linux/tools/bpf
Andrii Nakryiko 1cf5b23988 bpftool: Apply preserve_access_index attribute to all types in BTF dump
This patch makes structs and unions, emitted through BTF dump, automatically
CO-RE-relocatable (unless disabled with `#define BPF_NO_PRESERVE_ACCESS_INDEX`,
specified before including generated header file).

This effectivaly turns usual bpf_probe_read() call into equivalent of
bpf_core_read(), by automatically applying builtin_preserve_access_index to
any field accesses of types in generated C types header.

This is especially useful for tp_btf/fentry/fexit BPF program types. They
allow direct memory access, so BPF C code just uses straightfoward a->b->c
access pattern to read data from kernel. But without kernel structs marked as
CO-RE relocatable through preserve_access_index attribute, one has to enclose
all the data reads into a special __builtin_preserve_access_index code block,
like so:

__builtin_preserve_access_index(({
    x = p->pid; /* where p is struct task_struct *, for example */
}));

This is very inconvenient and obscures the logic quite a bit. By marking all
auto-generated types with preserve_access_index attribute the above code is
reduced to just a clean and natural `x = p->pid;`.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200113073143.1779940-5-andriin@fb.com
2020-01-13 17:48:13 -08:00
..
bpftool bpftool: Apply preserve_access_index attribute to all types in BTF dump 2020-01-13 17:48:13 -08:00
.gitignore tools: bpf: account for generated feature/ and libbpf/ directories 2019-08-31 00:38:16 +02:00
bpf_asm.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 232 2019-06-19 17:09:06 +02:00
bpf_dbg.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 232 2019-06-19 17:09:06 +02:00
bpf_exp.l bpf: fix cbpf parser bug for octal numbers 2018-06-03 07:46:55 -07:00
bpf_exp.y tools, bpf_asm: Warn when jumps are out of range 2019-11-07 16:01:34 +01:00
bpf_jit_disasm.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 232 2019-06-19 17:09:06 +02:00
Makefile tools, bpf: Fix build for 'make -s tools/bpf O=<dir>' 2019-11-24 16:58:45 -08:00
Makefile.helpers treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00