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1c0c7074fe
Add support for another (in addition to existing Kconfig) special kind of externs in BPF code, kernel symbol externs. Such externs allow BPF code to "know" kernel symbol address and either use it for comparisons with kernel data structures (e.g., struct file's f_op pointer, to distinguish different kinds of file), or, with the help of bpf_probe_user_kernel(), to follow pointers and read data from global variables. Kernel symbol addresses are found through /proc/kallsyms, which should be present in the system. Currently, such kernel symbol variables are typeless: they have to be defined as `extern const void <symbol>` and the only operation you can do (in C code) with them is to take its address. Such extern should reside in a special section '.ksyms'. bpf_helpers.h header provides __ksym macro for this. Strong vs weak semantics stays the same as with Kconfig externs. If symbol is not found in /proc/kallsyms, this will be a failure for strong (non-weak) extern, but will be defaulted to 0 for weak externs. If the same symbol is defined multiple times in /proc/kallsyms, then it will be error if any of the associated addresses differs. In that case, address is ambiguous, so libbpf falls on the side of caution, rather than confusing user with randomly chosen address. In the future, once kernel is extended with variables BTF information, such ksym externs will be supported in a typed version, which will allow BPF program to read variable's contents directly, similarly to how it's done for fentry/fexit input arguments. Signed-off-by: Andrii Nakryiko <andriin@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Reviewed-by: Hao Luo <haoluo@google.com> Link: https://lore.kernel.org/bpf/20200619231703.738941-3-andriin@fb.com
80 lines
1.8 KiB
C
80 lines
1.8 KiB
C
/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
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#ifndef __BPF_HELPERS__
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#define __BPF_HELPERS__
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/*
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* Note that bpf programs need to include either
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* vmlinux.h (auto-generated from BTF) or linux/types.h
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* in advance since bpf_helper_defs.h uses such types
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* as __u64.
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*/
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#include "bpf_helper_defs.h"
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#define __uint(name, val) int (*name)[val]
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#define __type(name, val) typeof(val) *name
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#define __array(name, val) typeof(val) *name[]
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/* Helper macro to print out debug messages */
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#define bpf_printk(fmt, ...) \
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({ \
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char ____fmt[] = fmt; \
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bpf_trace_printk(____fmt, sizeof(____fmt), \
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##__VA_ARGS__); \
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})
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/*
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* Helper macro to place programs, maps, license in
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* different sections in elf_bpf file. Section names
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* are interpreted by elf_bpf loader
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*/
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#define SEC(NAME) __attribute__((section(NAME), used))
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#ifndef __always_inline
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#define __always_inline __attribute__((always_inline))
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#endif
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#ifndef __weak
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#define __weak __attribute__((weak))
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#endif
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/*
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* Helper macro to manipulate data structures
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*/
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#ifndef offsetof
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#define offsetof(TYPE, MEMBER) ((size_t)&((TYPE *)0)->MEMBER)
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#endif
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#ifndef container_of
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#define container_of(ptr, type, member) \
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({ \
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void *__mptr = (void *)(ptr); \
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((type *)(__mptr - offsetof(type, member))); \
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})
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#endif
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/*
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* Helper structure used by eBPF C program
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* to describe BPF map attributes to libbpf loader
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*/
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struct bpf_map_def {
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unsigned int type;
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unsigned int key_size;
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unsigned int value_size;
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unsigned int max_entries;
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unsigned int map_flags;
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};
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enum libbpf_pin_type {
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LIBBPF_PIN_NONE,
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/* PIN_BY_NAME: pin maps by name (in /sys/fs/bpf by default) */
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LIBBPF_PIN_BY_NAME,
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};
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enum libbpf_tristate {
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TRI_NO = 0,
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TRI_YES = 1,
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TRI_MODULE = 2,
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};
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#define __kconfig __attribute__((section(".kconfig")))
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#define __ksym __attribute__((section(".ksyms")))
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#endif
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