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- /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
- /* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
- #ifndef __USDT_BPF_H__
- #define __USDT_BPF_H__
- #include <linux/errno.h>
- #include <bpf/bpf_helpers.h>
- #include <bpf/bpf_tracing.h>
- /* Below types and maps are internal implementation details of libbpf's USDT
- * support and are subjects to change. Also, bpf_usdt_xxx() API helpers should
- * be considered an unstable API as well and might be adjusted based on user
- * feedback from using libbpf's USDT support in production.
- */
- /* User can override BPF_USDT_MAX_SPEC_CNT to change default size of internal
- * map that keeps track of USDT argument specifications. This might be
- * necessary if there are a lot of USDT attachments.
- */
- #ifndef BPF_USDT_MAX_SPEC_CNT
- #define BPF_USDT_MAX_SPEC_CNT 256
- #endif
- /* User can override BPF_USDT_MAX_IP_CNT to change default size of internal
- * map that keeps track of IP (memory address) mapping to USDT argument
- * specification.
- * Note, if kernel supports BPF cookies, this map is not used and could be
- * resized all the way to 1 to save a bit of memory.
- */
- #ifndef BPF_USDT_MAX_IP_CNT
- #define BPF_USDT_MAX_IP_CNT (4 * BPF_USDT_MAX_SPEC_CNT)
- #endif
- enum __bpf_usdt_arg_type {
- BPF_USDT_ARG_CONST,
- BPF_USDT_ARG_REG,
- BPF_USDT_ARG_REG_DEREF,
- };
- struct __bpf_usdt_arg_spec {
- /* u64 scalar interpreted depending on arg_type, see below */
- __u64 val_off;
- /* arg location case, see bpf_udst_arg() for details */
- enum __bpf_usdt_arg_type arg_type;
- /* offset of referenced register within struct pt_regs */
- short reg_off;
- /* whether arg should be interpreted as signed value */
- bool arg_signed;
- /* number of bits that need to be cleared and, optionally,
- * sign-extended to cast arguments that are 1, 2, or 4 bytes
- * long into final 8-byte u64/s64 value returned to user
- */
- char arg_bitshift;
- };
- /* should match USDT_MAX_ARG_CNT in usdt.c exactly */
- #define BPF_USDT_MAX_ARG_CNT 12
- struct __bpf_usdt_spec {
- struct __bpf_usdt_arg_spec args[BPF_USDT_MAX_ARG_CNT];
- __u64 usdt_cookie;
- short arg_cnt;
- };
- struct {
- __uint(type, BPF_MAP_TYPE_ARRAY);
- __uint(max_entries, BPF_USDT_MAX_SPEC_CNT);
- __type(key, int);
- __type(value, struct __bpf_usdt_spec);
- } __bpf_usdt_specs SEC(".maps") __weak;
- struct {
- __uint(type, BPF_MAP_TYPE_HASH);
- __uint(max_entries, BPF_USDT_MAX_IP_CNT);
- __type(key, long);
- __type(value, __u32);
- } __bpf_usdt_ip_to_spec_id SEC(".maps") __weak;
- extern const _Bool LINUX_HAS_BPF_COOKIE __kconfig;
- static __always_inline
- int __bpf_usdt_spec_id(struct pt_regs *ctx)
- {
- if (!LINUX_HAS_BPF_COOKIE) {
- long ip = PT_REGS_IP(ctx);
- int *spec_id_ptr;
- spec_id_ptr = bpf_map_lookup_elem(&__bpf_usdt_ip_to_spec_id, &ip);
- return spec_id_ptr ? *spec_id_ptr : -ESRCH;
- }
- return bpf_get_attach_cookie(ctx);
- }
- /* Return number of USDT arguments defined for currently traced USDT. */
- __weak __hidden
- int bpf_usdt_arg_cnt(struct pt_regs *ctx)
- {
- struct __bpf_usdt_spec *spec;
- int spec_id;
- spec_id = __bpf_usdt_spec_id(ctx);
- if (spec_id < 0)
- return -ESRCH;
- spec = bpf_map_lookup_elem(&__bpf_usdt_specs, &spec_id);
- if (!spec)
- return -ESRCH;
- return spec->arg_cnt;
- }
- /* Fetch USDT argument #*arg_num* (zero-indexed) and put its value into *res.
- * Returns 0 on success; negative error, otherwise.
- * On error *res is guaranteed to be set to zero.
- */
- __weak __hidden
- int bpf_usdt_arg(struct pt_regs *ctx, __u64 arg_num, long *res)
- {
- struct __bpf_usdt_spec *spec;
- struct __bpf_usdt_arg_spec *arg_spec;
- unsigned long val;
- int err, spec_id;
- *res = 0;
- spec_id = __bpf_usdt_spec_id(ctx);
- if (spec_id < 0)
- return -ESRCH;
- spec = bpf_map_lookup_elem(&__bpf_usdt_specs, &spec_id);
- if (!spec)
- return -ESRCH;
- if (arg_num >= BPF_USDT_MAX_ARG_CNT || arg_num >= spec->arg_cnt)
- return -ENOENT;
- arg_spec = &spec->args[arg_num];
- switch (arg_spec->arg_type) {
- case BPF_USDT_ARG_CONST:
- /* Arg is just a constant ("-4@$-9" in USDT arg spec).
- * value is recorded in arg_spec->val_off directly.
- */
- val = arg_spec->val_off;
- break;
- case BPF_USDT_ARG_REG:
- /* Arg is in a register (e.g, "8@%rax" in USDT arg spec),
- * so we read the contents of that register directly from
- * struct pt_regs. To keep things simple user-space parts
- * record offsetof(struct pt_regs, <regname>) in arg_spec->reg_off.
