linux-kernel - Re: [PATCH v1 1/3] kallsyms: avoid hardcoding the buffer size

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Date:   Fri, 6 May 2022 14:58:24 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     James Bottomley <James.Bottomley@...senpartnership.com>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Changbin Du <changbin.du@...el.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        rust-for-linux <rust-for-linux@...r.kernel.org>,
        Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH v1 1/3] kallsyms: avoid hardcoding the buffer size

Hi James,

On Fri, May 6, 2022 at 1:19 PM James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
>
> When you raise KSYM_NAME_LEN to 512, this on stack allocation becomes
> 2049 bytes.  How did you manage not to trigger the frame size warning,
> which is 1024 on 32 bit and 2048 on 64 bit by default?

Thanks for taking a look!

If you mean `CONFIG_FRAME_WARN`, that applies to kernel objects, not scripts.

If I enable it for `HOSTCC` with a 2048 threshold, we do get the warning:

    scripts/kallsyms.c: In function 'read_symbol':
    scripts/kallsyms.c:257:1: warning: the frame size of 2080 bytes is
larger than 2048 bytes [-Wframe-larger-than=]
     257 | }
          | ^

as well as in a few other places (e.g. for my config [0]), but given
it is userspace it should be fine unless they happen to end up
recursing quite a few times.

Cheers,
Miguel

[0]
    scripts/mod/modpost.c: In function 'main':
    scripts/mod/modpost.c:2636:1: warning: the frame size of 4208
bytes is larger than 2048 bytes [-Wframe-larger-than=]
     2636 | }
          | ^
    scripts/mod/sumversion.c: In function 'get_src_version':
    scripts/mod/sumversion.c:419:1: warning: the frame size of 4272
bytes is larger than 2048 bytes [-Wframe-larger-than=]
      419 | }
          | ^
    usr/gen_init_cpio.c: In function 'cpio_mkgeneric_line':
    usr/gen_init_cpio.c:223:1: warning: the frame size of 4384 bytes
is larger than 2048 bytes [-Wframe-larger-than=]
      223 | }
          | ^
    usr/gen_init_cpio.c: In function 'cpio_mknod_line':
    usr/gen_init_cpio.c:293:1: warning: the frame size of 4400 bytes
is larger than 2048 bytes [-Wframe-larger-than=]
      293 | }
          | ^
    usr/gen_init_cpio.c: In function 'cpio_mkfile_line':
    usr/gen_init_cpio.c:456:1: warning: the frame size of 12560 bytes
is larger than 2048 bytes [-Wframe-larger-than=]
      456 | }
          | ^
    usr/gen_init_cpio.c: In function 'cpio_mkslink_line':
    usr/gen_init_cpio.c:150:1: warning: the frame size of 8496 bytes
is larger than 2048 bytes [-Wframe-larger-than=]
      150 | }
          | ^
    usr/gen_init_cpio.c: In function 'main':
    usr/gen_init_cpio.c:640:1: warning: the frame size of 8528 bytes
is larger than 2048 bytes [-Wframe-larger-than=]
      640 | }
          | ^
    drivers/tty/vt/conmakehash.c: In function 'main':
    drivers/tty/vt/conmakehash.c:290:1: warning: the frame size of
65584 bytes is larger than 2048 bytes [-Wframe-larger-than=]
      290 | }
          | ^