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[23.128.96.18]) by mx.google.com with ESMTP id f9si11309521edx.175.2020.06.16.10.24.58; Tue, 16 Jun 2020 10:25:21 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@linux.microsoft.com header.s=default header.b=CuUemv0O; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linux.microsoft.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730222AbgFPRWl (ORCPT + 99 others); Tue, 16 Jun 2020 13:22:41 -0400 Received: from linux.microsoft.com ([13.77.154.182]:59212 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726573AbgFPRWj (ORCPT ); Tue, 16 Jun 2020 13:22:39 -0400 Received: from sequoia (162-237-133-238.lightspeed.rcsntx.sbcglobal.net [162.237.133.238]) by linux.microsoft.com (Postfix) with ESMTPSA id 8467D20B4780; Tue, 16 Jun 2020 10:22:37 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 8467D20B4780 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1592328158; bh=Va/z/RCQjkwx4GMOEW6jvTREyv5bVvF1H/LITP0NJyY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=CuUemv0O4XfTcx4Gin5xK0vy6ekfHBp24Jy+GB7UYJQC9elKaJqqNan6+VNY/q1NE StNnnOB5KYPqzXz82m7khMJT37SaDN/CqxSGDaPj17YVDd7VqiAJQtZaBU/x5CJeJh 3YaonZT4/Ji1jJ+X4vtyjbY6It+aM6NiLc4EMNQU= Date: Tue, 16 Jun 2020 12:22:35 -0500 From: Tyler Hicks To: Vijay Balakrishna Cc: Dave Young , Baoquan He , Vivek Goyal , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com Subject: Re: [PATCH v2][RFC] kdump: append kernel build-id string to VMCOREINFO Message-ID: <20200616172235.GB1409697@sequoia> References: <1591849672-34104-1-git-send-email-vijayb@linux.microsoft.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1591849672-34104-1-git-send-email-vijayb@linux.microsoft.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-06-10 21:27:52, Vijay Balakrishna wrote: > Make kernel GNU build-id available in VMCOREINFO. Having > build-id in VMCOREINFO facilitates presenting appropriate kernel > namelist image with debug information file to kernel crash dump > analysis tools. Currently VMCOREINFO lacks uniquely identifiable > key for crash analysis automation. > > Regarding if this patch is necessary or matching of linux_banner > and OSRELEASE in VMCOREINFO employed by crash(8) meets the > need -- IMO, build-id approach more foolproof, in most instances it > is a cryptographic hash generated using internal code/ELF bits unlike > kernel version string upon which linux_banner is based that is > external to the code. I feel each is intended for a different purpose. > Also OSRELEASE is not suitable when two different kernel builds > from same version with different features enabled. > > Currently for most linux (and non-linux) systems build-id can be > extracted using standard methods for file types such as user mode crash > dumps, shared libraries, loadable kernel modules etc., This is an > exception for linux kernel dump. Having build-id in VMCOREINFO brings > some uniformity for automation tools. > > Signed-off-by: Vijay Balakrishna I think this is a nice improvement over today's linux_banner approach for correlating vmlinux to a kernel dump. The elf notes parsing in this patch lines up with what is described in in the "Notes (Nhdr)" section of the elf(5) man page. BUILD_ID_MAX is sufficient to hold a sha1 build-id, which is the default build-id type today in GNU ld(2). It is also sufficient to hold the "fast" build-id, which is the default build-id type today in LLVM lld(2). Therefore, Reviewed-by: Tyler Hicks Thanks! Tyler > --- > Changes since v2: > ----------------- > - v1 