[Crash-utility] [PATCH 3/3] arm/arm64: read elf notes for qemu generated cores

[Dave Anderson]

----- Original Message -----
> QEMU can generate both non-makedumpfile (just elf) and makedumpfile
> formatted kdumps. In neither case will crash_notes have prstatus, as
> crash_kexec doesn't run in the kernel, however the elf notes will
> contain the prstatus, and we can dig them out of there.

Hi Andrew,

Refresh my memory -- without the patch, what does "bt" do when run
against the active tasks from QEMU generated dumps?

Dave


> ---
>  arm.c     | 22 ++++++++++++++++++++++
>  arm64.c   | 22 ++++++++++++++++++++++
>  defs.h    |  1 +
>  netdump.c | 21 +++++++++++++++++++++
>  4 files changed, 66 insertions(+)
> 
> diff --git a/arm.c b/arm.c
> index ffc7c06d0f42c..8fc3d48a8ac89 100644
> --- a/arm.c
> +++ b/arm.c
> @@ -597,6 +597,28 @@ arm_get_crash_notes(void)
>  		note = (Elf32_Nhdr *)buf;
>  		p = buf + sizeof(Elf32_Nhdr);
>  
> +		/*
> +		 * dumpfiles created with qemu won't have crash_notes, but there will
> +		 * be elf notes.
> +		 */
> +		if (note->n_namesz == 0 && (DISKDUMP_DUMPFILE() || KDUMP_DUMPFILE())) {
> +			if (DISKDUMP_DUMPFILE())
> +				note = diskdump_get_prstatus_percpu(i);
> +			else if (KDUMP_DUMPFILE())
> +				note = netdump_get_prstatus_percpu(i);
> +			if (note) {
> +				/*
> +				 * SIZE(note_buf) accounts for a "final note", which is a
> +				 * trailing empty elf note header.
> +				 */
> +				long notesz = SIZE(note_buf) - sizeof(Elf32_Nhdr);
> +
> +				if (sizeof(Elf32_Nhdr) + roundup(note->n_namesz, 4) +
> +				    note->n_descsz == notesz)
> +					BCOPY((char *)note, buf, notesz);
> +			}
> +		}
> +
>  		if (note->n_type != NT_PRSTATUS) {
>  			error(WARNING, "invalid note (n_type != NT_PRSTATUS)\n");
>  			goto fail;
> diff --git a/arm64.c b/arm64.c
> index 6187b96d25a4d..91b35787e6942 100644
> --- a/arm64.c
> +++ b/arm64.c
> @@ -1827,6 +1827,28 @@ arm64_get_crash_notes(void)
>  		note = (Elf64_Nhdr *)buf;
>  		p = buf + sizeof(Elf64_Nhdr);
>  
> +		/*
> +		 * dumpfiles created with qemu won't have crash_notes, but there will
> +		 * be elf notes.
> +		 */
> +		if (note->n_namesz == 0 && (DISKDUMP_DUMPFILE() || KDUMP_DUMPFILE())) {
> +			if (DISKDUMP_DUMPFILE())
> +				note = diskdump_get_prstatus_percpu(i);
> +			else if (KDUMP_DUMPFILE())
> +				note = netdump_get_prstatus_percpu(i);
> +			if (note) {
> +				/*
> +				 * SIZE(note_buf) accounts for a "final note", which is a
> +				 * trailing empty elf note header.
> +				 */
> +				long notesz = SIZE(note_buf) - sizeof(Elf64_Nhdr);
> +
> +				if (sizeof(Elf64_Nhdr) + roundup(note->n_namesz, 4) +
> +				    note->n_descsz == notesz)
> +					BCOPY((char *)note, buf, notesz);
> +			}
> +		}
> +
>  		if (note->n_type != NT_PRSTATUS) {
>  			error(WARNING, "invalid note (n_type != NT_PRSTATUS)\n");
>  			goto fail;
> diff --git a/defs.h b/defs.h
> index 1bcd1b3b177db..981b030cc6688 100644
> --- a/defs.h
> +++ b/defs.h
> @@ -5722,6 +5722,7 @@ void dump_registers_for_qemu_mem_dump(void);
>  void kdump_backup_region_init(void);
>  void display_regs_from_elf_notes(int, FILE *);
>  void display_ELF_note(int, int, void *, FILE *);
> +void *netdump_get_prstatus_percpu(int);
>  #define PRSTATUS_NOTE (1)
>  #define QEMU_NOTE     (2)
>  
> diff --git a/netdump.c b/netdump.c
> index bfa818fdef8e1..3ff49f0577c23 100644
> --- a/netdump.c
> +++ b/netdump.c
> @@ -2345,6 +2345,27 @@ dump_Elf64_Nhdr(Elf64_Off offset, int store)
>  	return len;
>  }
>  
> +void *
> +netdump_get_prstatus_percpu(int cpu)
> +{
> +	int online;
> +
> +	if ((cpu < 0) || (cpu >= nd->num_prstatus_notes))
> +		return NULL;
> +
> +	/*
> +	 * If no cpu mapping was done, then there must be
> +	 * a one-to-one relationship between the number
> +	 * of online cpus and the number of notes.
> +	 */
> +	if ((online = get_cpus_online()) &&
> +	    (online == kt->cpus) &&
> +	    (online != nd->num_prstatus_notes))
> +		return NULL;
> +
> +	return nd->nt_prstatus_percpu[cpu];
> +}
> +
>  /*
>   *  Send the request to the proper architecture hander.
>   */
> --
> 2.4.3
> 
>