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![Gustavo A. R. Silva](/assets/img/avatar_default.png)
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293
("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200507185057.GA13981@embeddedor
236 lines
7.6 KiB
C
236 lines
7.6 KiB
C
/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
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/*
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* Internal libbpf helpers.
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*
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* Copyright (c) 2019 Facebook
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*/
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#ifndef __LIBBPF_LIBBPF_INTERNAL_H
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#define __LIBBPF_LIBBPF_INTERNAL_H
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#include "libbpf.h"
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#define BTF_INFO_ENC(kind, kind_flag, vlen) \
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((!!(kind_flag) << 31) | ((kind) << 24) | ((vlen) & BTF_MAX_VLEN))
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#define BTF_TYPE_ENC(name, info, size_or_type) (name), (info), (size_or_type)
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#define BTF_INT_ENC(encoding, bits_offset, nr_bits) \
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((encoding) << 24 | (bits_offset) << 16 | (nr_bits))
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#define BTF_TYPE_INT_ENC(name, encoding, bits_offset, bits, sz) \
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BTF_TYPE_ENC(name, BTF_INFO_ENC(BTF_KIND_INT, 0, 0), sz), \
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BTF_INT_ENC(encoding, bits_offset, bits)
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#define BTF_MEMBER_ENC(name, type, bits_offset) (name), (type), (bits_offset)
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#define BTF_PARAM_ENC(name, type) (name), (type)
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#define BTF_VAR_SECINFO_ENC(type, offset, size) (type), (offset), (size)
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#ifndef min
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# define min(x, y) ((x) < (y) ? (x) : (y))
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#endif
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#ifndef max
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# define max(x, y) ((x) < (y) ? (y) : (x))
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#endif
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#ifndef offsetofend
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# define offsetofend(TYPE, FIELD) \
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(offsetof(TYPE, FIELD) + sizeof(((TYPE *)0)->FIELD))
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#endif
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/* Symbol versioning is different between static and shared library.
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* Properly versioned symbols are needed for shared library, but
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* only the symbol of the new version is needed for static library.
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*/
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#ifdef SHARED
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# define COMPAT_VERSION(internal_name, api_name, version) \
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asm(".symver " #internal_name "," #api_name "@" #version);
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# define DEFAULT_VERSION(internal_name, api_name, version) \
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asm(".symver " #internal_name "," #api_name "@@" #version);
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#else
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# define COMPAT_VERSION(internal_name, api_name, version)
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# define DEFAULT_VERSION(internal_name, api_name, version) \
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extern typeof(internal_name) api_name \
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__attribute__((alias(#internal_name)));
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#endif
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extern void libbpf_print(enum libbpf_print_level level,
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const char *format, ...)
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__attribute__((format(printf, 2, 3)));
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#define __pr(level, fmt, ...) \
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do { \
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libbpf_print(level, "libbpf: " fmt, ##__VA_ARGS__); \
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} while (0)
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#define pr_warn(fmt, ...) __pr(LIBBPF_WARN, fmt, ##__VA_ARGS__)
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#define pr_info(fmt, ...) __pr(LIBBPF_INFO, fmt, ##__VA_ARGS__)
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#define pr_debug(fmt, ...) __pr(LIBBPF_DEBUG, fmt, ##__VA_ARGS__)
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static inline bool libbpf_validate_opts(const char *opts,
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size_t opts_sz, size_t user_sz,
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const char *type_name)
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{
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if (user_sz < sizeof(size_t)) {
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pr_warn("%s size (%zu) is too small\n", type_name, user_sz);
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return false;
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}
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if (user_sz > opts_sz) {
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size_t i;
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for (i = opts_sz; i < user_sz; i++) {
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if (opts[i]) {
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pr_warn("%s has non-zero extra bytes\n",
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type_name);
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return false;
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}
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}
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}
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return true;
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}
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#define OPTS_VALID(opts, type) \
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(!(opts) || libbpf_validate_opts((const char *)opts, \
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offsetofend(struct type, \
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type##__last_field), \
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(opts)->sz, #type))
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#define OPTS_HAS(opts, field) \
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((opts) && opts->sz >= offsetofend(typeof(*(opts)), field))
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#define OPTS_GET(opts, field, fallback_value) \
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(OPTS_HAS(opts, field) ? (opts)->field : fallback_value)
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int parse_cpu_mask_str(const char *s, bool **mask, int *mask_sz);
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int parse_cpu_mask_file(const char *fcpu, bool **mask, int *mask_sz);
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int libbpf__load_raw_btf(const char *raw_types, size_t types_len,
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const char *str_sec, size_t str_len);
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int bpf_object__section_size(const struct bpf_object *obj, const char *name,
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__u32 *size);
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int bpf_object__variable_offset(const struct bpf_object *obj, const char *name,
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__u32 *off);
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struct nlattr;
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typedef int (*libbpf_dump_nlmsg_t)(void *cookie, void *msg, struct nlattr **tb);
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int libbpf_netlink_open(unsigned int *nl_pid);
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int libbpf_nl_get_link(int sock, unsigned int nl_pid,
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libbpf_dump_nlmsg_t dump_link_nlmsg, void *cookie);
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int libbpf_nl_get_class(int sock, unsigned int nl_pid, int ifindex,
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libbpf_dump_nlmsg_t dump_class_nlmsg, void *cookie);
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int libbpf_nl_get_qdisc(int sock, unsigned int nl_pid, int ifindex,
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libbpf_dump_nlmsg_t dump_qdisc_nlmsg, void *cookie);
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int libbpf_nl_get_filter(int sock, unsigned int nl_pid, int ifindex, int handle,
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libbpf_dump_nlmsg_t dump_filter_nlmsg, void *cookie);
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struct btf_ext_info {
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/*
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* info points to the individual info section (e.g. func_info and
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* line_info) from the .BTF.ext. It does not include the __u32 rec_size.
