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Date:   Tue, 2 Mar 2021 16:19:09 +0800
From:   Baoquan He <bhe@redhat.com>
To:     Stephen Boyd <swboyd@chromium.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Jessica Yu <jeyu@kernel.org>, kexec@lists.infradead.org,
        linux-kernel@vger.kernel.org, Evan Green <evgreen@chromium.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Jiri Olsa <jolsa@kernel.org>,
        Hsin-Yi Wang <hsinyi@chromium.org>,
        Dave Young <dyoung@redhat.com>, Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [PATCH 7/7] kdump: Use vmlinux_build_id() to simplify
Message-ID: <20210302081909.GA28599@MiWiFi-R3L-srv>
References: <20210301174749.1269154-1-swboyd@chromium.org>
 <20210301174749.1269154-8-swboyd@chromium.org>
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On 03/01/21 at 09:47am, Stephen Boyd wrote:
> We can use the vmlinux_build_id() helper here now instead of open coding
> it. This consolidates code and possibly avoids calculating the build ID
> twice in the case of a crash with a stacktrace.
> 
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Jessica Yu <jeyu@kernel.org>
> Cc: Evan Green <evgreen@chromium.org>
> Cc: Hsin-Yi Wang <hsinyi@chromium.org>
> Cc: Dave Young <dyoung@redhat.com>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Cc: <kexec@lists.infradead.org>
> Signed-off-by: Stephen Boyd <swboyd@chromium.org>
> ---
>  kernel/crash_core.c | 46 ++++++++-------------------------------------
>  1 file changed, 8 insertions(+), 38 deletions(-)
> 
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 825284baaf46..07d3e1109a8c 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -4,6 +4,7 @@
>   * Copyright (C) 2002-2004 Eric Biederman  <ebiederm@xmission.com>
>   */
>  
> +#include <linux/buildid.h>
>  #include <linux/crash_core.h>
>  #include <linux/utsname.h>
>  #include <linux/vmalloc.h>
> @@ -378,51 +379,20 @@ 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 *)&note_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 = &note_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);
> +	const char *build_id = vmlinux_build_id();

It's strange that I can only see the cover letter and this patch 7,
couldn't find the patch where vmlinux_build_id() is introduced in lkml.

> +
> +	if (build_id[0] == '\0') {
> +		pr_warn("Build ID cannot be included in vmcoreinfo\n");
> +		return;
>  	}
> +
> +	VMCOREINFO_BUILD_ID(build_id);
>  }
>  
>  static int __init crash_save_vmcoreinfo_init(void)
> -- 
> https://chromeos.dev
> 
> 
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>