2d91c46d1a
Perform the same virtual address to file offset translation that libbpf is doing for executable ELF binaries also for shared libraries. Currently libbpf is making a simplifying and sometimes wrong assumption that for shared libraries relative virtual addresses inside ELF are always equal to file offsets. Unfortunately, this is not always the case with LLVM's lld linker, which now by default generates quite more complicated ELF segments layout. E.g., for liburandom_read.so from selftests/bpf, here's an excerpt from readelf output listing ELF segments (a.k.a. program headers): Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align PHDR 0x000040 0x0000000000000040 0x0000000000000040 0x0001f8 0x0001f8 R 0x8 LOAD 0x000000 0x0000000000000000 0x0000000000000000 0x0005e4 0x0005e4 R 0x1000 LOAD 0x0005f0 0x00000000000015f0 0x00000000000015f0 0x000160 0x000160 R E 0x1000 LOAD 0x000750 0x0000000000002750 0x0000000000002750 0x000210 0x000210 RW 0x1000 LOAD 0x000960 0x0000000000003960 0x0000000000003960 0x000028 0x000029 RW 0x1000 Compare that to what is generated by GNU ld (or LLVM lld's with extra -znoseparate-code argument which disables this cleverness in the name of file size reduction): Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align LOAD 0x000000 0x0000000000000000 0x0000000000000000 0x000550 0x000550 R 0x1000 LOAD 0x001000 0x0000000000001000 0x0000000000001000 0x000131 0x000131 R E 0x1000 LOAD 0x002000 0x0000000000002000 0x0000000000002000 0x0000ac 0x0000ac R 0x1000 LOAD 0x002dc0 0x0000000000003dc0 0x0000000000003dc0 0x000262 0x000268 RW 0x1000 You can see from the first example above that for executable (Flg == "R E") PT_LOAD segment (LOAD #2), Offset doesn't match VirtAddr columns. And it does in the second case (GNU ld output). This is important because all the addresses, including USDT specs, operate in a virtual address space, while kernel is expecting file offsets when performing uprobe attach. So such mismatches have to be properly taken care of and compensated by libbpf, which is what this patch is fixing. Also patch clarifies few function and variable names, as well as updates comments to reflect this important distinction (virtaddr vs file offset) and to ephasize that shared libraries are not all that different from executables in this regard. This patch also changes selftests/bpf Makefile to force urand_read and liburand_read.so to be built with Clang and LLVM's lld (and explicitly request this ELF file size optimization through -znoseparate-code linker parameter) to validate libbpf logic and ensure regressions don't happen in the future. I've bundled these selftests changes together with libbpf changes to keep the above description tied with both libbpf and selftests changes. Fixes: 74cc6311cec9 ("libbpf: Add USDT notes parsing and resolution logic") Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/bpf/20220616055543.3285835-1-andrii@kernel.org
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.
BPF/libbpf usage and questions
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.
See also "BPF CO-RE reference guide" for the coverage of practical aspects of building BPF CO-RE applications and "BPF CO-RE" for general introduction into BPF portability issues and BPF CO-RE origins.
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.
Build
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
BPF CO-RE (Compile Once – Run Everywhere)
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:
- Fedora 31+
- RHEL 8.2+
- OpenSUSE Tumbleweed (in the next release, as of 2020-06-04)
- Arch Linux (from kernel 5.7.1.arch1-1)
- Manjaro (from kernel 5.4 if compiled after 2021-06-18)
- Ubuntu 20.10
- Debian 11 (amd64/arm64)
If your kernel doesn't come with BTF built-in, you'll need to build custom kernel. You'll need:
pahole1.16+ tool (part ofdwarvespackage), which performs DWARF to BTF conversion;- kernel built with
CONFIG_DEBUG_INFO_BTF=yoption; - you can check if your kernel has BTF built-in by looking for
/sys/kernel/btf/vmlinuxfile:
$ 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:
- Fedora 32+
- Ubuntu 20.04+
- Arch Linux
- Ubuntu 20.10 (LLVM 11)
- Debian 11 (LLVM 11)
- Alpine 3.13+
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:
- BPF CO-RE reference guide
- BPF Portability and CO-RE
- HOWTO: BCC to libbpf conversion
- libbpf-tools in BCC repo contain lots of real-world tools converted from BCC to BPF CO-RE. Consider converting some more to both contribute to the BPF community and gain some more experience with it.
Distributions
Distributions packaging libbpf from this mirror:
Benefits of packaging from the mirror over packaging from kernel sources:
- Consistent versioning across distributions.
- No ties to any specific kernel, transparent handling of older kernels. Libbpf is designed to be kernel-agnostic and work across multitude of kernel versions. It has built-in mechanisms to gracefully handle older kernels, that are missing some of the features, by working around or gracefully degrading functionality. Thus libbpf is not tied to a specific kernel version and can/should be packaged and versioned independently.
- Continuous integration testing via TravisCI.
- Static code analysis via LGTM and Coverity.
Package dependencies of libbpf, package names may vary across distros:
- zlib
- libelf
License
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