linux-kernel - pahole issues with Rust DWARF was: Re: [PATCH 1/1] pahole/Rust: Check that we're adding DW_TAG

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Message-ID: <Y+oofL/aJmUjcxIR@kernel.org>
Date:   Mon, 13 Feb 2023 09:09:32 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Martin Rodriguez Reboredo <yakoyoku@...il.com>,
        linux-kernel@...r.kernel.org, Neal Gompa <neal@...pa.dev>,
        Eric Curtin <ecurtin@...hat.com>, bpf@...r.kernel.org,
        rust-for-linux@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>, Yonghong Song <yhs@...com>
Subject: pahole issues with Rust DWARF was: Re: [PATCH 1/1] pahole/Rust:
 Check that we're adding DW_TAG_member sorted by byte offset

Em Fri, Feb 10, 2023 at 05:48:36PM -0300, Arnaldo Carvalho de Melo escreveu:
> I'll go thru the others to see if they are easy (or at least restricted
> to Rust CUs) as this one.

The namespace.o seems to be ok:

⬢[acme@...lbox pahole]$ cat ../pahole-rust-cases/namespace.rs
pub struct S {
    pub a: i32,
}

pub static S: (i32, S) = (42, S { a: 42 });
⬢[acme@...lbox pahole]$

⬢[acme@...lbox pahole]$ pahole --show_private_classes ../pahole-rust-cases/namespace.o
struct S {
	i32                        a __attribute__((__aligned__(4))); /*     0     4 */

	/* size: 4, cachelines: 1, members: 1 */
	/* forced alignments: 1 */
	/* last cacheline: 4 bytes */
} __attribute__((__aligned__(4)));
struct (i32, namespace::S) {
	i32                        __0 __attribute__((__aligned__(4))); /*     0     4 */
	struct S                   __1 __attribute__((__aligned__(4))); /*     4     4 */

	/* size: 8, cachelines: 1, members: 2 */
	/* forced alignments: 2 */
	/* last cacheline: 8 bytes */
} __attribute__((__aligned__(4)));
⬢[acme@...lbox pahole]$

And encoding/decoding BTF for it:

⬢[acme@...lbox pahole]$ cp ../pahole-rust-cases/namespace.o .
⬢[acme@...lbox pahole]$ pahole --btf_encode namespace.o
⬢[acme@...lbox pahole]$ pahole -F btf namespace.o
struct S {
	i32                        a;                    /*     0     4 */

	/* size: 4, cachelines: 1, members: 1 */
	/* last cacheline: 4 bytes */
};
struct (i32, namespace::S) {
	i32                        __0;                  /*     0     4 */
	struct S                   __1;                  /*     4     4 */

	/* size: 8, cachelines: 1, members: 2 */
	/* last cacheline: 8 bytes */
};
⬢[acme@...lbox pahole]$ readelf -SW namespace.o | grep BTF
  [18] .BTF              PROGBITS        0000000000000000 00065c 000089 00      0   0  1
⬢[acme@...lbox pahole]$


The core one needs work:

⬢[acme@...lbox pahole]$ pahole ../pahole-rust-cases/core.o |& head
die__process_class: tag not supported 0x2f (template_type_parameter)!
die__process_class: tag not supported 0x33 (variant_part)!
die__create_new_enumeration: DW_TAG_subprogram (0x2e) @ <0x2fd8d> not handled!
die__create_new_enumeration: DW_TAG_subprogram (0x2e) @ <0x2fdf7> not handled!
die__create_new_enumeration: DW_TAG_subprogram (0x2e) @ <0x2fe61> not handled!
die__create_new_enumeration: DW_TAG_subprogram (0x2e) @ <0x2fecb> not handled!
die__create_new_enumeration: DW_TAG_subprogram (0x2e) @ <0x2ff35> not handled!
die__create_new_enumeration: DW_TAG_subprogram (0x2e) @ <0x2ff9f> not handled!
die__create_new_enumeration: DW_TAG_subprogram (0x2e) @ <0x30009> not handled!
die__create_new_enumeration: DW_TAG_subprogram (0x2e) @ <0x30073> not handled!
⬢[acme@...lbox pahole]$

 <1><90>: Abbrev Number: 7 (DW_TAG_namespace)
    <91>   DW_AT_name        : (indirect string, offset: 0x147): core
 <2><95>: Abbrev Number: 7 (DW_TAG_namespace)
    <96>   DW_AT_name        : (indirect string, offset: 0x14c): str
 <3><9a>: Abbrev Number: 7 (DW_TAG_namespace)
    <9b>   DW_AT_name        : (indirect string, offset: 0x150): iter
 <4><9f>: Abbrev Number: 8 (DW_TAG_structure_type)
    <a0>   DW_AT_name        : (indirect string, offset: 0x2e1): Split<core::str::IsWhitespace>
    <a4>   DW_AT_byte_size   : 64
    <a5>   DW_AT_alignment   : 8
 <5><a6>: Abbrev Number: 9 (DW_TAG_template_type_param)
    <a7>   DW_AT_type        : <0x41fc>
    <ab>   DW_AT_name        : (indirect string, offset: 0x162): P
 <5><af>: Abbrev Number: 4 (DW_TAG_member)
    <b0>   DW_AT_name        : (indirect string, offset: 0x164): __0
    <b4>   DW_AT_type        : <0xbb>
    <b8>   DW_AT_alignment   : 8
    <b9>   DW_AT_data_member_location: 0
 <5><ba>: Abbrev Number: 0
 <4><bb>: Abbrev Number: 8 (DW_TAG_structure_type)
    <bc>   DW_AT_name        : (indirect string, offset: 0x2ba): SplitInternal<core::str::IsWhitespace>
    <c0>   DW_AT_byte_size   : 64
    <c1>   DW_AT_alignment   : 8
 <5><c2>: Abbrev Number: 9 (DW_TAG_template_type_param)
    <c3>   DW_AT_type        : <0x41fc>
    <c7>   DW_AT_name        : (indirect string, offset: 0x162): P

- Arnaldo