Jeremy Fitzhardinge <jeremy at goop.org> writes:
> Eric W. Biederman wrote:
>> To pick a nit. Bootloaders should never use ELF sections only ELF segments.
>> In particular that is what the note segment is for.
>>
>
> Yes, that's definitely the right answer in this case. I'll give this a spin and
> see how it looks.
>
>> Just to verify, the goal when we are done is to have one binary
>> kernel that will run on real hardware, under Xen, and paravirtualized VMware,
>> and on any other hypervisor that comes along.
>>
>
> Correct. Though as you point out, you may need both the bzImage and the vmlinux
> files from a particular build for file-format reasons.
I don't expect that to be the case long term.
You can put an ELF header where the x86 boot sector used to live.
I should be submitting patches for that in a week or so.
>> As I understand it. That goal requires a bzImage with an ELF header :)
>> Which we will have shortly.
>>
>
> OK. Is there some documentation or discussion I can look at to see how that
> would fit together? What's actually in the ELF header?
A quick synopsis:
The true elf header.
typedef struct
{
unsigned char e_ident[EI_NIDENT]; /* Magic number and other info */
Elf32_Half e_type; /* Object file type */
Elf32_Half e_machine; /* Architecture */
Elf32_Word e_version; /* Object file version */
Elf32_Addr e_entry; /* Entry point virtual address */
Elf32_Off e_phoff; /* Program header table file offset */
Elf32_Off e_shoff; /* Section header table file offset */
Elf32_Word e_flags; /* Processor-specific flags */
Elf32_Half e_ehsize; /* ELF header size in bytes */
Elf32_Half e_phentsize; /* Program header table entry size */
Elf32_Half e_phnum; /* Program header table entry count */
Elf32_Half e_shentsize; /* Section header table entry size */
Elf32_Half e_shnum; /* Section header table entry count */
Elf32_Half e_shstrndx; /* Section header string table index */
} Elf32_Ehdr;
A program segment header.
typedef struct
{
Elf32_Word p_type; /* Segment type */
Elf32_Off p_offset; /* Segment file offset */
Elf32_Addr p_vaddr; /* Segment virtual address */
Elf32_Addr p_paddr; /* Segment physical address */
Elf32_Word p_filesz; /* Segment size in file */
Elf32_Word p_memsz; /* Segment size in memory */
Elf32_Word p_flags; /* Segment flags */
Elf32_Word p_align; /* Segment alignment */
} Elf32_Phdr;
The header of an elf Note.
typedef struct
{
Elf32_Word n_namesz; /* Length of the note's name. */
Elf32_Word n_descsz; /* Length of the note's descriptor. */
Elf32_Word n_type; /* Type of the note. */
} Elf32_Nhdr;
Pretty simple and easy to work with. The structures above are the only
ones a bootloader should care about.
The LSB should have links to the full documentation.
Eric
