULL if the member was not found.
 * * %ERR_PTR(-EINVAL) if @type is not a struct/union.
 * * %ERR_PTR(-ENOMEM) if memory allocation failed.
 */
const struct btf_member *btf_find_struct_member(struct btf *btf,
						const struct btf_type *type,
						const char *member_name,
						u32 *anon_offset,
						const struct btf_type **container_type)
{
	struct btf_anon_stack *anon_stack;
	const struct btf_member *member;
	const struct btf_type *mtype;
	u32 tid, cur_offset = 0;
	const char *name;
	int i, top = 0;

	if (!btf_type_is_struct(type))
		return ERR_PTR(-EINVAL);

	anon_stack = kzalloc_objs(*anon_stack, BTF_ANON_STACK_MAX);
	if (!anon_stack)
		return ERR_PTR(-ENOMEM);

retry:
	for_each_member(i, type, member) {
		if (!member->name_off) {
			/* Anonymous union/struct: push it for later use */
			mtype = btf_type_skip_modifiers(btf, member->type, &tid);
			if (mtype && btf_type_is_struct(mtype) &&
			    top < BTF_ANON_STACK_MAX) {
				anon_stack[top].tid = tid;
				anon_stack[top++].offset = cur_offset +
					__btf_member_bit_offset(type, member);
			}
		} else {
			name = btf_name_by_offset(btf, member->name_off);
			if (name && !strcmp(member_name, name)) {
				if (anon_offset)
					*anon_offset = cur_offset;
				if (container_type)
					*container_type = type;
				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;
}

void btf_trim_retval(unsigned long func, unsigned long *retval, bool *print_retval,
			int *fmt, bool hex)
{
	const struct btf_type *t;
	char name[KSYM_NAME_LEN];
	struct btf *btf;
	u32 v, msb;
	bool signed_type;
	int kind;

	if (lookup_symbol_name(func, name))
		return;

	t = btf_find_func_proto(name, &btf);
	if (IS_ERR_OR_NULL(t))
		return;

	t = btf_type_skip_modifiers(btf, t->type, NULL);
	kind = t ? BTF_INFO_KIND(t->info) : BTF_KIND_UNKN;
	switch (kind) {
	case BTF_KIND_UNKN:
		*print_retval = false;
		break;
	case BTF_KIND_STRUCT:
	case BTF_KIND_UNION:
	case BTF_KIND_ENUM:
	case BTF_KIND_ENUM64:
		if (kind == BTF_KIND_STRUCT || kind == BTF_KIND_UNION) {
			*fmt = RETVAL_FMT_HEX;
			signed_type = false;
		} else {
			*fmt = RETVAL_FMT_DEC;
			signed_type = btf_type_kflag(t);
			if (!signed_type)
				*fmt |= RETVAL_FMT_UNSIGNED;
		}

		if (t->size > sizeof(unsigned long)) {
			*fmt |= RETVAL_FMT_TRUNC;
			msb = BITS_PER_LONG - 1;
		} else {
			msb = min_t(u32, BITS_PER_BYTE * t->size - 1,
				    BITS_PER_LONG - 1);
			*retval &= GENMASK(msb, 0);
		}
		if (signed_type && t->size && !hex)
			*retval = sign_extend64(*retval, msb);
		break;
	case BTF_KIND_INT:
		v = *(u32 *)(t + 1);
		signed_type = false;
		if (BTF_INT_ENCODING(v) == BTF_INT_BOOL) {
			*fmt = RETVAL_FMT_BOOL;
			msb = 0;
		} else {
			signed_type = BTF_INT_ENCODING(v) & BTF_INT_SIGNED;
			if (signed_type)
				*fmt = RETVAL_FMT_DEC;
			else
				*fmt = RETVAL_FMT_HEX;

			if (t->size > sizeof(unsigned long)) {
				*fmt |= RETVAL_FMT_TRUNC;
				msb = BITS_PER_LONG - 1;
			} else {
				msb = min_t(u32, BTF_INT_BITS(v) - 1,
					    BITS_PER_LONG - 1);
			}
		}
		*retval &= GENMASK(msb, 0);
		if (signed_type && !hex)
			*retval = sign_extend64(*retval, msb);
		break;
	default:
		*fmt = RETVAL_FMT_HEX;
		break;
	}

	if (*print_retval)
		*fmt |= RETVAL_FMT_BTF;
	btf_put(btf);
}