multiboot elf loader fails if file class (32/64bit) is different than host

[Thomas Haller]

Hello GRUB developers,

i'am trying to boot a self developed kernel with grub in bochs. The kernel
image is an x86_64 elf file. "readelf -h" output is:

ELF Header:
  Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF64
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           Advanced Micro Devices X86-64
  Version:                           0x1
  Entry point address:               0x10000c
  Start of program headers:          64 (bytes into file)
  Start of section headers:          24784 (bytes into file)
  Flags:                             0x0
  Size of this header:               64 (bytes)
  Size of program headers:           56 (bytes)
  Number of program headers:         2
  Size of section headers:           64 (bytes)
  Number of section headers:         11
  Section header string table index: 10

I'am using grub 1.99 compiled for i386-pc. The output after "multiboot
/boot/kernel" is "error: invalid offset in section header.". I found out
that grub uses the 32bit Elf_Shdr structure even if the file is 64bit. My
patch proposal is to apply the same handling as Elf_Ehdr or Elf_Phdr to
Elf_Shdr too.

diff -ruN grub-1.99/grub-core/loader/multiboot_elfxx.c
grub-1.99_new/grub-core/loader/multiboot_elfxx.c
--- grub-1.99/grub-core/loader/multiboot_elfxx.c        2010-12-01
15:45:43.000000000 +0100
+++ grub-1.99_new/grub-core/loader/multiboot_elfxx.c    2011-09-20
15:57:02.000000000 +0200
@@ -22,12 +22,14 @@
 # define ELFCLASSXX    ELFCLASS32
 # define Elf_Ehdr      Elf32_Ehdr
 # define Elf_Phdr      Elf32_Phdr
+# define Elf_Shdr      Elf32_Shdr
 #elif defined(MULTIBOOT_LOAD_ELF64)
 # define XX            64
 # define E_MACHINE     MULTIBOOT_ELF64_MACHINE
 # define ELFCLASSXX    ELFCLASS64
 # define Elf_Ehdr      Elf64_Ehdr
 # define Elf_Phdr      Elf64_Phdr
+# define Elf_Shdr      Elf64_Shdr
 #else
 #error "I'm confused"
 #endif
@@ -223,3 +225,4 @@
 #undef ELFCLASSXX
 #undef Elf_Ehdr
 #undef Elf_Phdr
+#undef Elf_Shdr

Thanks in advance,
Thomas Haller