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-rw-r--r--Documentation/bpf/btf.rst35
1 files changed, 27 insertions, 8 deletions
diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst
index 7cd7c5415a99..e43c2fdafcd7 100644
--- a/Documentation/bpf/btf.rst
+++ b/Documentation/bpf/btf.rst
@@ -726,8 +726,8 @@ same as the one describe in :ref:`BTF_Type_String`.
4.2 .BTF.ext section
--------------------
-The .BTF.ext section encodes func_info and line_info which needs loader
-manipulation before loading into the kernel.
+The .BTF.ext section encodes func_info, line_info and CO-RE relocations
+which needs loader manipulation before loading into the kernel.
The specification for .BTF.ext section is defined at ``tools/lib/bpf/btf.h``
and ``tools/lib/bpf/btf.c``.
@@ -745,15 +745,20 @@ The current header of .BTF.ext section::
__u32 func_info_len;
__u32 line_info_off;
__u32 line_info_len;
+
+ /* optional part of .BTF.ext header */
+ __u32 core_relo_off;
+ __u32 core_relo_len;
};
It is very similar to .BTF section. Instead of type/string section, it
-contains func_info and line_info section. See :ref:`BPF_Prog_Load` for details
-about func_info and line_info record format.
+contains func_info, line_info and core_relo sub-sections.
+See :ref:`BPF_Prog_Load` for details about func_info and line_info
+record format.
The func_info is organized as below.::
- func_info_rec_size
+ func_info_rec_size /* __u32 value */
btf_ext_info_sec for section #1 /* func_info for section #1 */
btf_ext_info_sec for section #2 /* func_info for section #2 */
...
@@ -773,7 +778,7 @@ Here, num_info must be greater than 0.
The line_info is organized as below.::
- line_info_rec_size
+ line_info_rec_size /* __u32 value */
btf_ext_info_sec for section #1 /* line_info for section #1 */
btf_ext_info_sec for section #2 /* line_info for section #2 */
...
@@ -787,6 +792,20 @@ kernel API, the ``insn_off`` is the instruction offset in the unit of ``struct
bpf_insn``. For ELF API, the ``insn_off`` is the byte offset from the
beginning of section (``btf_ext_info_sec->sec_name_off``).
+The core_relo is organized as below.::
+
+ core_relo_rec_size /* __u32 value */
+ btf_ext_info_sec for section #1 /* core_relo for section #1 */
+ btf_ext_info_sec for section #2 /* core_relo for section #2 */
+
+``core_relo_rec_size`` specifies the size of ``bpf_core_relo``
+structure when .BTF.ext is generated. All ``bpf_core_relo`` structures
+within a single ``btf_ext_info_sec`` describe relocations applied to
+section named by ``btf_ext_info_sec->sec_name_off``.
+
+See :ref:`Documentation/bpf/llvm_reloc.rst <btf-co-re-relocations>`
+for more information on CO-RE relocations.
+
4.2 .BTF_ids section
--------------------
@@ -990,7 +1009,7 @@ format.::
} g2;
int main() { return 0; }
int test() { return 0; }
- -bash-4.4$ clang -c -g -O2 -target bpf t2.c
+ -bash-4.4$ clang -c -g -O2 --target=bpf t2.c
-bash-4.4$ readelf -S t2.o
......
[ 8] .BTF PROGBITS 0000000000000000 00000247
@@ -1000,7 +1019,7 @@ format.::
[10] .rel.BTF.ext REL 0000000000000000 000007e0
0000000000000040 0000000000000010 16 9 8
......
- -bash-4.4$ clang -S -g -O2 -target bpf t2.c
+ -bash-4.4$ clang -S -g -O2 --target=bpf t2.c
-bash-4.4$ cat t2.s
......
.section .BTF,"",@progbits