Re: [PATCH v8 04/13] x86: kexec_file: factor out elf core header related functions

[Dave Young <dyoung@redhat.com>]

Hi AKASHI,
On 02/22/18 at 08:17pm, AKASHI Takahiro wrote:
> exclude_mem_range() and prepare_elf64_headers() can be re-used on other
> architectures, including arm64, as well. So let them factored out so as to
> move them to generic side in the next patch.
> 
> fill_up_crash_elf_data() can potentially be commonalized for most
> architectures who want to go through io resources (/proc/iomem) for a list
> of "System RAM", but leave it private for now.

Is it possible to spilt this patch to small patches?  For example it can
be one patch to change the max ranges to a dynamically allocated buffer.

The remain parts could be splitted as well, so that they can be easier
to review.

> 
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> Cc: Dave Young <dyoung@redhat.com>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Cc: Baoquan He <bhe@redhat.com>
> ---
>  arch/x86/kernel/crash.c | 235 +++++++++++++++++++++---------------------------
>  1 file changed, 103 insertions(+), 132 deletions(-)
> 
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 10e74d4778a1..5c19cfbf3b85 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -41,32 +41,14 @@
>  /* Alignment required for elf header segment */
>  #define ELF_CORE_HEADER_ALIGN   4096
>  
> -/* This primarily represents number of split ranges due to exclusion */
> -#define CRASH_MAX_RANGES	16
> -
>  struct crash_mem_range {
>  	u64 start, end;
>  };
>  
>  struct crash_mem {
> -	unsigned int nr_ranges;
> -	struct crash_mem_range ranges[CRASH_MAX_RANGES];
> -};
> -
> -/* Misc data about ram ranges needed to prepare elf headers */
> -struct crash_elf_data {
> -	struct kimage *image;
> -	/*
> -	 * Total number of ram ranges we have after various adjustments for
> -	 * crash reserved region, etc.
> -	 */
>  	unsigned int max_nr_ranges;
> -
> -	/* Pointer to elf header */
> -	void *ehdr;
> -	/* Pointer to next phdr */
> -	void *bufp;
> -	struct crash_mem mem;
> +	unsigned int nr_ranges;
> +	struct crash_mem_range ranges[0];
>  };
>  
>  /* Used while preparing memory map entries for second kernel */
> @@ -217,29 +199,32 @@ static int get_nr_ram_ranges_callback(struct resource *res, void *arg)
>  	return 0;
>  }
>  
> -
>  /* Gather all the required information to prepare elf headers for ram regions */
> -static void fill_up_crash_elf_data(struct crash_elf_data *ced,
> -				   struct kimage *image)
> +static struct crash_mem *fill_up_crash_elf_data(void)
>  {
>  	unsigned int nr_ranges = 0;
> -
> -	ced->image = image;
> +	struct crash_mem *cmem;
>  
>  	walk_system_ram_res(0, -1, &nr_ranges,
>  				get_nr_ram_ranges_callback);
>  
> -	ced->max_nr_ranges = nr_ranges;
> +	/*
> +	 * Exclusion of crash region and/or crashk_low_res may cause
> +	 * another range split. So add extra two slots here.
