SPV file format: module and instructions

The Khronos Group defines SPIR-V in its SPIR-V Specification; this page follows the unified edition, version 1.6, revision 8, which covers every version from 1.0. A module is a single linear stream of 32-bit words. Only the major and minor version are recorded in a module; the major version has been fixed at 1.

Header

Word	Byte offset	Field	Meaning
0	`0`	Magic number	`0x07230203`.
1	`4`	Version	Bytes, from high-order to low-order: 0, major, minor, 0. Version 1.3 is `0x00010300`, 1.6 is `0x00010600`.
2	`8`	Generator	Identifies the tool that wrote the module; see generators. It does not change the meaning of the module and may be 0, but a non-zero value is encouraged.
3	`12`	Bound	Every ID in the module satisfies 0 < ID < bound; smaller is better.
4	`16`	Schema	Reserved for an instruction schema; 0.
5	`20`	—	First word of the instruction stream.

The specification defines a module as words, not bytes. When it is stored as bytes, as in a .spv file, the magic number’s byte order shows the file’s byte order: a little-endian file starts 03 02 23 07.

Instruction encoding

Word	Contents
0	High 16 bits: the word count, the instruction’s total length in words including this word. Low 16 bits: the opcode (see opcodes).
1…	An optional result type ID, an optional result ID, then the operands. How many operands there are follows from the word count.

Because every instruction states its own length, a reader can step over instructions it does not understand. Operands that are not IDs are literals or values from the enumerations.

Literal strings

A string operand is NUL-terminated, case-sensitive UTF-8. Its bytes are packed four to a word, the first byte in the lowest-order 8 bits. The last word holds the NUL, and any bytes after it in that word are 0. For example main takes two words: 0x6E69616D (m a i n) and 0x00000000.

Logical layout

Instructions must appear in this order:

All OpCapability instructions.
Optional OpExtension instructions.
Optional OpExtInstImport instructions.
The single required OpMemoryModel.
All entry points (OpEntryPoint).
All execution modes (OpExecutionMode, OpExecutionModeId).
Debug instructions, in this order: OpString, OpSourceExtension, OpSource and OpSourceContinued (without forward references); then OpName and OpMemberName; then OpModuleProcessed.
All annotations (decorations).
Type declarations, constants and global variables (OpVariable not in the Function storage class).
Function declarations: OpFunction, OpFunctionParameter, OpFunctionEnd.
Function definitions: OpFunction, OpFunctionParameter, the blocks, OpFunctionEnd.

Generators

The high 16 bits of the generator word are a tool ID registered with Khronos (unique across all SPIR-V generators); the low 16 bits are left to the tool, usually a version number. The registry in spir-v.xml lists:

ID	Vendor	Tool
0	Khronos	—
1	LunarG	—
2	Valve	—
3	Codeplay	—
4	NVIDIA	—
5	ARM	—
6	Khronos	LLVM/SPIR-V Translator
7	Khronos	SPIR-V Tools Assembler
8	Khronos	Glslang Reference Front End
9	Qualcomm	—
10	AMD	—
11	Intel	—
12	Imagination	—
13	Google	Shaderc over Glslang
14	Google	spiregg
15	Google	rspirv
16	X-LEGEND	Mesa3D GLSL-IR/SPIR-V Translator
17	Khronos	SPIR-V Tools Linker
18	Wine	VKD3D Shader Compiler
19	Tellusim	Clay Shader Compiler
20	W3C WebGPU Group	WHLSL Shader Translator
21	Google	Clspv
22	LLVM	MLIR SPIR-V Serializer
23	Google	Tint Compiler
24	Google	ANGLE Shader Compiler
25	Netease Games	Messiah Shader Compiler
26	Xenia	Xenia Emulator Microcode Translator
27	Embark Studios	Rust GPU Compiler Backend
28	gfx-rs community	Naga
29	Mikkosoft Productions	MSP Shader Compiler
30	SpvGenTwo community	SpvGenTwo SPIR-V IR Tools
31	Google	Skia SkSL
32	TornadoVM	Beehive SPIRV Toolkit
33	DragonJoker	ShaderWriter
34	Rayan Hatout	SPIRVSmith
35	Saarland University	Shady
36	Taichi Graphics	Taichi
37	heroseh	Hero C Compiler
38	Meta	SparkSL
39	SirLynix	Nazara ShaderLang Compiler
40	Khronos	Slang Compiler
41	Zig Software Foundation	Zig Compiler
42	Rendong Liang	spq
43	LLVM	LLVM SPIR-V Backend
44	Robert Konrad	Kongruent
45	Kitsunebi Games	Nuvk SPIR-V Emitter and DLSL compiler
46	Nintendo	—
47	ARM	—
48	Goopax	—
49	Icyllis Milica	Arc3D Shader Compiler
50	Isochron	Pred
51	apilatosba	Apila Jai Compiler

“—” means the ID is registered to the vendor without a tool name.

Sources

SPIR-V Specification – Khronos, unified version 1.6 revision 8: sections 1.3 (versions), 2.2 (literal strings), 2.3 (physical layout) and 2.4 (logical layout)
spir-v.xml – Khronos SPIRV-Headers: the registered generator tool IDs

The byte-order remark about .spv files follows from the magic number’s value; the string example was worked out for this page.