From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7CED374BE4; Mon, 15 Apr 2024 14:55:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713192915; cv=none; b=tppAJLtguHSyO0EwBPKjwpuYIfvYQAYXZtp6wMxHGAWtjuII85tnyglqtQulLXQjoWGl2GPjp7fADTnuYCKfN6dQc+Yz0Gu84LlA3TDR0GBdXOvpFuhfihulLAIuzYXWRl6UTg+CfZqO9Tjuk++mZUEvzmQgqq09UUwJWcorIaM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713192915; c=relaxed/simple; bh=yDn2hW/lNFEjQCB1gxGyWpykAsZ3yzu0fv+O3nmo+PE=; h=MIME-Version:References:In-Reply-To:From:Date:Message-ID:Subject: To:Cc:Content-Type; b=CGWhsuej951CjiHh7zC6u6iDyjoFdVuzXe/JtwgOQzXfWQRaG8bU1rEU+hEuuEGyAvNZEsxX+fPHLFvYUBQXUzx3G/f4lh6ej+rEMfI0xI8TIzofQbcZsXdzBkCU3/itIczTeEDWiuqY/qe3X8xvDpb2m046ItFZNTcdeMrgIt8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YUVBaWHC; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="YUVBaWHC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1A11CC4AF08; Mon, 15 Apr 2024 14:55:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1713192915; bh=yDn2hW/lNFEjQCB1gxGyWpykAsZ3yzu0fv+O3nmo+PE=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=YUVBaWHCqoTZA1fwuUTuWrQYuIaHl07F30+pdiye78ib3MaJle4fCRW+GaQFHeNad s1q5yzrh+OPAw4JOlE1DA6c7nDpPWToQQiu86/CdsqR2WDf4R3+ssA8y+DTg4FgaYO hVm6CwxVJarnq2SQsHFMNayI+ZxDhufQkiJ3nZLq5Hbezx2TfxMFGP7ug0+rrT3asj yp01OLtOx9agxqf8TEgikVU/cB+8v8OseFvSwpzPAiwDR/iv1ljVbEDM6OAljUu5wP lWBu4vERska4tiRfET2dkpBTt2gMym43T97a7/I7PJ1FgrnFp/Xyd/lCjUw6H4XPhk XXGjY2a776kBg== Received: by mail-lj1-f174.google.com with SMTP id 38308e7fff4ca-2d886f17740so48714951fa.1; Mon, 15 Apr 2024 07:55:14 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCUHDJmmqr03FjFGA+Ni0paQTsFsGvm0D6Dtw5l/Z0PdqSiK5RJhJ1yD13kso1y5PteaUKxn/3DmLP/nCgGrLNPL1CLKTADDbi8SFm2j4S8NQMSmVhRvth/osts8Qgkv6+gDqLmKe3YoyHMZG3E3LA2pl5cj/5mQCq7pY45w4w== X-Gm-Message-State: AOJu0YzcvSCUKOwv8pR9mdHmM7vEfLuT4YXcq5adRecSEEs+44PKr83T EFvdvu1PbFbuY3o1MLMBFpx0dr3oZyOidQ60Xe1/58c/0VE7GfV11b1rzpIDuoimFPe3xbUTxPP 4NWrL1jBnzI6mjaz0aszrrq36jyM= X-Google-Smtp-Source: AGHT+IGQ66Ve/NazfhjLkQ0OmB02ih7SC/F0MlgKeiiSMdYkZqeA6tfSUqtsfh0RVGBInJp+sSOUvbycEEPYREWcdYk= X-Received: by 2002:a2e:a418:0:b0:2da:6f6e:ebda with SMTP id p24-20020a2ea418000000b002da6f6eebdamr1153991ljn.24.1713192913761; Mon, 15 Apr 2024 07:55:13 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20240415075837.2349766-5-ardb+git@google.com> <20240415075837.2349766-8-ardb+git@google.com> In-Reply-To: <20240415075837.2349766-8-ardb+git@google.com> From: Masahiro Yamada Date: Mon, 15 Apr 2024 23:54:37 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v3 3/3] btf: Avoid weak external references To: Ard Biesheuvel Cc: linux-kernel@vger.kernel.org, Ard Biesheuvel , Arnd Bergmann , Martin KaFai Lau , linux-arch@vger.kernel.org, linux-kbuild@vger.kernel.org, bpf@vger.kernel.org, Andrii Nakryiko , Jiri Olsa Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, Apr 15, 2024 at 4:58=E2=80=AFPM Ard Biesheuvel wrote: > > From: Ard Biesheuvel > > If the BTF code is enabled in the build configuration, the start/stop > BTF markers are guaranteed to exist in the final link but not during the > first linker pass. > > Avoid GOT based relocations to these markers in the final executable by > providing preliminary definitions that will be used by the first linker > pass, and superseded by the actual definitions in the subsequent ones. > > Make the preliminary definitions