Re: [PATCH v3 12/12] kdump: Use vmlinux_build_id to simplify

[Baoquan He]

On 04/07/21 at 07:03pm, Petr Mladek wrote:
> On Tue 2021-03-30 20:05:20, Stephen Boyd wrote:
> > We can use the vmlinux_build_id array here now instead of open coding
> > it. This mostly consolidates code.
> > 
> > Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> > Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> > Cc: Jessica Yu <jeyu@xxxxxxxxxx>
> > Cc: Evan Green <evgreen@xxxxxxxxxxxx>
> > Cc: Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx>
> > Cc: Dave Young <dyoung@xxxxxxxxxx>
> > Cc: Baoquan He <bhe@xxxxxxxxxx>
> > Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
> > Cc: <kexec@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
> > ---
> >  include/linux/crash_core.h |  6 +-----
> >  kernel/crash_core.c        | 41 ++------------------------------------
> >  2 files changed, 3 insertions(+), 44 deletions(-)
> > 
> > diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> > index 206bde8308b2..fb8ab99bb2ee 100644
> > --- a/include/linux/crash_core.h
> > +++ b/include/linux/crash_core.h
> > @@ -39,7 +39,7 @@ 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)
> > +	vmcoreinfo_append_str("BUILD-ID=%20phN\n", value)

I may miss something, wondering why we need add '20' here.

> 
> Please, add also build check that BUILD_ID_MAX == 20.
> 
> 
> >  #define VMCOREINFO_PAGESIZE(value) \
> >  	vmcoreinfo_append_str("PAGESIZE=%ld\n", value)
> >  #define VMCOREINFO_SYMBOL(name) \
> > @@ -69,10 +69,6 @@ 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 825284baaf46..6b560cf9f374 100644
> > --- a/kernel/crash_core.c
> > +++ b/kernel/crash_core.c
> > @@ -4,6 +4,7 @@
> >   * Copyright (C) 2002-2004 Eric Biederman  <ebiederm@xxxxxxxxxxxx>
> >   */
> >  
> > +#include <linux/buildid.h>
> >  #include <linux/crash_core.h>
> >  #include <linux/utsname.h>
> >  #include <linux/vmalloc.h>
> > @@ -378,51 +379,13 @@ 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);
> > -	}
> > +	VMCOREINFO_BUILD_ID(vmlinux_build_id);
> >  }
> 
> The function add_build_id_vmcoreinfo() is used in
> crash_save_vmcoreinfo_init() in this context:
> 
> 
> 	VMCOREINFO_OSRELEASE(init_uts_ns.name.release);
> 	add_build_id_vmcoreinfo();
> 	VMCOREINFO_PAGESIZE(PAGE_SIZE);
> 
> 	VMCOREINFO_SYMBOL(init_uts_ns);
> 	VMCOREINFO_OFFSET(uts_namespace, name);
> 	VMCOREINFO_SYMBOL(node_online_map);
> 
> The function is not longer need. VMCOREINFO_BUILD_ID()
> can be used directly:
> 
> 	VMCOREINFO_OSRELEASE(init_uts_ns.name.release);
> 	VMCOREINFO_BUILD_ID(vmlinux_build_id);
> 	VMCOREINFO_PAGESIZE(PAGE_SIZE);
> 
> 	VMCOREINFO_SYMBOL(init_uts_ns);
> 	VMCOREINFO_OFFSET(uts_namespace, name);
> 	VMCOREINFO_SYMBOL(node_online_map);
> 
> 
> Best Regards,
> Petr
> 
> 
> >  
> >  static int __init crash_save_vmcoreinfo_init(void)
> > -- 
> > https://chromeos.dev
>