Re: [PATCH v6 1/5] vmcore: Introduce ELF header in new memory feature

[Vivek Goyal]

On Mon, Jul 01, 2013 at 09:32:35PM +0200, Michael Holzheu wrote:
> Currently for s390 we create the ELF core header in the 2nd kernel
> with a small trick. We relocate the addresses in the ELF header in
> a way that for the /proc/vmcore code it seems to be in the 1st kernel
> (old) memory and the read_from_oldmem() returns the correct data.
> This allows the /proc/vmcore code to use the ELF header in the
> 2nd kernel.
> 
> This patch now exchanges the old mechanism with the new and much
> cleaner function call override feature that now offcially allows to
> create the ELF core header in the 2nd kernel.
> 
> To use the new feature the following function have to be defined
> by the architecture backend code to read from new memory:
> 
>  * elfcorehdr_alloc: Allocate ELF header
>  * elfcorehdr_free: Free the memory of the ELF header
>  * elfcorehdr_read: Read from ELF header
>  * elfcorehdr_read_notes: Read from ELF notes
> 
> Signed-off-by: Michael Holzheu <holzheu@xxxxxxxxxxxxxxxxxx>

Looks good to me.

Acked-by: Vivek Goyal <vgoyal@xxxxxxxxxx>

Vivek

> ---
>  fs/proc/vmcore.c           | 61 ++++++++++++++++++++++++++++++++++++++--------
>  include/linux/crash_dump.h |  6 +++++
>  2 files changed, 57 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
> index 0f6db52..c28189c 100644
> --- a/fs/proc/vmcore.c
> +++ b/fs/proc/vmcore.c
> @@ -123,6 +123,36 @@ static ssize_t read_from_oldmem(char *buf, size_t count,
>  	return read;
>  }
>  
> +/*
> + * Architectures may override this function to allocate ELF header in 2nd kernel
> + */
> +int __weak elfcorehdr_alloc(unsigned long long *addr, unsigned long long *size)
> +{
> +	return 0;
> +}
> +
> +/*
> + * Architectures may override this function to free header
> + */
> +void __weak elfcorehdr_free(unsigned long long addr)
> +{}
> +
> +/*
> + * Architectures may override this function to read from ELF header
> + */
> +ssize_t __weak elfcorehdr_read(char *buf, size_t count, u64 *ppos)
> +{
> +	return read_from_oldmem(buf, count, ppos, 0);
> +}
> +
> +/*
> + * Architectures may override this function to read from notes sections
> + */
> +ssize_t __weak elfcorehdr_read_notes(char *buf, size_t count, u64 *ppos)
> +{
> +	return read_from_oldmem(buf, count, ppos, 0);
> +}
> +
>  /* Read from the ELF header and then the crash dump. On error, negative value is
>   * returned otherwise number of bytes read are returned.
>   */
> @@ -322,7 +352,7 @@ static int __init update_note_header_size_elf64(const Elf64_Ehdr *ehdr_ptr)
>  		notes_section = kmalloc(max_sz, GFP_KERNEL);
>  		if (!notes_section)
>  			return -ENOMEM;
> -		rc = read_from_oldmem(notes_section, max_sz, &offset, 0);
> +		rc = elfcorehdr_read_notes(notes_section, max_sz, &offset);
>  		if (rc < 0) {
>  			kfree(notes_section);
>  			return rc;
> @@ -409,7 +439,8 @@ static int __init copy_notes_elf64(const Elf64_Ehdr *ehdr_ptr, char *notes_buf)
>  		if (phdr_ptr->p_type != PT_NOTE)
>  			continue;
>  		offset = phdr_ptr->p_offset;
> -		rc = read_from_oldmem(notes_buf, phdr_ptr->p_memsz, &offset, 0);
> +		rc = elfcorehdr_read_notes(notes_buf, phdr_ptr->p_memsz,
> +					   &offset);
>  		if (rc < 0)
>  			return rc;
>  		notes_buf += phdr_ptr->p_memsz;
> @@ -510,7 +541,7 @@ static int __init update_note_header_size_elf32(const Elf32_Ehdr *ehdr_ptr)
>  		notes_section = kmalloc(max_sz, GFP_KERNEL);
>  		if (!notes_section)
>  			return -ENOMEM;
> -		rc = read_from_oldmem(notes_section, max_sz, &offset, 0);
> +		rc = elfcorehdr_read_notes(notes_section, max_sz, &offset);
