core: Check that we're adding DW_TAG_member sorted by byte offset
Rust reorder struct fields and pahole assumes them to be in order, as is
the case for languages like C and C++, etc. So when adding a
DW_TAG_member, add it in order.
Using: https://github.com/Rust-for-Linux/pahole-rust-cases/blob/main/inverted.o
Before:
$ pahole --show_private_classes ../pahole-rust-cases/inverted.o
struct S {
/* XXX 4 bytes hole, try to pack */
bool a __attribute__((__aligned__(1))); /* 4 1 */
/* XXX 65531 bytes hole, try to pack */
/* Bitfield combined with previous fields */
u32 b __attribute__((__aligned__(4))); /* 0 4 */
/* size: 8, cachelines: 1, members: 2 */
/* sum members: 5, holes: 2, sum holes: 65535 */
/* padding: 4 */
/* forced alignments: 2, forced holes: 2, sum forced holes: 65535 */
/* last cacheline: 8 bytes */
/* BRAIN FART ALERT! 8 bytes != 5 (member bytes) + 0 (member bits) + 65535 (byte holes) + 0 (bit holes), diff = -524288 bits */
} __attribute__((__aligned__(4)));
$
After:
$ readelf -wi ../pahole-rust-cases/inverted.o | grep DW_TAG_compile_unit -A9
<0><b>: Abbrev Number: 1 (DW_TAG_compile_unit)
<c> DW_AT_producer : (indirect string, offset: 0x0): clang LLVM (rustc version 1.60.0 (7737e0b5c 2022-04-04))
<10> DW_AT_language : 28 (Rust)
<12> DW_AT_name : (indirect string, offset: 0x39): inverted.rs/@/inverted.c4dda47b-cgu.0
<16> DW_AT_stmt_list : 0x0
<1a> DW_AT_comp_dir : (indirect string, offset: 0x5f): /root/pahole-rust
<1e> DW_AT_GNU_pubnames: 1
<1e> DW_AT_low_pc : 0x0
<26> DW_AT_high_pc : 0x62
<1><2a>: Abbrev Number: 2 (DW_TAG_namespace)
$ pahole --show_private_classes ../pahole-rust-cases/inverted.o
struct S {
u32 b __attribute__((__aligned__(4))); /* 0 4 */
bool a __attribute__((__aligned__(1))); /* 4 1 */
/* size: 8, cachelines: 1, members: 2 */
/* padding: 3 */
/* forced alignments: 2 */
/* last cacheline: 8 bytes */
} __attribute__((__aligned__(4)));
$
$ cp ../pahole-rust-cases/inverted.o .
$ pahole --btf_encode inverted.o
$ readelf -SW inverted.o | grep -i BTF
[26] .BTF PROGBITS 0000000000000000 000922 00006c 00 0 0 1
$
$ pahole -F btf inverted.o
struct S {
u32 b; /* 0 4 */
bool a; /* 4 1 */
/* size: 8, cachelines: 1, members: 2 */
/* padding: 3 */
/* last cacheline: 8 bytes */
};
$
Reported-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Eric Curtin <ecurtin@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Cc: Neal Gompa <neal@gompa.dev>
Cc: Yonghong Song <yhs@fb.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
1 file changed
