Re: [PATCH v3] elf: add 64 bits elf loading support

[Oleksij Rempel <o.rempel@pengutronix.de>]

Hi Clement,

thank you for your patch. I tested it on MIPS32 system.

I get this compile warning:
arch/mips/lib/bootm.c: In function 'do_bootm_elf':
arch/mips/lib/bootm.c:75:10: warning: cast to pointer from integer of different size 
[-Wint-to-pointer-cast]
   entry = (void *)elf->entry;
           ^

Kernel boot is working.
Tested-by: Oleksij Rempel <o.rempel@pengutronix.de>

On 01.09.19 16:09, Clement Leger wrote:
> From: Clement Leger <clement.leger@kalray.eu>
> 
> This patch add elf64 loading support to the elf loader. Since
> elf32 and elf64 uses completely different types, to avoid copying all
> the code and simply replace elf32 with elf64, use a macro which will
> return the appropriate field for each type of header. This macro
> generates getter for elf structures according to the class of the loaded
> elf.
> All direct elf struct dereference are then replaced by call to generated
> functions. THis allows to keep a common loader code even if types are
> different.
> 
> Signed-off-by: Clement Leger <cleger@kalray.eu>
> ---
> V3:
> - Compiled on ARM with 32bit toolchain (no warning)
> - Add Signed-off-by.
> 
>   common/elf.c  | 45 +++++++++++++++++++++++----------------------
>   include/elf.h | 29 ++++++++++++++++++++++++++++-
>   2 files changed, 51 insertions(+), 23 deletions(-)
> 
> diff --git a/common/elf.c b/common/elf.c
> index 8edf38856..4733accb0 100644
> --- a/common/elf.c
> +++ b/common/elf.c
> @@ -45,29 +45,31 @@ static void elf_release_regions(struct elf_image *elf)
>   
>   
>   static int load_elf_phdr_segment(struct elf_image *elf, void *src,
> -				 Elf32_Phdr *phdr)
> +				 void *phdr)
>   {
> -	void *dst = (void *)phdr->p_paddr;
> +	void *dst = (void *) elf_phdr_p_paddr(elf, phdr);
>   	int ret;
> +	u64 p_filesz = elf_phdr_p_filesz(elf, phdr);
> +	u64 p_memsz = elf_phdr_p_memsz(elf, phdr);
>   
>   	/* we care only about PT_LOAD segments */
> -	if (phdr->p_type != PT_LOAD)
> +	if (elf_phdr_p_type(elf, phdr) != PT_LOAD)
>   		return 0;
>   
> -	if (!phdr->p_filesz)
> +	if (!p_filesz)
>   		return 0;
>   
> -	pr_debug("Loading phdr to 0x%p (%i bytes)\n", dst, phdr->p_filesz);
> +	pr_debug("Loading phdr to 0x%p (%llu bytes)\n", dst, p_filesz);
>   
> -	ret = elf_request_region(elf, (resource_size_t)dst, phdr->p_filesz);
> +	ret = elf_request_region(elf, (resource_size_t)dst, p_filesz);
>   	if (ret)
>   		return ret;
>   
> -	memcpy(dst, src, phdr->p_filesz);
> +	memcpy(dst, src, p_filesz);
>   
> -	if (phdr->p_filesz < phdr->p_memsz)
> -		memset(dst + phdr->p_filesz, 0x00,
> -		       phdr->p_memsz - phdr->p_filesz);
> +	if (p_filesz < p_memsz)
> +		memset(dst + p_filesz, 0x00,
> +		       p_memsz - p_filesz);
>   
>   	return 0;
>   }
> @@ -75,14 +77,13 @@ static int load_elf_phdr_segment(struct elf_image *elf, void *src,
>   static int load_elf_image_phdr(struct elf_image *elf)