> +	 */
> +	nr_ranges += 2;
> +	cmem = vmalloc(sizeof(struct crash_mem) +
> +			sizeof(struct crash_mem_range) * nr_ranges);
> +	if (!cmem)
> +		return NULL;
>  
> -	/* Exclusion of crash region could split memory ranges */
> -	ced->max_nr_ranges++;
> +	cmem->max_nr_ranges = nr_ranges;
> +	cmem->nr_ranges = 0;
>  
> -	/* If crashk_low_res is not 0, another range split possible */
> -	if (crashk_low_res.end)
> -		ced->max_nr_ranges++;
> +	return cmem;
>  }
>  
> -static int exclude_mem_range(struct crash_mem *mem,
> +static int crash_exclude_mem_range(struct crash_mem *mem,
>  		unsigned long long mstart, unsigned long long mend)
>  {
>  	int i, j;
> @@ -293,10 +278,8 @@ static int exclude_mem_range(struct crash_mem *mem,
>  		return 0;
>  
>  	/* Split happened */
> -	if (i == CRASH_MAX_RANGES - 1) {
> -		pr_err("Too many crash ranges after split\n");
> +	if (i == mem->max_nr_ranges - 1)
>  		return -ENOMEM;
> -	}
>  
>  	/* Location where new range should go */
>  	j = i + 1;
> @@ -314,27 +297,20 @@ static int exclude_mem_range(struct crash_mem *mem,
>  
>  /*
>   * Look for any unwanted ranges between mstart, mend and remove them. This
> - * might lead to split and split ranges are put in ced->mem.ranges[] array
> + * might lead to split and split ranges are put in cmem->ranges[] array
>   */
> -static int elf_header_exclude_ranges(struct crash_elf_data *ced,
> -		unsigned long long mstart, unsigned long long mend)
> +static int elf_header_exclude_ranges(struct crash_mem *cmem)
>  {
> -	struct crash_mem *cmem = &ced->mem;
>  	int ret = 0;
>  
> -	memset(cmem->ranges, 0, sizeof(cmem->ranges));
> -
> -	cmem->ranges[0].start = mstart;
> -	cmem->ranges[0].end = mend;
> -	cmem->nr_ranges = 1;
> -
>  	/* Exclude crashkernel region */
> -	ret = exclude_mem_range(cmem, crashk_res.start, crashk_res.end);
> +	ret = crash_exclude_mem_range(cmem, crashk_res.start, crashk_res.end);
>  	if (ret)
>  		return ret;
>  
>  	if (crashk_low_res.end) {
> -		ret = exclude_mem_range(cmem, crashk_low_res.start, crashk_low_res.end);
> +		ret = crash_exclude_mem_range(cmem, crashk_low_res.start,
> +							crashk_low_res.end);
>  		if (ret)
>  			return ret;
>  	}
> @@ -344,70 +320,29 @@ static int elf_header_exclude_ranges(struct crash_elf_data *ced,
>  
>  static int prepare_elf64_ram_headers_callback(struct resource *res, void *arg)
>  {
> -	struct crash_elf_data *ced = arg;
> -	Elf64_Ehdr *ehdr;
> -	Elf64_Phdr *phdr;
> -	unsigned long mstart, mend;
> -	struct kimage *image = ced->image;
> -	struct crash_mem *cmem;
> -	int ret, i;
> +	struct crash_mem *cmem = arg;
>  
> -	ehdr = ced->ehdr;
> -
> -	/* Exclude unwanted mem ranges */
> -	ret = elf_header_exclude_ranges(ced, res->start, res->end);
> -	if (ret)
> -		return ret;
> -
> -	/* Go through all the ranges in ced->mem.ranges[] and prepare phdr */
> -	cmem = &ced->mem;
> -
> -	for (i = 0; i < cmem->nr_ranges; i++) {
> -		mstart = cmem->ranges[i].start;
> -		mend = cmem->ranges[i].end;
> -
> -		phdr = ced->bufp;
> -		ced->bufp += sizeof(Elf64_Phdr);
> -
> -		phdr->p_type = PT_LOAD;
> -		phdr->p_flags = PF_R|PF_W|PF_X;
> -		phdr->p_offset  = mstart;
> -
> -		/*
> -		 * If a range matches backup region, adjust offset to backup
> -		 * segment.
