commit | 18922504c3366d5738322466a53c172c025097a0 | [log] [tgz] |
---|---|---|
author | Dave Marchevsky <davemarchevsky@fb.com> | Fri Sep 17 11:29:06 2021 -0700 |
committer | Andrii Nakryiko <andrii.nakryiko@gmail.com> | Wed Sep 29 12:05:46 2021 -0700 |
tree | fde80c52144588514b94dc3694c3c58ba0bf3246 | |
parent | 029273039d466f4629213dd281800541cf93c9d3 [diff] |
libbpf: Modify bpf_printk to choose helper based on arg count Instead of being a thin wrapper which calls into bpf_trace_printk, libbpf's bpf_printk convenience macro now chooses between bpf_trace_printk and bpf_trace_vprintk. If the arg count (excluding format string) is >3, use bpf_trace_vprintk, otherwise use the older helper. The motivation behind this added complexity - instead of migrating entirely to bpf_trace_vprintk - is to maintain good developer experience for users compiling against new libbpf but running on older kernels. Users who are passing <=3 args to bpf_printk will see no change in their bytecode. __bpf_vprintk functions similarly to BPF_SEQ_PRINTF and BPF_SNPRINTF macros elsewhere in the file - it allows use of bpf_trace_vprintk without manual conversion of varargs to u64 array. Previous implementation of bpf_printk macro is moved to __bpf_printk for use by the new implementation. This does change behavior of bpf_printk calls with >3 args in the "new libbpf, old kernels" scenario. Before this patch, attempting to use 4 args to bpf_printk results in a compile-time error. After this patch, using bpf_printk with 4 args results in a trace_vprintk helper call being emitted and a load-time failure on older kernels. Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20210917182911.2426606-5-davemarchevsky@fb.com
This is a mirror of bpf-next Linux source tree's tools/lib/bpf
directory plus its supporting header files.
All the gory details of syncing can be found in scripts/sync-kernel.sh
script.
Some header files in this repo (include/linux/*.h
) are reduced versions of their counterpart files at bpf-next's tools/include/linux/*.h
to make compilation successful.
Please check out libbpf-bootstrap and the companion blog post for the examples of building BPF applications with libbpf. libbpf-tools are also a good source of the real-world libbpf-based tracing tools.
All general BPF questions, including kernel functionality, libbpf APIs and their application, should be sent to bpf@vger.kernel.org mailing list. You can subscribe to it here and search its archive here. Please search the archive before asking new questions. It very well might be that this was already addressed or answered before.
bpf@vger.kernel.org is monitored by many more people and they will happily try to help you with whatever issue you have. This repository's PRs and issues should be opened only for dealing with issues pertaining to specific way this libbpf mirror repo is set up and organized.
libelf is an internal dependency of libbpf and thus it is required to link against and must be installed on the system for applications to work. pkg-config is used by default to find libelf, and the program called can be overridden with PKG_CONFIG
.
If using pkg-config
at build time is not desired, it can be disabled by setting NO_PKG_CONFIG=1
when calling make.
To build both static libbpf.a and shared libbpf.so:
$ cd src
$ make
To build only static libbpf.a library in directory build/ and install them together with libbpf headers in a staging directory root/:
$ cd src $ mkdir build root $ BUILD_STATIC_ONLY=y OBJDIR=build DESTDIR=root make install
To build both static libbpf.a and shared libbpf.so against a custom libelf dependency installed in /build/root/ and install them together with libbpf headers in a build directory /build/root/:
$ cd src $ PKG_CONFIG_PATH=/build/root/lib64/pkgconfig DESTDIR=/build/root make install
Distributions packaging libbpf from this mirror:
Benefits of packaging from the mirror over packaging from kernel sources:
Package dependencies of libbpf, package names may vary across distros:
Libbpf supports building BPF CO-RE-enabled applications, which, in contrast to BCC, do not require Clang/LLVM runtime being deployed to target servers and doesn't rely on kernel-devel headers being available.
It does rely on kernel to be built with BTF type information, though. Some major Linux distributions come with kernel BTF already built in:
If your kernel doesn‘t come with BTF built-in, you’ll need to build custom kernel. You'll need:
pahole
1.16+ tool (part of dwarves
package), which performs DWARF to BTF conversion;CONFIG_DEBUG_INFO_BTF=y
option;/sys/kernel/btf/vmlinux
file:$ ls -la /sys/kernel/btf/vmlinux -r--r--r--. 1 root root 3541561 Jun 2 18:16 /sys/kernel/btf/vmlinux
To develop and build BPF programs, you'll need Clang/LLVM 10+. The following distributions have Clang/LLVM 10+ packaged by default:
Otherwise, please make sure to update it on your system.
The following resources are useful to understand what BPF CO-RE is and how to use it:
This work is dual-licensed under BSD 2-clause license and GNU LGPL v2.1 license. You can choose between one of them if you use this work.
SPDX-License-Identifier: BSD-2-Clause OR LGPL-2.1