>  		if (rc < 0) {
>  			kfree(notes_section);
>  			return rc;
> @@ -597,7 +628,8 @@ static int __init copy_notes_elf32(const Elf32_Ehdr *ehdr_ptr, char *notes_buf)
>  		if (phdr_ptr->p_type != PT_NOTE)
>  			continue;
>  		offset = phdr_ptr->p_offset;
> -		rc = read_from_oldmem(notes_buf, phdr_ptr->p_memsz, &offset, 0);
> +		rc = elfcorehdr_read_notes(notes_buf, phdr_ptr->p_memsz,
> +					   &offset);
>  		if (rc < 0)
>  			return rc;
>  		notes_buf += phdr_ptr->p_memsz;
> @@ -793,7 +825,7 @@ static int __init parse_crash_elf64_headers(void)
>  	addr = elfcorehdr_addr;
>  
>  	/* Read Elf header */
> -	rc = read_from_oldmem((char*)&ehdr, sizeof(Elf64_Ehdr), &addr, 0);
> +	rc = elfcorehdr_read((char *)&ehdr, sizeof(Elf64_Ehdr), &addr);
>  	if (rc < 0)
>  		return rc;
>  
> @@ -820,7 +852,7 @@ static int __init parse_crash_elf64_headers(void)
>  	if (!elfcorebuf)
>  		return -ENOMEM;
>  	addr = elfcorehdr_addr;
> -	rc = read_from_oldmem(elfcorebuf, elfcorebuf_sz_orig, &addr, 0);
> +	rc = elfcorehdr_read(elfcorebuf, elfcorebuf_sz_orig, &addr);
>  	if (rc < 0)
>  		goto fail;
>  
> @@ -849,7 +881,7 @@ static int __init parse_crash_elf32_headers(void)
>  	addr = elfcorehdr_addr;
>  
>  	/* Read Elf header */
> -	rc = read_from_oldmem((char*)&ehdr, sizeof(Elf32_Ehdr), &addr, 0);
> +	rc = elfcorehdr_read((char *)&ehdr, sizeof(Elf32_Ehdr), &addr);
>  	if (rc < 0)
>  		return rc;
>  
> @@ -875,7 +907,7 @@ static int __init parse_crash_elf32_headers(void)
>  	if (!elfcorebuf)
>  		return -ENOMEM;
>  	addr = elfcorehdr_addr;
> -	rc = read_from_oldmem(elfcorebuf, elfcorebuf_sz_orig, &addr, 0);
> +	rc = elfcorehdr_read(elfcorebuf, elfcorebuf_sz_orig, &addr);
>  	if (rc < 0)
>  		goto fail;
>  
> @@ -902,7 +934,7 @@ static int __init parse_crash_elf_headers(void)
>  	int rc=0;
>  
>  	addr = elfcorehdr_addr;
> -	rc = read_from_oldmem(e_ident, EI_NIDENT, &addr, 0);
> +	rc = elfcorehdr_read(e_ident, EI_NIDENT, &addr);
>  	if (rc < 0)
>  		return rc;
>  	if (memcmp(e_ident, ELFMAG, SELFMAG) != 0) {
> @@ -935,7 +967,14 @@ static int __init vmcore_init(void)
>  {
>  	int rc = 0;
>  
> -	/* If elfcorehdr= has been passed in cmdline, then capture the dump.*/
> +	/* Allow architectures to allocate ELF header in 2nd kernel */
> +	rc = elfcorehdr_alloc(&elfcorehdr_addr, &elfcorehdr_size);
> +	if (rc)
> +		return rc;
> +	/*
> +	 * If elfcorehdr= has been passed in cmdline or created in 2nd kernel,
> +	 * then capture the dump.
> +	 */
>  	if (!(is_vmcore_usable()))
>  		return rc;
>  	rc = parse_crash_elf_headers();
> @@ -943,6 +982,8 @@ static int __init vmcore_init(void)
>  		pr_warn("Kdump: vmcore not initialized\n");
>  		return rc;
>  	}
> +	elfcorehdr_free(elfcorehdr_addr);
> +	elfcorehdr_addr = ELFCORE_ADDR_ERR;
>  
>  	proc_vmcore = proc_create("vmcore", S_IRUSR, NULL, &proc_vmcore_operations);
>  	if (proc_vmcore)
> diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
> index 37e4f8d..6571f82 100644
> --- a/include/linux/crash_dump.h
> +++ b/include/linux/crash_dump.h
> @@ -12,6 +12,12 @@
>  extern unsigned long long elfcorehdr_addr;
>  extern unsigned long long elfcorehdr_size;
>  
> +extern int __weak elfcorehdr_alloc(unsigned long long *addr,
> +				   unsigned long long *size);
> +extern void __weak elfcorehdr_free(unsigned long long addr);
> +extern ssize_t __weak elfcorehdr_read(char *buf, size_t count, u64 *ppos);
> +extern ssize_t __weak elfcorehdr_read_notes(char *buf, size_t count, u64 *ppos);
> +
>  extern ssize_t copy_oldmem_page(unsigned long, char *, size_t,
>  						unsigned long, int);
>  
> -- 
> 1.8.2.2
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