>   {
>   	void *buf = elf->buf;
> -	Elf32_Ehdr *ehdr = buf;
> -	Elf32_Phdr *phdr = (Elf32_Phdr *)(buf + ehdr->e_phoff);
> +	void *phdr = (void *) (buf + elf_hdr_e_phoff(elf, buf));
>   	int i, ret;
>   
> -	elf->entry = ehdr->e_entry;
> +	elf->entry = elf_hdr_e_entry(elf, buf);
>   
> -	for (i = 0; i < ehdr->e_phnum; ++i) {
> -		void *src = buf + phdr->p_offset;
> +	for (i = 0; i < elf_hdr_e_phnum(elf, buf) ; ++i) {
> +		void *src = buf + elf_phdr_p_offset(elf, phdr);
>   
>   		ret = load_elf_phdr_segment(elf, src, phdr);
>   		/* in case of error elf_load_image() caller should clean up and
> @@ -90,22 +91,22 @@ static int load_elf_image_phdr(struct elf_image *elf)
>   		if (ret)
>   			return ret;
>   
> -		++phdr;
> +		phdr += elf_size_of_phdr(elf);
>   	}
>   
>   	return 0;
>   }
>   
> -static int elf_check_image(void *buf)
> +static int elf_check_image(struct elf_image *elf)
>   {
> -	Elf32_Ehdr *ehdr = (Elf32_Ehdr *)buf;
> -
> -	if (strncmp(buf, ELFMAG, SELFMAG)) {
> +	if (strncmp(elf->buf, ELFMAG, SELFMAG)) {
>   		pr_err("ELF magic not found.\n");
>   		return -EINVAL;
>   	}
>   
> -	if (ehdr->e_type != ET_EXEC) {
> +	elf->class = ((char *) elf->buf)[EI_CLASS];
> +
> +	if (elf_hdr_e_type(elf, elf->buf) != ET_EXEC) {
>   		pr_err("Non EXEC ELF image.\n");
>   		return -ENOEXEC;
>   	}
> @@ -124,7 +125,7 @@ struct elf_image *elf_load_image(void *buf)
>   
>   	elf->buf = buf;
>   
> -	ret = elf_check_image(buf);
> +	ret = elf_check_image(elf);
>   	if (ret)
>   		return ERR_PTR(ret);
>   
> diff --git a/include/elf.h b/include/elf.h
> index 92c8d9c12..633f4992d 100644
> --- a/include/elf.h
> +++ b/include/elf.h
> @@ -400,11 +400,38 @@ static inline void arch_write_notes(struct file *file) { }
>   
>   struct elf_image {
>   	struct list_head list;
> -	unsigned long entry;
> +	u8 class;
> +	u64 entry;
>   	void *buf;
>   };
>   
>   struct elf_image *elf_load_image(void *buf);
>   void elf_release_image(struct elf_image *elf);
>   
> +#define ELF_GET_FIELD(__s, __field, __type) \
> +static inline __type elf_##__s##_##__field(struct elf_image *elf, void *arg) { \
> +	if (elf->class == ELFCLASS32) \
> +		return (__type) ((struct elf32_##__s *) arg)->__field; \
> +	else \
> +		return (__type) ((struct elf64_##__s *) arg)->__field; \
> +}
> +
> +ELF_GET_FIELD(hdr, e_entry, u64)
> +ELF_GET_FIELD(hdr, e_phnum, u16)
> +ELF_GET_FIELD(hdr, e_phoff, u64)
> +ELF_GET_FIELD(hdr, e_type, u16)
> +ELF_GET_FIELD(phdr, p_paddr, u64)
> +ELF_GET_FIELD(phdr, p_filesz, u64)
> +ELF_GET_FIELD(phdr, p_memsz, u64)
> +ELF_GET_FIELD(phdr, p_type, u32)
> +ELF_GET_FIELD(phdr, p_offset, u64)
> +
> +static inline unsigned long elf_size_of_phdr(struct elf_image *elf)
> +{
> +	if (elf->class == ELFCLASS32)
> +		return sizeof(Elf32_Phdr);
> +	else
> +		return sizeof(Elf64_Phdr);
> +}
> +
>   #endif /* _LINUX_ELF_H */
> 

Kind regards,
Oleksij Rempel

-- 
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