diff options
| author | Andrii Nakryiko <andrii@kernel.org> | 2022-07-14 00:07:51 -0700 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2022-07-19 09:33:17 -0700 |
| commit | 55d00c37ebc396539b10ab73203bfd5e189c3660 (patch) | |
| tree | 2a63d256373fef7366cc6befa3d7c1a504937c88 /tools/lib/bpf/usdt.bpf.h | |
| parent | 9ff5efdeb0897547cffc275e88d2a55462d9b08e (diff) | |
libbpf: generalize virtual __kconfig externs and use it for USDT
Libbpf supports single virtual __kconfig extern currently: LINUX_KERNEL_VERSION.
LINUX_KERNEL_VERSION isn't coming from /proc/kconfig.gz and is intead
customly filled out by libbpf.
This patch generalizes this approach to support more such virtual
__kconfig externs. One such extern added in this patch is
LINUX_HAS_BPF_COOKIE which is used for BPF-side USDT supporting code in
usdt.bpf.h instead of using CO-RE-based enum detection approach for
detecting bpf_get_attach_cookie() BPF helper. This allows to remove
otherwise not needed CO-RE dependency and keeps user-space and BPF-side
parts of libbpf's USDT support strictly in sync in terms of their
feature detection.
We'll use similar approach for syscall wrapper detection for
BPF_KSYSCALL() BPF-side macro in follow up patch.
Generally, currently libbpf reserves CONFIG_ prefix for Kconfig values
and LINUX_ for virtual libbpf-backed externs. In the future we might
extend the set of prefixes that are supported. This can be done without
any breaking changes, as currently any __kconfig extern with
unrecognized name is rejected.
For LINUX_xxx externs we support the normal "weak rule": if libbpf
doesn't recognize given LINUX_xxx extern but such extern is marked as
__weak, it is not rejected and defaults to zero. This follows
CONFIG_xxx handling logic and will allow BPF applications to
opportunistically use newer libbpf virtual externs without breaking on
older libbpf versions unnecessarily.
Tested-by: Alan Maguire <alan.maguire@oracle.com>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20220714070755.3235561-2-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'tools/lib/bpf/usdt.bpf.h')
| -rw-r--r-- | tools/lib/bpf/usdt.bpf.h | 16 |
1 files changed, 2 insertions, 14 deletions
diff --git a/tools/lib/bpf/usdt.bpf.h b/tools/lib/bpf/usdt.bpf.h index 4181fddb3687..4f2adc0bd6ca 100644 --- a/tools/lib/bpf/usdt.bpf.h +++ b/tools/lib/bpf/usdt.bpf.h @@ -6,7 +6,6 @@ #include <linux/errno.h> #include <bpf/bpf_helpers.h> #include <bpf/bpf_tracing.h> -#include <bpf/bpf_core_read.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 @@ -30,14 +29,6 @@ #ifndef BPF_USDT_MAX_IP_CNT #define BPF_USDT_MAX_IP_CNT (4 * BPF_USDT_MAX_SPEC_CNT) #endif -/* We use BPF CO-RE to detect support for BPF cookie from BPF side. This is - * the only dependency on CO-RE, so if it's undesirable, user can override - * BPF_USDT_HAS_BPF_COOKIE to specify whether to BPF cookie is supported or not. - */ -#ifndef BPF_USDT_HAS_BPF_COOKIE -#define BPF_USDT_HAS_BPF_COOKIE \ - bpf_core_enum_value_exists(enum bpf_func_id___usdt, BPF_FUNC_get_attach_cookie___usdt) -#endif enum __bpf_usdt_arg_type { BPF_USDT_ARG_CONST, @@ -83,15 +74,12 @@ struct { __type(value, __u32); } __bpf_usdt_ip_to_spec_id SEC(".maps") __weak; -/* don't rely on user's BPF code to have latest definition of bpf_func_id */ -enum bpf_func_id___usdt { - BPF_FUNC_get_attach_cookie___usdt = 0xBAD, /* value doesn't matter */ -}; +extern const _Bool LINUX_HAS_BPF_COOKIE __kconfig; static __always_inline int __bpf_usdt_spec_id(struct pt_regs *ctx) { - if (!BPF_USDT_HAS_BPF_COOKIE) { + if (!LINUX_HAS_BPF_COOKIE) { long ip = PT_REGS_IP(ctx); int *spec_id_ptr; |