dependent on CONFIG_DEBUG_INFO_BTF so > that inadvertent references to this section will trigger a link failure > if they occur in code that does not honour CONFIG_DEBUG_INFO_BTF. > > Note that Clang will notice that taking the address of__start_BTF cannot > yield NULL any longer, so testing for that condition is no longer > needed. > > Acked-by: Andrii Nakryiko > Acked-by: Arnd Bergmann > Signed-off-by: Ard Biesheuvel > --- > include/asm-generic/vmlinux.lds.h | 9 +++++++++ > kernel/bpf/btf.c | 7 +++++-- > kernel/bpf/sysfs_btf.c | 6 +++--- > 3 files changed, 17 insertions(+), 5 deletions(-) > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmli= nux.lds.h > index e8449be62058..4cb3d88449e5 100644 > --- a/include/asm-generic/vmlinux.lds.h > +++ b/include/asm-generic/vmlinux.lds.h > @@ -456,6 +456,7 @@ > * independent code. > */ > #define PRELIMINARY_SYMBOL_DEFINITIONS \ > + PRELIMINARY_BTF_DEFINITIONS \ > PROVIDE(kallsyms_addresses =3D .); = \ > PROVIDE(kallsyms_offsets =3D .); = \ > PROVIDE(kallsyms_names =3D .); = \ > @@ -466,6 +467,14 @@ > PROVIDE(kallsyms_markers =3D .); = \ > PROVIDE(kallsyms_seqs_of_names =3D .); > > +#ifdef CONFIG_DEBUG_INFO_BTF > +#define PRELIMINARY_BTF_DEFINITIONS \ > + PROVIDE(__start_BTF =3D .); = \ > + PROVIDE(__stop_BTF =3D .); > +#else > +#define PRELIMINARY_BTF_DEFINITIONS > +#endif > + Is this necessary? The following code (BOUNDED_SECTION_BY) produces __start_BTF and __stop_BTF symbols under the same condition. /* * .BTF */ #ifdef CONFIG_DEBUG_INFO_BTF #define BTF = \ .BTF : AT(ADDR(.BTF) - LOAD_OFFSET) { = \ BOUNDED_SECTION_BY(.BTF, _BTF) = \ } \ . =3D ALIGN(4); = \ .BTF_ids : AT(ADDR(.BTF_ids) - LOAD_OFFSET) { = \ *(.BTF_ids) = \ } #else #define BTF #endif > /* > * Read only Data > */ > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c > index 90c4a32d89ff..6d46cee47ae3 100644 > --- a/kernel/bpf/btf.c > +++ b/kernel/bpf/btf.c > @@ -5642,8 +5642,8 @@ static struct btf *btf_parse(const union bpf_attr *= attr, bpfptr_t uattr, u32 uat > return ERR_PTR(err); > } > > -extern char __weak __start_BTF[]; > -extern char __weak __stop_BTF[]; > +extern char __start_BTF[]; > +extern char __stop_BTF[]; > extern struct btf *btf_vmlinux; > > #define BPF_MAP_TYPE(_id, _ops) > @@ -5971,6 +5971,9 @@ struct btf *btf_parse_vmlinux(void) > struct btf *btf =3D NULL; > int err; > > + if (!IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) > + return ERR_PTR(-ENOENT); > + > env =3D kzalloc(sizeof(*env), GFP_KERNEL | __GFP_NOWARN); > if (!env) > return ERR_PTR(-ENOMEM); > diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c > index ef6911aee3bb..fedb54c94cdb 100644 > --- a/kernel/bpf/sysfs_btf.c > +++ b/kernel/bpf/sysfs_btf.c > @@ -9,8 +9,8 @@ > #include > > /* See scripts/link-vmlinux.sh, gen_btf() func for details */ > -extern char __weak __start_BTF[]; > -extern char __weak __stop_BTF[]; > +extern char __start_BTF[]; > +extern char __stop_BTF[]; > > static ssize_t > btf_vmlinux_read(struct file *file, struct kobject *kobj, > @@ -32,7 +32,7 @@ static int __init btf_vmlinux_init(void) > { > bin_attr_btf_vmlinux.size =3D __stop_BTF - __start_BTF; > > - if (!__start_BTF || bin_attr_btf_vmlinux.size =3D=3D 0) > + if (bin_attr_btf_vmlinux.size =3D=3D 0) > return 0; > > btf_kobj =3D kobject_create_and_add("btf", kernel_kobj); > -- > 2.44.0.683.g7961c838ac-goog > --=20 Best Regards Masahiro Yamada