was sent out as a single patch which can be seen here: > http://lists.infradead.org/pipermail/kexec/2020-June/025202.html > - moved justification to commit commit log > - renamed 'g_build_id' to 'note_sec' > - fixed format specifier in pr_warn() from '%lu' to '%u' (failed to > catch warning in v1) > > include/linux/crash_core.h | 6 +++++ > kernel/crash_core.c | 50 ++++++++++++++++++++++++++++++++++++++ > 2 files changed, 56 insertions(+) > > diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h > index 525510a9f965..6594dbc34a37 100644 > --- a/include/linux/crash_core.h > +++ b/include/linux/crash_core.h > @@ -38,6 +38,8 @@ phys_addr_t paddr_vmcoreinfo_note(void); > > #define VMCOREINFO_OSRELEASE(value) \ > vmcoreinfo_append_str("OSRELEASE=%s\n", value) > +#define VMCOREINFO_BUILD_ID(value) \ > + vmcoreinfo_append_str("BUILD-ID=%s\n", value) > #define VMCOREINFO_PAGESIZE(value) \ > vmcoreinfo_append_str("PAGESIZE=%ld\n", value) > #define VMCOREINFO_SYMBOL(name) \ > @@ -64,6 +66,10 @@ extern unsigned char *vmcoreinfo_data; > extern size_t vmcoreinfo_size; > extern u32 *vmcoreinfo_note; > > +/* raw contents of kernel .notes section */ > +extern const void __start_notes __weak; > +extern const void __stop_notes __weak; > + > Elf_Word *append_elf_note(Elf_Word *buf, char *name, unsigned int type, > void *data, size_t data_len); > void final_note(Elf_Word *buf); > diff --git a/kernel/crash_core.c b/kernel/crash_core.c > index 9f1557b98468..64ac359cd17e 100644 > --- a/kernel/crash_core.c > +++ b/kernel/crash_core.c > @@ -11,6 +11,8 @@ > #include > #include > > +#include > + > /* vmcoreinfo stuff */ > unsigned char *vmcoreinfo_data; > size_t vmcoreinfo_size; > @@ -376,6 +378,53 @@ phys_addr_t __weak paddr_vmcoreinfo_note(void) > } > EXPORT_SYMBOL(paddr_vmcoreinfo_note); > > +#define NOTES_SIZE (&__stop_notes - &__start_notes) > +#define BUILD_ID_MAX SHA1_DIGEST_SIZE > +#define NT_GNU_BUILD_ID 3 > + > +struct elf_note_section { > + struct elf_note n_hdr; > + u8 n_data[]; > +}; > + > +/* > + * Add build ID from .notes section as generated by the GNU ld(1) > + * or LLVM lld(1) --build-id option. > + */ > +static void add_build_id_vmcoreinfo(void) > +{ > + char build_id[BUILD_ID_MAX * 2 + 1]; > + int n_remain = NOTES_SIZE; > + > + while (n_remain >= sizeof(struct elf_note)) { > + const struct elf_note_section *note_sec = > + &__start_notes + NOTES_SIZE - n_remain; > + const u32 n_namesz = note_sec->n_hdr.n_namesz; > + > + if (note_sec->n_hdr.n_type == NT_GNU_BUILD_ID && > + n_namesz != 0 && > + !strcmp((char *)¬e_sec->n_data[0], "GNU")) { > + if (note_sec->n_hdr.n_descsz <= BUILD_ID_MAX) { > + const u32 n_descsz = note_sec->n_hdr.n_descsz; > + const u8 *s = ¬e_sec->n_data[n_namesz]; > + > + s = PTR_ALIGN(s, 4); > + bin2hex(build_id, s, n_descsz); > + build_id[2 * n_descsz] = '\0'; > + VMCOREINFO_BUILD_ID(build_id); > + return; > + } > + pr_warn("Build ID is too large to include in vmcoreinfo: %u > %u\n", > + note_sec->n_hdr.n_descsz, > + BUILD_ID_MAX); > + return; > + } > + n_remain -= sizeof(struct elf_note) + > + ALIGN(note_sec->n_hdr.n_namesz, 4) + > + ALIGN(note_sec->n_hdr.n_descsz, 4); > + } > +} > + > static int __init crash_save_vmcoreinfo_init(void) > { > vmcoreinfo_data = (unsigned char *)get_zeroed_page(GFP_KERNEL); > @@ -394,6 +443,7 @@ static int __init crash_save_vmcoreinfo_init(void) > } > > VMCOREINFO_OSRELEASE(init_uts_ns.name.release); > + add_build_id_vmcoreinfo(); > VMCOREINFO_PAGESIZE(PAGE_SIZE); > > VMCOREINFO_SYMBOL(init_uts_ns); > -- > 2.26.2