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*/
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void *info;
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__u32 rec_size;
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__u32 len;
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};
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#define for_each_btf_ext_sec(seg, sec) \
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for (sec = (seg)->info; \
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(void *)sec < (seg)->info + (seg)->len; \
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sec = (void *)sec + sizeof(struct btf_ext_info_sec) + \
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(seg)->rec_size * sec->num_info)
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#define for_each_btf_ext_rec(seg, sec, i, rec) \
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for (i = 0, rec = (void *)&(sec)->data; \
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i < (sec)->num_info; \
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i++, rec = (void *)rec + (seg)->rec_size)
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struct btf_ext {
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union {
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struct btf_ext_header *hdr;
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void *data;
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};
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struct btf_ext_info func_info;
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struct btf_ext_info line_info;
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struct btf_ext_info field_reloc_info;
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__u32 data_size;
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};
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struct btf_ext_info_sec {
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__u32 sec_name_off;
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__u32 num_info;
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/* Followed by num_info * record_size number of bytes */
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__u8 data[];
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};
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/* The minimum bpf_func_info checked by the loader */
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struct bpf_func_info_min {
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__u32 insn_off;
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__u32 type_id;
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};
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/* The minimum bpf_line_info checked by the loader */
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struct bpf_line_info_min {
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__u32 insn_off;
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__u32 file_name_off;
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__u32 line_off;
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__u32 line_col;
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};
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/* bpf_field_info_kind encodes which aspect of captured field has to be
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* adjusted by relocations. Currently supported values are:
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* - BPF_FIELD_BYTE_OFFSET: field offset (in bytes);
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* - BPF_FIELD_EXISTS: field existence (1, if field exists; 0, otherwise);
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*/
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enum bpf_field_info_kind {
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BPF_FIELD_BYTE_OFFSET = 0, /* field byte offset */
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BPF_FIELD_BYTE_SIZE = 1,
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BPF_FIELD_EXISTS = 2, /* field existence in target kernel */
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BPF_FIELD_SIGNED = 3,
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BPF_FIELD_LSHIFT_U64 = 4,
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BPF_FIELD_RSHIFT_U64 = 5,
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};
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/* The minimum bpf_field_reloc checked by the loader
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*
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* Field relocation captures the following data:
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* - insn_off - instruction offset (in bytes) within a BPF program that needs
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* its insn->imm field to be relocated with actual field info;
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* - type_id - BTF type ID of the "root" (containing) entity of a relocatable
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* field;
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* - access_str_off - offset into corresponding .BTF string section. String
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* itself encodes an accessed field using a sequence of field and array
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* indicies, separated by colon (:). It's conceptually very close to LLVM's
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* getelementptr ([0]) instruction's arguments for identifying offset to
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* a field.
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*
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* Example to provide a better feel.
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*
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* struct sample {
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* int a;
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* struct {
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* int b[10];
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* };
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* };
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*
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* struct sample *s = ...;
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* int x = &s->a; // encoded as "0:0" (a is field #0)
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* int y = &s->b[5]; // encoded as "0:1:0:5" (anon struct is field #1,
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* // b is field #0 inside anon struct, accessing elem #5)
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* int z = &s[10]->b; // encoded as "10:1" (ptr is used as an array)
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*
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* type_id for all relocs in this example will capture BTF type id of
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* `struct sample`.
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*
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* Such relocation is emitted when using __builtin_preserve_access_index()
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* Clang built-in, passing expression that captures field address, e.g.:
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*
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* bpf_probe_read(&dst, sizeof(dst),
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* __builtin_preserve_access_index(&src->a.b.c));
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*
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* In this case Clang will emit field relocation recording necessary data to
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* be able to find offset of embedded `a.b.c` field within `src` struct.
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*
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* [0] https://llvm.org/docs/LangRef.html#getelementptr-instruction
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*/
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struct bpf_field_reloc {
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__u32 insn_off;
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__u32 type_id;
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__u32 access_str_off;
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enum bpf_field_info_kind kind;
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};
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#endif /* __LIBBPF_LIBBPF_INTERNAL_H */
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