dwarf_loader: Support btf_type_tag attribute
LLVM patches ([1] for clang, [2] and [3] for BPF backend)
added support for btf_type_tag attributes. The following is
an example:
[$ ~] cat t.c
#define __tag1 __attribute__((btf_type_tag("tag1")))
#define __tag2 __attribute__((btf_type_tag("tag2")))
int __tag1 * __tag1 __tag2 *g __attribute__((section(".data..percpu")));
[$ ~] clang -O2 -g -c t.c
[$ ~] llvm-dwarfdump --debug-info t.o
t.o: file format elf64-x86-64
...
0x0000001e: DW_TAG_variable
DW_AT_name ("g")
DW_AT_type (0x00000033 "int **")
DW_AT_external (true)
DW_AT_decl_file ("/home/yhs/t.c")
DW_AT_decl_line (3)
DW_AT_location (DW_OP_addr 0x0)
0x00000033: DW_TAG_pointer_type
DW_AT_type (0x0000004b "int *")
0x00000038: DW_TAG_LLVM_annotation
DW_AT_name ("btf_type_tag")
DW_AT_const_value ("tag1")
0x00000041: DW_TAG_LLVM_annotation
DW_AT_name ("btf_type_tag")
DW_AT_const_value ("tag2")
0x0000004a: NULL
0x0000004b: DW_TAG_pointer_type
DW_AT_type (0x0000005a "int")
0x00000050: DW_TAG_LLVM_annotation
DW_AT_name ("btf_type_tag")
DW_AT_const_value ("tag1")
0x00000059: NULL
0x0000005a: DW_TAG_base_type
DW_AT_name ("int")
DW_AT_encoding (DW_ATE_signed)
DW_AT_byte_size (0x04)
0x00000061: NULL
From the above example, you can see that DW_TAG_pointer_type may contain
one or more DW_TAG_LLVM_annotation btf_type_tag tags. If
DW_TAG_LLVM_annotation tags are present inside DW_TAG_pointer_type, for
BTF encoding, pahole will need to follow [3] to generate a type chain
like:
var -> ptr -> tag2 -> tag1 -> ptr -> tag1 -> int
This patch implemented dwarf_loader support. If a pointer type contains
DW_TAG_LLVM_annotation tags, a new type btf_type_tag_ptr_type will be
created which will store the pointer tag itself and all
DW_TAG_LLVM_annotation tags. During recoding stage, the type chain will
be formed properly based on the above example.
An option "--skip_encoding_btf_type_tag" is added to disable
this new functionality.
[1] https://reviews.llvm.org/D111199
[2] https://reviews.llvm.org/D113222
[3] https://reviews.llvm.org/D113496
Signed-off-by: Yonghong Song <yhs@fb.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: bpf@vger.kernel.org
Cc: dwarves@vger.kernel.org
Cc: kernel-team@fb.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
3 files changed