> -		 */
> -		if (mstart == image->arch.backup_src_start &&
> -		    (mend - mstart + 1) == image->arch.backup_src_sz)
> -			phdr->p_offset = image->arch.backup_load_addr;
> -
> -		phdr->p_paddr = mstart;
> -		phdr->p_vaddr = (unsigned long long) __va(mstart);
> -		phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
> -		phdr->p_align = 0;
> -		ehdr->e_phnum++;
> -		pr_debug("Crash PT_LOAD elf header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
> -			phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
> -			ehdr->e_phnum, phdr->p_offset);
> -	}
> +	cmem->ranges[cmem->nr_ranges].start = res->start;
> +	cmem->ranges[cmem->nr_ranges].end = res->end;
> +	cmem->nr_ranges++;
>  
> -	return ret;
> +	return 0;
>  }
>  
> -static int prepare_elf64_headers(struct crash_elf_data *ced,
> -		void **addr, unsigned long *sz)
> +static int crash_prepare_elf64_headers(struct crash_mem *cmem, int kernel_map,
> +					void **addr, unsigned long *sz)
>  {
>  	Elf64_Ehdr *ehdr;
>  	Elf64_Phdr *phdr;
>  	unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
> -	unsigned char *buf, *bufp;
> -	unsigned int cpu;
> +	unsigned char *buf;
> +	unsigned int cpu, i;
>  	unsigned long long notes_addr;
> -	int ret;
> +	unsigned long mstart, mend;
>  
>  	/* extra phdr for vmcoreinfo elf note */
>  	nr_phdr = nr_cpus + 1;
> -	nr_phdr += ced->max_nr_ranges;
> +	nr_phdr += cmem->nr_ranges;
>  
>  	/*
>  	 * kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
> @@ -425,9 +360,8 @@ static int prepare_elf64_headers(struct crash_elf_data *ced,
>  	if (!buf)
>  		return -ENOMEM;
>  
> -	bufp = buf;
> -	ehdr = (Elf64_Ehdr *)bufp;
> -	bufp += sizeof(Elf64_Ehdr);
> +	ehdr = (Elf64_Ehdr *)buf;
> +	phdr = (Elf64_Phdr *)(ehdr + 1);
>  	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
>  	ehdr->e_ident[EI_CLASS] = ELFCLASS64;
>  	ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
> @@ -443,42 +377,51 @@ static int prepare_elf64_headers(struct crash_elf_data *ced,
>  
>  	/* Prepare one phdr of type PT_NOTE for each present cpu */
>  	for_each_present_cpu(cpu) {
> -		phdr = (Elf64_Phdr *)bufp;
> -		bufp += sizeof(Elf64_Phdr);
>  		phdr->p_type = PT_NOTE;
>  		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
>  		phdr->p_offset = phdr->p_paddr = notes_addr;
>  		phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
>  		(ehdr->e_phnum)++;
> +		phdr++;
>  	}
>  
>  	/* Prepare one PT_NOTE header for vmcoreinfo */
> -	phdr = (Elf64_Phdr *)bufp;
> -	bufp += sizeof(Elf64_Phdr);
>  	phdr->p_type = PT_NOTE;
>  	phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
>  	phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
>  	(ehdr->e_phnum)++;
> +	phdr++;
>  
> -#ifdef CONFIG_X86_64
>  	/* Prepare PT_LOAD type program header for kernel text region */
> -	phdr = (Elf64_Phdr *)bufp;
> -	bufp += sizeof(Elf64_Phdr);
> -	phdr->p_type = PT_LOAD;
> -	phdr->p_flags = PF_R|PF_W|PF_X;
> -	phdr->p_vaddr = (Elf64_Addr)_text;
> -	phdr->p_filesz = phdr->p_memsz = _end - _text;
> -	phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
> -	(ehdr->e_phnum)++;
> -#endif
> +	if (kernel_map) {
> +		phdr->p_type = PT_LOAD;
> +		phdr->p_flags = PF_R|PF_W|PF_X;
> +		phdr->p_vaddr = (Elf64_Addr)_text;
