From: Leon Hwang <leon.hwang@linux.dev>
To: Tiezhu Yang <yangtiezhu@loongson.cn>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Eduard Zingerman <eddyz87@gmail.com>,
Kumar Kartikeya Dwivedi <memxor@gmail.com>,
Martin KaFai Lau <martin.lau@linux.dev>,
Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
Jiri Olsa <jolsa@kernel.org>,
Emil Tsalapatis <emil@etsalapatis.com>,
KaFai Wan <kafai.wan@linux.dev>
Cc: bpf@vger.kernel.org, loongarch@lists.linux.dev
Subject: Re: [PATCH bpf-next v5] bpf: Reject programs with inlined helpers if JIT is unavailable
Date: Thu, 2 Jul 2026 11:17:06 +0800 [thread overview]
Message-ID: <3fe115fd-8df8-4bf0-805b-2d0c2c40fdf5@linux.dev> (raw)
In-Reply-To: <20260702022108.17693-1-yangtiezhu@loongson.cn>
On 2/7/26 10:21, Tiezhu Yang wrote:
[...]
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index ba09795e0bfd..463fae6a5c33 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1865,8 +1865,9 @@ struct bpf_prog_aux {
>
> struct bpf_prog {
> u16 pages; /* Number of allocated pages */
> - u16 jited:1, /* Is our filter JIT'ed? */
> + u32 jited:1, /* Is our filter JIT'ed? */
> jit_requested:1,/* archs need to JIT the prog */
> + jit_required:1, /* program strictly requires JIT compiler */
Looks good to put jit_required together with jit_requested.
However, 'u16 -> u32' changes the layout of struct bpf_prog.
Before the change, pahole -C bpf_prog ./vmlinux
struct bpf_prog {
u16 pages; /* 0 2 */
u16 jited:1; /* 2: 0 2 */
u16 jit_requested:1; /* 2: 1 2 */
u16 gpl_compatible:1; /* 2: 2 2 */
u16 cb_access:1; /* 2: 3 2 */
u16 dst_needed:1; /* 2: 4 2 */
u16 blinding_requested:1; /* 2: 5 2 */
u16 blinded:1; /* 2: 6 2 */
u16 is_func:1; /* 2: 7 2 */
u16 kprobe_override:1; /* 2: 8 2 */
u16 has_callchain_buf:1; /* 2: 9 2 */
u16 enforce_expected_attach_type:1; /* 2:10
2 */
u16 call_get_stack:1; /* 2:11 2 */
u16 call_get_func_ip:1; /* 2:12 2 */
u16 call_session_cookie:1; /* 2:13 2 */
u16 tstamp_type_access:1; /* 2:14 2 */
u16 sleepable:1; /* 2:15 2 */
enum bpf_prog_type type; /* 4 4 */
enum bpf_attach_type expected_attach_type; /* 8 4 */
u32 len; /* 12 4 */
u32 jited_len; /* 16 4 */
union {
u8 digest[32]; /* 20 32 */
u8 tag[8]; /* 20 8 */
}; /* 20 32 */
/* XXX 4 bytes hole, try to pack */
struct bpf_prog_stats * stats; /* 56 8 */
/* --- cacheline 1 boundary (64 bytes) --- */
u8 * active; /* 64 8 */
unsigned int (*bpf_func)(const void *, const struct
bpf_insn *); /* 72 8 */
struct bpf_prog_aux * aux; /* 80 8 */
struct sock_fprog_kern * orig_prog; /* 88 8 */
union {
struct {
struct {
} __empty_insns; /* 96 0 */
struct sock_filter insns[0]; /* 96 0 */
}; /* 96 0 */
struct {
struct {
} __empty_insnsi; /* 96 0 */
struct bpf_insn insnsi[0]; /* 96 0 */
}; /* 96 0 */
}; /* 96 0 */
/* size: 96, cachelines: 2, members: 28 */
/* sum members: 90, holes: 1, sum holes: 4 */
