On 2/10/22 4:31 PM, Yonghong Song wrote:
On 2/10/22 3:24 PM, Kumar Kartikeya Dwivedi wrote:
Hello,
I was trying to use BTF type tags, but I noticed that when I apply it
to a
non-builtin type, it isn't emitted in the 'PTR' -> 'TYPE_TAG' ->
<TYPE> chain.
Consider the following two cases:
; cat tag_good.c
#define __btf_id __attribute__((btf_type_tag("btf_id")))
#define __ref __attribute__((btf_type_tag("ref")))
struct map_value {
long __btf_id __ref *ptr;
};
void func(struct map_value *, long *);
int main(void)
{
struct map_value v = {};
func(&v, v.ptr);
}
; cat tag_bad.c
#define __btf_id __attribute__((btf_type_tag("btf_id")))
#define __ref __attribute__((btf_type_tag("ref")))
struct foo {
int i;
};
struct map_value {
struct foo __btf_id __ref *ptr;
};
void func(struct map_value *, struct foo *);
int main(void)
{
struct map_value v = {};
func(&v, v.ptr);
}
--
In the first case, it is applied to a long, in the second, it is
applied to
struct foo.
For the first case, we see:
[1] FUNC_PROTO '(anon)' ret_type_id=2 vlen=0
[2] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
[3] FUNC 'main' type_id=1 linkage=global
[4] FUNC_PROTO '(anon)' ret_type_id=0 vlen=2
'(anon)' type_id=5
'(anon)' type_id=11
[5] PTR '(anon)' type_id=6
[6] STRUCT 'map_value' size=8 vlen=1
'ptr' type_id=9 bits_offset=0
[7] TYPE_TAG 'btf_id' type_id=10
[8] TYPE_TAG 'ref' type_id=7
[9] PTR '(anon)' type_id=8
[10] INT 'long' size=8 bits_offset=0 nr_bits=64 encoding=SIGNED
[11] PTR '(anon)' type_id=10
[12] FUNC 'func' type_id=4 linkage=extern
For the second, there is no TYPE_TAG:
; ../linux/tools/bpf/bpftool/bpftool btf dump file tag_bad.o
[1] FUNC_PROTO '(anon)' ret_type_id=2 vlen=0
[2] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
[3] FUNC 'main' type_id=1 linkage=global
[4] FUNC_PROTO '(anon)' ret_type_id=0 vlen=2
'(anon)' type_id=5
'(anon)' type_id=8
[5] PTR '(anon)' type_id=6
[6] STRUCT 'map_value' size=8 vlen=1
'ptr' type_id=7 bits_offset=0
[7] PTR '(anon)' type_id=9
[8] PTR '(anon)' type_id=9
[9] STRUCT 'foo' size=4 vlen=1
'i' type_id=2 bits_offset=0
[10] FUNC 'func' type_id=4 linkage=extern
--
Is there anything I am missing here? When I do llvm-dwarfdump for
both, I see
that the tag annotation is present for both:
Thanks for trying and reporting! This should be a llvm bpf backend bug.
Will fix it soon.
The issue is fixed in https://reviews.llvm.org/D119799 and
the patch is merged in llvm-project main branch.
Could you take a look again? Thanks!
For the good case:
0x00000067: DW_TAG_pointer_type
DW_AT_type (0x00000073 "long")
0x0000006c: DW_TAG_unknown_6000
DW_AT_name ("btf_type_tag")
DW_AT_const_value ("btf_id")
BTW, if you use the same llvm-dwarfdump from 15.0.0,
$ llvm-dwarfdump --version
LLVM
(http://llvm.org/
):
LLVM version 15.0.0git
Optimized build with assertions.
Default target: x86_64-unknown-linux-gnu
Host CPU: skylake-avx512
You should see
0x0000006c: DW_TAG_LLVM_annotation
DW_AT_name ("btf_type_tag")
DW_AT_const_value ("btf_id")
instead of
DW_TAG_unknown_6000
0x0000006f: DW_TAG_unknown_6000
DW_AT_name ("btf_type_tag")
DW_AT_const_value ("ref")
For the bad case:
0x00000067: DW_TAG_pointer_type
DW_AT_type (0x00000073 "foo")
0x0000006c: DW_TAG_unknown_6000
DW_AT_name ("btf_type_tag")
DW_AT_const_value ("btf_id")
0x0000006f: DW_TAG_unknown_6000
DW_AT_name ("btf_type_tag")
DW_AT_const_value ("ref")
My clang version is a very recent compile:
clang version 15.0.0 (https://github.com/llvm/llvm-project.git
9e08e9298059651e4f42eb608c3de9d4ad8004b2)
Thanks
--
Kartikeya
