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--oformat binary for quick and dirty tests:

as -o a.o a.S ld --oformat binary -o a.out a.o hd a.out 

Gives:

00000000 90 90 |..| 00000002 

Unfortunately this gives a warning:

ld: warning: cannot find entry symbol _start; defaulting to 0000000000400000 

which does not make much sense with binary. It could be silenced with:

.section .text .globl start start: nop nop 

and:

ld -e start --oformat binary -o a.out a.o 

or simply with:

ld -e 0 --oformat binary -o a.out a.o 

which tells ld that the entry point is not _start but the code at address 0.

It is a shame that neither as nor ld can take input / ouptut from stdin / stdout, so no piping.

Proper boot sector

If you are going to to something more serious, the best method is to generate a clean minimal linker script. linker.ld:

SECTIONS { . = 0x7c00; .text : { *(.*) . = 0x1FE; SHORT(0xAA55) } } 

Here we also place the magic bytes with the linker script.

The linker script is important above all to control the output addresses after relocation. Learn more about relocation at: https://stackoverflow.com/a/30507725/895245

Use it as:

as -o a.o a.S ld --oformat binary -o a.img -T linker.ld a.o 

And then you can boot as:

qemu-system-i386 -hda a.img 

Working examples on this repository: https://github.com/cirosantilli/x86-bare-metal-examples/blob/d217b180be4220a0b4a453f31275d38e697a99e0/Makefile

Tested on Binutils 2.24, Ubuntu 14.04.

ld --oformat binary

For quick and dirty tests you can do:

as -o a.o a.S ld --oformat binary -o a.out a.o hd a.out 

Gives:

00000000 90 90 |..| 00000002 

Unfortunately this gives a warning:

ld: warning: cannot find entry symbol _start; defaulting to 0000000000400000 

which does not make much sense with binary. It could be silenced with:

.section .text .globl start start: nop nop 

and:

ld -e start --oformat binary -o a.out a.o 

or simply with:

ld -e 0 --oformat binary -o a.out a.o 

which tells ld that the entry point is not _start but the code at address 0.

It is a shame that neither as nor ld can take input / ouptut from stdin / stdout, so no piping.

Proper boot sector

If you are going to to something more serious, the best method is to generate a clean minimal linker script. linker.ld:

SECTIONS { . = 0x7c00; .text : { *(.*) . = 0x1FE; SHORT(0xAA55) } } 

Here we also place the magic bytes with the linker script.

The linker script is important above all to control the output addresses after relocation. Learn more about relocation at: https://stackoverflow.com/a/30507725/895245

Use it as:

as -o a.o a.S ld --oformat binary -o a.img -T linker.ld a.o 

And then you can boot as:

qemu-system-i386 -hda a.img 

Working examples on this repository: https://github.com/cirosantilli/x86-bare-metal-examples/blob/d217b180be4220a0b4a453f31275d38e697a99e0/Makefile

Tested on Binutils 2.24, Ubuntu 14.04.

--oformat binary for quick and dirty tests:

as -o a.o a.S ld --oformat binary -o a.out a.o hd a.out 

Gives:

00000000 90 90 |..| 00000002 

Unfortunately this gives a warning:

ld: warning: cannot find entry symbol _start; defaulting to 0000000000400000 

which does not make much sense with binary. It could be silenced with:

.section .text .globl start start: nop nop 

and:

ld -e start --oformat binary -o a.out a.o 

or simply with:

ld -e 0 --oformat binary -o a.out a.o 

which tells ld that the entry point is not _start but the code at address 0.

It is a shame that neither as nor ld can take input / ouptut from stdin / stdout, so no piping.

Proper boot sector

If you are going to to something more serious, the best method is to generate a clean minimal linker script. linker.ld:

SECTIONS { . = 0x7c00; .text : { *(.*) . = 0x1FE; SHORT(0xAA55) } } 

Here we also place the magic bytes with the linker script.

The linker script is important above all to control the output addresses after relocation. Learn more about relocation at: http://stackoverflow.com/a/30507725/895245

Use it as:

as -o a.o a.S ld --oformat binary -o a.img -T linker.ld a.o 

And then you can boot as:

qemu-system-i386 -hda a.img 

Working examples on this repository: https://github.com/cirosantilli/x86-bare-metal-examples/blob/d217b180be4220a0b4a453f31275d38e697a99e0/Makefile

Tested on Binutils 2.24, Ubuntu 14.04.