/* sum bitfield members: 16 bits (2 bytes) */
/* last cacheline: 32 bytes */
};
After the change, pahole -C bpf_prog ./vmlinux
struct bpf_prog {
u16 pages; /* 0 2 */
/* Bitfield combined with previous fields */
u32 jited:1; /* 0:16 4 */
u32 jit_requested:1; /* 0:17 4 */
u32 jit_required:1; /* 0:18 4 */
u32 gpl_compatible:1; /* 0:19 4 */
u32 cb_access:1; /* 0:20 4 */
u32 dst_needed:1; /* 0:21 4 */
u32 blinding_requested:1; /* 0:22 4 */
u32 blinded:1; /* 0:23 4 */
u32 is_func:1; /* 0:24 4 */
u32 kprobe_override:1; /* 0:25 4 */
u32 has_callchain_buf:1; /* 0:26 4 */
u32 enforce_expected_attach_type:1; /* 0:27
4 */
u32 call_get_stack:1; /* 0:28 4 */
u32 call_get_func_ip:1; /* 0:29 4 */
u32 call_session_cookie:1; /* 0:30 4 */
u32 tstamp_type_access:1; /* 0:31 4 */
u32 sleepable:1; /* 4: 0 4 */
/* XXX 31 bits hole, try to pack */
enum bpf_prog_type type; /* 8 4 */
enum bpf_attach_type expected_attach_type; /* 12 4 */
u32 len; /* 16 4 */
u32 jited_len; /* 20 4 */
union {
u8 digest[32]; /* 24 32 */
u8 tag[8]; /* 24 8 */
}; /* 24 32 */
struct bpf_prog_stats * stats; /* 56 8 */
/* --- cacheline 1 boundary (64 bytes) --- */
u8 * active; /* 64 8 */
unsigned int (*bpf_func)(const void *, const struct
bpf_insn *); /* 72 8 */
struct bpf_prog_aux * aux; /* 80 8 */
struct sock_fprog_kern * orig_prog; /* 88 8 */
union {
struct {
struct {
} __empty_insns; /* 96 0 */
struct sock_filter insns[0]; /* 96 0 */
}; /* 96 0 */
struct {
struct {
} __empty_insnsi; /* 96 0 */
struct bpf_insn insnsi[0]; /* 96 0 */
}; /* 96 0 */
}; /* 96 0 */
/* size: 96, cachelines: 2, members: 29 */
/* sum members: 90 */
/* sum bitfield members: 17 bits, bit holes: 1, sum bit holes: 31 bits */
/* last cacheline: 32 bytes */
};
Luckily, the total size keeps 96 bytes. The layout change is the hole:
from 4 bytes to 31 bits.
Thanks,
Leon
> gpl_compatible:1, /* Is filter GPL compatible? */
> cb_access:1, /* Is control block accessed? */
> dst_needed:1, /* Do we need dst entry? */
> [...]
next prev parent reply other threads:[~2026-07-02 3:17 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-02 2:21 [PATCH bpf-next v5] bpf: Reject programs with inlined helpers if JIT is unavailable Tiezhu Yang
2026-07-02 3:17 ` Leon Hwang [this message]
2026-07-02 3:31 ` Tiezhu Yang
2026-07-02 5:39 ` Alexei Starovoitov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=3fe115fd-8df8-4bf0-805b-2d0c2c40fdf5@linux.dev \
--to=leon.hwang@linux.dev \
--cc=andrii@kernel.org \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=eddyz87@gmail.com \
--cc=emil@etsalapatis.com \
--cc=jolsa@kernel.org \
--cc=kafai.wan@linux.dev \
--cc=loongarch@lists.linux.dev \
--cc=martin.lau@linux.dev \
--cc=memxor@gmail.com \
--cc=song@kernel.org \
--cc=yangtiezhu@loongson.cn \
--cc=yonghong.song@linux.dev \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.