On Wed, May 05, 2010 at 09:54:18AM +0300, Mika Westerberg wrote:
> This is needed to shut following compiler warning when CONFIG_PROC_VMCORE is
> enabled:
>
> fs/proc/vmcore.c: In function 'parse_crash_elf64_headers':
> fs/proc/vmcore.c:500: warning: passing argument 1 of 'elf_check_arch' from
> incompatible pointer type
>
> ELF32 and ELF64 headers have common fields of same size (namely e_ident and
> e_machine) which are checked in arm_elf_check_arch().
This patch is bogus - and shows the dangers of throwing casts into C code
to shut up warnings without first analysing the code.
Our elf_check_arch() uses:
e_machine
e_entry
e_flags
thusly:
if (x->e_machine != EM_ARM)
if (x->e_entry & 1) {
} else if (x->e_entry & 3)
eflags = x->e_flags;
Now, the Elf32 header looks like this:
typedef struct elf32_hdr{
unsigned char e_ident[EI_NIDENT]; /* 0x00 - 0x0F */
Elf32_Half e_type; /* 0x10 - 0x11 */
Elf32_Half e_machine; /* 0x12 - 0x13 */
Elf32_Word e_version; /* 0x14 - 0x17 */
Elf32_Addr e_entry; /* 0x18 - 0x1b */
Elf32_Off e_phoff; /* 0x1c - 0x1f */
Elf32_Off e_shoff; /* 0x20 - 0x23 */
Elf32_Word e_flags; /* 0x24 - 0x27 */
and Elf64 header:
typedef struct elf64_hdr {
unsigned char e_ident[EI_NIDENT]; /* 0x00 - 0x0F */
Elf64_Half e_type; /* 0x10 - 0x11 */
Elf64_Half e_machine; /* 0x12 - 0x13 */
Elf64_Word e_version; /* 0x14 - 0x17 */
Elf64_Addr e_entry; /* 0x18 - 0x1f */
Elf64_Off e_phoff; /* 0x20 - 0x27 */
Elf64_Off e_shoff; /* 0x28 - 0x2f */
Elf64_Word e_flags; /* 0x30 - 0x33 */
Notice that e_entry and e_flags are different sizes and/or different
offsets, so ARMs elf_check_arch can not work with elf64 headers. So
with an ELF64 header, accessing e_flags will result in actually
accessing the top half of the 64-bit e_phoff, and accessing 32-bit
e_entry will get us the lower half of the 64-bit e_entry.
Now, here's the question: why does this crashkernel stuff want to
parse a 64-bit ELF header on a 32-bit only platform where the crashing
kernel will never generate a 64-bit ELF core file?
