Changes in sysfs-kernel-btf

36e68442 - bpf: Load and verify kernel module BTFs

Tue, 10 Nov 2020 01:19:31 +0000

bpf: Load and verify kernel module BTFsAdd kernel module listener that will load/validate and unload module BTF.Module BTFs gets ID generated for them, which makes it possible to iteratethem with existing BTF iteration API. They are given their respective module'snames, which will get reported through GET_OBJ_INFO API. They are also markedas in-kernel BTFs for tooling to distinguish them from user-provided BTFs.Also, similarly to vmlinux BTF, kernel module BTFs are exposed throughsysfs as /sys/kernel/btf/. This is convenient for user-spacetools to inspect module BTF contents and dump their types with existing tools:[vmuser@archvm bpf]$ ls -la /sys/kernel/btftotal 0drwxr-xr-x 2 root root 0 Nov 4 19:46 .drwxr-xr-x 13 root root 0 Nov 4 19:46 .....-r--r--r-- 1 root root 888 Nov 4 19:46 irqbypass-r--r--r-- 1 root root 100225 Nov 4 19:46 kvm-r--r--r-- 1 root root 35401 Nov 4 19:46 kvm_intel-r--r--r-- 1 root root 120 Nov 4 19:46 pcspkr-r--r--r-- 1 root root 399 Nov 4 19:46 serio_raw-r--r--r-- 1 root root 4094095 Nov 4 19:46 vmlinuxSigned-off-by: Andrii Nakryiko Signed-off-by: Alexei Starovoitov Reviewed-by: Greg Kroah-Hartman Link: https://lore.kernel.org/bpf/20201110011932.3201430-5-andrii@kernel.org List of files: /linux-6.15/Documentation/ABI/testing/sysfs-kernel-btf

7fd78568 - btf: rename /sys/kernel/btf/kernel into /sys/kernel/btf/vmlinux

Tue, 13 Aug 2019 18:54:42 +0000

btf: rename /sys/kernel/btf/kernel into /sys/kernel/btf/vmlinuxExpose kernel's BTF under the name vmlinux to be more uniform with usingkernel module names as file names in the future.Fixes: 341dfcf8d78e ("btf: expose BTF info through sysfs")Suggested-by: Daniel Borkmann Signed-off-by: Andrii Nakryiko Signed-off-by: Daniel Borkmann List of files: /linux-6.15/Documentation/ABI/testing/sysfs-kernel-btf

341dfcf8 - btf: expose BTF info through sysfs

Mon, 12 Aug 2019 18:39:47 +0000

btf: expose BTF info through sysfsMake .BTF section allocated and expose its contents through sysfs./sys/kernel/btf directory is created to contain all the BTFs presentinside kernel. Currently there is only kernel's main BTF, represented as/sys/kernel/btf/kernel file. Once kernel modules' BTFs are supported,each module will expose its BTF as /sys/kernel/btf/ file.Current approach relies on a few pieces coming together:1. pahole is used to take almost final vmlinux image (modulo .BTF and kallsyms) and generate .BTF section by converting DWARF info into BTF. This section is not allocated and not mapped to any segment, though, so is not yet accessible from inside kernel at runtime.2. objcopy dumps .BTF contents into binary file and subsequently convert binary file into linkable object file with automatically generated symbols _binary__btf_kernel_bin_start and _binary__btf_kernel_bin_end, pointing to start and end, respectively, of BTF raw data.3. final vmlinux image is generated by linking this object file (and kallsyms, if necessary). sysfs_btf.c then creates /sys/kernel/btf/kernel file and exposes embedded BTF contents through it. This allows, e.g., libbpf and bpftool access BTF info at well-known location, without resorting to searching for vmlinux image on disk (location of which is not standardized and vmlinux image might not be even available in some scenarios, e.g., inside qemu during testing).Alternative approach using .incbin assembler directive to embed BTFcontents directly was attempted but didn't work, because sysfs_proc.o isnot re-compiled during link-vmlinux.sh stage. This is required, though,to update embedded BTF data (initially empty data is embedded, thenpahole generates BTF info and we need to regenerate sysfs_btf.o withupdated contents, but it's too late at that point).If BTF couldn't be generated due to missing or too old pahole,sysfs_btf.c handles that gracefully by detecting that_binary__btf_kernel_bin_start (weak symbol) is 0 and not creating/sys/kernel/btf at all.v2->v3:- added Documentation/ABI/testing/sysfs-kernel-btf (Greg K-H);- created proper kobject (btf_kobj) for btf directory (Greg K-H);- undo v2 change of reusing vmlinux, as it causes extra kallsyms pass due to initially missing __binary__btf_kernel_bin_{start/end} symbols;v1->v2:- allow kallsyms stage to re-use vmlinux generated by gen_btf();Reviewed-by: Greg Kroah-Hartman Signed-off-by: Andrii Nakryiko Signed-off-by: Daniel Borkmann List of files: /linux-6.15/Documentation/ABI/testing/sysfs-kernel-btf