> +		phdr->p_filesz = phdr->p_memsz = _end - _text;
> +		phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
> +		ehdr->e_phnum++;
> +		phdr++;
> +	}
>  
> -	/* Prepare PT_LOAD headers for system ram chunks. */
> -	ced->ehdr = ehdr;
> -	ced->bufp = bufp;
> -	ret = walk_system_ram_res(0, -1, ced,
> -			prepare_elf64_ram_headers_callback);
> -	if (ret < 0)
> -		return ret;
> +	/* Go through all the ranges in cmem->ranges[] and prepare phdr */
> +	for (i = 0; i < cmem->nr_ranges; i++) {
> +		mstart = cmem->ranges[i].start;
> +		mend = cmem->ranges[i].end;
> +
> +		phdr->p_type = PT_LOAD;
> +		phdr->p_flags = PF_R|PF_W|PF_X;
> +		phdr->p_offset  = mstart;
> +
> +		phdr->p_paddr = mstart;
> +		phdr->p_vaddr = (unsigned long long) __va(mstart);
> +		phdr->p_filesz = phdr->p_memsz = mend - mstart + 1;
> +		phdr->p_align = 0;
> +		ehdr->e_phnum++;
> +		phdr++;
> +		pr_debug("Crash PT_LOAD elf header. phdr=%p vaddr=0x%llx, paddr=0x%llx, sz=0x%llx e_phnum=%d p_offset=0x%llx\n",
> +			phdr, phdr->p_vaddr, phdr->p_paddr, phdr->p_filesz,
> +			ehdr->e_phnum, phdr->p_offset);
> +	}
>  
>  	*addr = buf;
>  	*sz = elf_sz;
> @@ -489,18 +432,46 @@ static int prepare_elf64_headers(struct crash_elf_data *ced,
>  static int prepare_elf_headers(struct kimage *image, void **addr,
>  					unsigned long *sz)
>  {
> -	struct crash_elf_data *ced;
> -	int ret;
> +	struct crash_mem *cmem;
> +	Elf64_Ehdr *ehdr;
> +	Elf64_Phdr *phdr;
> +	int ret, i;
>  
> -	ced = kzalloc(sizeof(*ced), GFP_KERNEL);
> -	if (!ced)
> +	cmem = fill_up_crash_elf_data();
> +	if (!cmem)
>  		return -ENOMEM;
>  
> -	fill_up_crash_elf_data(ced, image);
> +	ret = walk_system_ram_res(0, -1, cmem,
> +				prepare_elf64_ram_headers_callback);
> +	if (ret)
> +		goto out;
> +
> +	/* Exclude unwanted mem ranges */
> +	ret = elf_header_exclude_ranges(cmem);
> +	if (ret)
> +		goto out;
>  
>  	/* By default prepare 64bit headers */
> -	ret =  prepare_elf64_headers(ced, addr, sz);
> -	kfree(ced);
> +	ret =  crash_prepare_elf64_headers(cmem,
> +				(int)IS_ENABLED(CONFIG_X86_64), addr, sz);
> +	if (ret)
> +		goto out;
> +
> +	/*
> +	 * If a range matches backup region, adjust offset to backup
> +	 * segment.
> +	 */
> +	ehdr = (Elf64_Ehdr *)*addr;
> +	phdr = (Elf64_Phdr *)(ehdr + 1);
> +	for (i = 0; i < ehdr->e_phnum; phdr++, i++)
> +		if (phdr->p_type == PT_LOAD &&
> +				phdr->p_paddr == image->arch.backup_src_start &&
> +				phdr->p_memsz == image->arch.backup_src_sz) {
> +			phdr->p_offset = image->arch.backup_load_addr;
> +			break;
> +		}
> +out:
> +	vfree(cmem);
>  	return ret;
>  }
>  
> @@ -546,14 +517,14 @@ static int memmap_exclude_ranges(struct kimage *image, struct crash_mem *cmem,
>  	/* Exclude Backup region */
>  	start = image->arch.backup_load_addr;
>  	end = start + image->arch.backup_src_sz - 1;
> -	ret = exclude_mem_range(cmem, start, end);
> +	ret = crash_exclude_mem_range(cmem, start, end);
>  	if (ret)
>  		return ret;
>  
>  	/* Exclude elf header region */
>  	start = image->arch.elf_load_addr;
>  	end = start + image->arch.elf_headers_sz - 1;
> -	return exclude_mem_range(cmem, start, end);
> +	return crash_exclude_mem_range(cmem, start, end);
>  }
>  
>  /* Prepare memory map for crash dump kernel */
> -- 
> 2.16.2
> 

Thanks
Dave