- */
- err = bpf_probe_read_kernel(&val, sizeof(val), (void *)ctx + arg_spec->reg_off);
- if (err)
- return err;
- break;
- case BPF_USDT_ARG_REG_DEREF:
- /* Arg is in memory addressed by register, plus some offset
- * (e.g., "-4@-1204(%rbp)" in USDT arg spec). Register is
- * identified like with BPF_USDT_ARG_REG case, and the offset
- * is in arg_spec->val_off. We first fetch register contents
- * from pt_regs, then do another user-space probe read to
- * fetch argument value itself.
- */
- err = bpf_probe_read_kernel(&val, sizeof(val), (void *)ctx + arg_spec->reg_off);
- if (err)
- return err;
- err = bpf_probe_read_user(&val, sizeof(val), (void *)val + arg_spec->val_off);
- if (err)
- return err;
- #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
- val >>= arg_spec->arg_bitshift;
- #endif
- break;
- default:
- return -EINVAL;
- }
- /* cast arg from 1, 2, or 4 bytes to final 8 byte size clearing
- * necessary upper arg_bitshift bits, with sign extension if argument
- * is signed
- */
- val <<= arg_spec->arg_bitshift;
- if (arg_spec->arg_signed)
- val = ((long)val) >> arg_spec->arg_bitshift;
- else
- val = val >> arg_spec->arg_bitshift;
- *res = val;
- return 0;
- }
- /* Retrieve user-specified cookie value provided during attach as
- * bpf_usdt_opts.usdt_cookie. This serves the same purpose as BPF cookie
- * returned by bpf_get_attach_cookie(). Libbpf's support for USDT is itself
- * utilizing BPF cookies internally, so user can't use BPF cookie directly
- * for USDT programs and has to use bpf_usdt_cookie() API instead.
- */
- __weak __hidden
- long bpf_usdt_cookie(struct pt_regs *ctx)
- {
- struct __bpf_usdt_spec *spec;
- int spec_id;
- spec_id = __bpf_usdt_spec_id(ctx);
- if (spec_id < 0)
- return 0;
- spec = bpf_map_lookup_elem(&__bpf_usdt_specs, &spec_id);
- if (!spec)
- return 0;
- return spec->usdt_cookie;
- }
- /* we rely on ___bpf_apply() and ___bpf_narg() macros already defined in bpf_tracing.h */
- #define ___bpf_usdt_args0() ctx
- #define ___bpf_usdt_args1(x) ___bpf_usdt_args0(), ({ long _x; bpf_usdt_arg(ctx, 0, &_x); (void *)_x; })
- #define ___bpf_usdt_args2(x, args...) ___bpf_usdt_args1(args), ({ long _x; bpf_usdt_arg(ctx, 1, &_x); (void *)_x; })
- #define ___bpf_usdt_args3(x, args...) ___bpf_usdt_args2(args), ({ long _x; bpf_usdt_arg(ctx, 2, &_x); (void *)_x; })
- #define ___bpf_usdt_args4(x, args...) ___bpf_usdt_args3(args), ({ long _x; bpf_usdt_arg(ctx, 3, &_x); (void *)_x; })
- #define ___bpf_usdt_args5(x, args...) ___bpf_usdt_args4(args), ({ long _x; bpf_usdt_arg(ctx, 4, &_x); (void *)_x; })
- #define ___bpf_usdt_args6(x, args...) ___bpf_usdt_args5(args), ({ long _x; bpf_usdt_arg(ctx, 5, &_x); (void *)_x; })
- #define ___bpf_usdt_args7(x, args...) ___bpf_usdt_args6(args), ({ long _x; bpf_usdt_arg(ctx, 6, &_x); (void *)_x; })
- #define ___bpf_usdt_args8(x, args...) ___bpf_usdt_args7(args), ({ long _x; bpf_usdt_arg(ctx, 7, &_x); (void *)_x; })
- #define ___bpf_usdt_args9(x, args...) ___bpf_usdt_args8(args), ({ long _x; bpf_usdt_arg(ctx, 8, &_x); (void *)_x; })
- #define ___bpf_usdt_args10(x, args...) ___bpf_usdt_args9(args), ({ long _x; bpf_usdt_arg(ctx, 9, &_x); (void *)_x; })
- #define ___bpf_usdt_args11(x, args...) ___bpf_usdt_args10(args), ({ long _x; bpf_usdt_arg(ctx, 10, &_x); (void *)_x; })
- #define ___bpf_usdt_args12(x, args...) ___bpf_usdt_args11(args), ({ long _x; bpf_usdt_arg(ctx, 11, &_x); (void *)_x; })
- #define ___bpf_usdt_args(args...) ___bpf_apply(___bpf_usdt_args, ___bpf_narg(args))(args)
- /*
- * BPF_USDT serves the same purpose for USDT handlers as BPF_PROG for
- * tp_btf/fentry/fexit BPF programs and BPF_KPROBE for kprobes.
- * Original struct pt_regs * context is preserved as 'ctx' argument.
- */
- #define BPF_USDT(name, args...) \
- name(struct pt_regs *ctx); \
- static __always_inline typeof(name(0)) \
- ____##name(struct pt_regs *ctx, ##args); \
- typeof(name(0)) name(struct pt_regs *ctx) \
- { \
- _Pragma("GCC diagnostic push") \
- _Pragma("GCC diagnostic ignored \"-Wint-conversion\"") \
- return ____##name(___bpf_usdt_args(args)); \
- _Pragma("GCC diagnostic pop") \
- } \
- static __always_inline typeof(name(0)) \
- ____##name(struct pt_regs *ctx, ##args)
- #endif /* __USDT_BPF_H__ */
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