arch/$SRCARCH/kernel/vmlinux.lds

This linker script is the preprocessed output (gcc -E) from arch/$SRCARCH/kernel/vmlinux.lds.S (in a x86 environment from arch/x86/kernel/vmlinux.lds.S).

Minimal linker script

As per a comment in include/asm-generic/vmlinux.lds.h, a minimal linker script has the following (sample) content (different architectures might have special requirements, however):

OUTPUT_FORMAT(...)
OUTPUT_ARCH(...)
ENTRY(...)
SECTIONS
{
     . = START;

     __init_begin = .;
     HEAD_TEXT_SECTION
     INIT_TEXT_SECTION(PAGE_SIZE)
     INIT_DATA_SECTION(...)
     PERCPU_SECTION(CACHELINE_SIZE)
     __init_end = .;

     _stext = .;
     TEXT_SECTION = 0
     _etext = .;

     _sdata = .;
     RO_DATA(PAGE_SIZE)
     RW_DATA(...)
     _edata = .;

     EXCEPTION_TABLE(...)

     BSS_SECTION(0, 0, 0)
     _end = .;

     STABS_DEBUG
     DWARF_DEBUG
     ELF_DETAILS

     DISCARDS           // must be the last
}

[__init_begin, __init_end] is the init section. It may be freed after init.

__init_begin and __init_end should be page aligned, so that the whole .init memory can be freed.

[_stext, _etext] is the text section.

[_sdata, _edata] is the data section.

x86

In my x86/64 environment, the head of the created file (i. e. arch/x86/kernel/vmlinux.lds) looks like

OUTPUT_FORMAT("elf64-x86-64")
OUTPUT_ARCH(i386:x86-64)
ENTRY(phys_startup_64)
jiffies = jiffies_64;
PHDRS {
 text PT_LOAD FLAGS(5);
 data PT_LOAD FLAGS(6);
 percpu PT_LOAD FLAGS(6);
 init PT_LOAD FLAGS(7);
 note PT_NOTE FLAGS(0);
}
SECTIONS
 . = (0xffffffff80000000 + ALIGN(0x1000000, 0x200000));
 phys_startup_64 = ABSOLUTE(startup_64 - 0xffffffff80000000);

The ENTRY(…) command specifies phys_startup_64 as the first instruction to be executed in the output file with this linker script.

Note that phys_startup_64 is defined to be ABSOLUTE(startup_64 - 0xffffffff80000000).

The symbol (or «function») startup_64 is defined in arch/x86/kernel/head_64.S.

The PHDRS command specifies the program headers (which can be printed with objdump -p).

The dot in . = is the location counter.

arch/$SRCARCH/kernel/vmlinux.lds

Minimal linker script

x86

See also