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/*
* This linker script is used to drive the link step of the kernel, by e.g.
* forcing the linker to use specific addresses when allocating space for
* sections and symbols.
*
* It assumes flat physical memory (RAM) starting at 0, of size 64MB,
* of which only "upper memory", starting at 1MB, is used.
*
* On x86, the first 1MB of physical memory is where legacy BIOS mappings
* are mapped. Completely skip that region for convenience.
*
* For a map of lower memory, see http://wiki.osdev.org/Memory_Map_(x86).
*/
/*
* Override the default entry point. This sets the address of the first
* instruction run when the boot loader passes control to the kernel.
*/
ENTRY(boot_start)
/*
* The memory command is used to describe regions of memory. Here, a single
* region of RAM is defined. Adding another region, such as the video RAM
* at 0xa0000, would allow other commands in this script to allocate symbols
* out of that region.
*
* Describing memory regions is optional. It is best used when building for
* known devices with a specific memory layout.
*/
MEMORY
{
RAM : ORIGIN = 1M, LENGTH = 63M
}
/*
* The program headers define segments in the ELF image. they are used to
* fix properties on sections mapped to segments. Here, the PT_LOAD flag
* tells the boot loader that a segment must actually be loaded from the
* ELF image to memory. Some sections, such as most debugging sections, are
* normally not loaded to memory. FLAGS are used to set Unix-like
* permissions to a segment, so that a value of 4 means the segment may
* only contain read-only non-executable data, 5 (4 + 1) means read-only
* executable data (normally instructions), and 6 (4 + 2) means read-write
* non-executable data.
*
* The hdr segment is meant to contain the multiboot header. The name "text"
* is the historical name used to refer to instructions.
*
* See https://sourceware.org/binutils/docs-2.29/ld/index.html.
*/
PHDRS
{
hdr PT_LOAD FLAGS(4);
text PT_LOAD FLAGS(5);
data PT_LOAD FLAGS(6);
}
/*
* Sections define how the image data are partitioned.
*
* Common sections include :
*
* - .text
* The code section.
* - .data
* The section for initialized data (e.g. static int var = 123;).
* - .bss
* The section for uninitialized data (e.g. static int var;). Its name
* is historical and means "Block Started by Symbol". The .bss section
* is special in that it takes no space in the kernel image, because
* it's filled with bytes of value 0. Its size in memory is stored
* in the ELF file, and in this case, the boot loader initializes the
* memory for the .bss section.
*
* Here, an additional section is used to store the multiboot header, and
* any section for read-only data produced by the compiler is forced into
* the .data section.
*
* Sections are allocated out of the RAM memory region, and mapped to heir
* corresponding program headers segment.
*
* See https://sourceware.org/binutils/docs-2.29/ld/Input-Section-Basics.html#Input-Section-Basics
* for more information about the syntax used below.
*/
SECTIONS
{
.hdr : {
*(.hdr)
} > RAM : hdr
.text : {
*(.text*)
} > RAM : text
.data : {
*(.rodata*)
*(.data*)
} > RAM : data
.bss : {
*(.bss)
} > RAM : data
/*
* The .eh_frame section is used by DWARF tools to unwind the stack,
* allowing software to dump stack traces. Although this section could
* safely be left in the kernel image, it may confuse people who
* disassemble it.
*/
/DISCARD/ : {
*(.eh_frame)
}
}
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