--oformat binary for quick and dirty tests:

as -o a.o a.S ld --oformat binary -o a.out a.o hd a.out 

Gives:

00000000 90 90 |..| 00000002 

Unfortunately this gives a warning:

ld: warning: cannot find entry symbol _start; defaulting to 0000000000400000 

which does not make much sense with binary. It could be silenced with:

.section .text .globl start start: nop nop 

and:

ld -e start --oformat binary -o a.out a.o 

or simply with:

ld -e 0 --oformat binary -o a.out a.o 

which tells ld that the entry point is not _start but the code at address 0.

It is a shame that neither as nor ld can take input / ouptut from stdin / stdout, so no piping.

Proper boot sector

If you are going to to something more serious, the best method is to generate a clean minimal linker script. linker.ld:

SECTIONS { . = 0x7c00; .text : { *(.*) . = 0x1FE; SHORT(0xAA55) } } 

Here we also place the magic bytes with the linker script.

The linker script is important above all to control the output addresses after relocation. Learn more about relocation at: https://stackoverflow.com/a/30507725/895245

Use it as:

as -o a.o a.S ld --oformat binary -o a.img -T linker.ld a.o 

And then you can boot as:

qemu-system-i386 -hda a.img 

Working examples on this repository: https://github.com/cirosantilli/x86-bare-metal-examples/blob/d217b180be4220a0b4a453f31275d38e697a99e0/Makefile

Tested on Binutils 2.24, Ubuntu 14.04.

--oformat binary for quick and dirty tests:

as -o a.o a.S ld --oformat binary -o a.out a.o hd a.out 

Gives:

00000000 90 90 |..| 00000002 

Unfortunately this gives a warning:

ld: warning: cannot find entry symbol _start; defaulting to 0000000000400000 

which does not make much sense with binary. It could be silenced with:

.section .text .globl start start: nop nop 

and:

ld -e start --oformat binary -o a.out a.o 

or simply, using -e 0 option. This tells ld that the entry point is not `_start' but the code at address '0'.

It is a shame that neither as nor ld can take input / ouptut from stdin / stdout, so no piping.

Proper boot sector

If you are going to to something more serious, the best method is to generate a clean minimal linker script. linker.ld:

SECTIONS { . = 0x7c00; .text : { *(.*) . = 0x1FE; SHORT(0xAA55) } } 

Here we also place the magic bytes with the linker script.

The linker script is important above all to control the output addresses after relocation. Learn more about relocation at: http://stackoverflow.com/a/30507725/895245

Use it as:

as -o a.o a.S ld --oformat binary -o a.img -T linker.ld a.o 

And then you can boot as:

qemu-system-i386 -hda a.img 

Working examples on this repository: https://github.com/cirosantilli/x86-bare-metal-examples/blob/d217b180be4220a0b4a453f31275d38e697a99e0/Makefile

Tested on Binutils 2.24, Ubuntu 14.04.

--oformat binary for quick and dirty tests:

as -o a.o a.S ld --oformat binary -o a.out a.o hd a.out 

Gives:

00000000 90 90 |..| 00000002 

Unfortunately this gives a warning:

ld: warning: cannot find entry symbol _start; defaulting to 0000000000400000 

which does not make much sense with binary. It could be silenced with:

.section .text .globl start start: nop nop 

and:

ld -e start --oformat binary -o a.out a.o 

or simply with:

ld -e 0 --oformat binary -o a.out a.o 

which tells ld that the entry point is not _start but the code at address 0.

It is a shame that neither as nor ld can take input / ouptut from stdin / stdout, so no piping.

Proper boot sector

If you are going to to something more serious, the best method is to generate a clean minimal linker script. linker.ld:

SECTIONS { . = 0x7c00; .text : { *(.*) . = 0x1FE; SHORT(0xAA55) } } 

Here we also place the magic bytes with the linker script.

The linker script is important above all to control the output addresses after relocation. Learn more about relocation at: http://stackoverflow.com/a/30507725/895245

Use it as:

as -o a.o a.S ld --oformat binary -o a.img -T linker.ld a.o 

And then you can boot as:

qemu-system-i386 -hda a.img 

Working examples on this repository: https://github.com/cirosantilli/x86-bare-metal-examples/blob/d217b180be4220a0b4a453f31275d38e697a99e0/Makefile

Tested on Binutils 2.24, Ubuntu 14.04.