SPIR-V Tools

Overview

The project includes an assembler, disassembler, and validator for SPIR-V, all based on a common static library. The library contains all of the implementation details and is used in the standalone tools whilst also enabling integration into other code bases directly.

Currently, the assembler and disassembler only support the core SPIR-V specification (i.e. nothing Vulkan or OpenCL-specific) and the validator is a work in progress. See the Future Work section for more information.

The repository is maintained by Kenneth Benzie k.benzie@codeplay.com, please submit any merge requests as stated in these instructions.

Build

The project uses CMake to generate platform-specific build configurations. To generate these build files issue the following commands.

mkdir <spirv-dir>/build
cd <spirv-dir>/build
cmake [-G<platform-generator>] ..

Once the build files have been generated, build using your preferred development environment.

CMake Options

• SPIRV_USE_SANITIZER=<sanitizer> - on UNIX platforms with an appropriate version of clang this option enables the use of the sanitizers documented here, this should only be used with a debug build, disabled by default
• SPIRV_COLOR_TERMINAL=ON - enables color console output, enabled by default
• SPIRV_WARN_EVERYTHING=OFF - on UNIX platforms enable the -Weverything compiler front end option, disabled by default
• SPIRV_WERROR=OFF - on UNIX platforms enable the -Werror compiler front end option, disabled by default

Library

Usage

In order to use the library from an application, the include path should point to <spirv-dir>/include, which will enable the application to include the header <spirv-dir>/include/libspirv/libspirv.h then linking against the static library in <spirv-build-dir>/bin/libSPIRV.a or <spirv-build-dir>/bin/SPIRV.lib. The intention is for this to be a C API, however currently it relies on the generated header spirv.h meaning this is currently a C++ API.

• SPIRV - the static library CMake target outputs <spirv-dir>/lib/libSPIRV.a on Linux/Mac or <spirv-dir>/lib/SPIRV.lib on Windows.

Entry Points

There are three main entry points into the library.

• spvTextToBinary implements the assembler functionality.
• spvBinaryToText implements the disassembler functionality.
• spvValidate implements the validator functionality.

Source

In addition to the interface header <spirv-dir>/include/libspirv/libspirv.h the implementation source files reside in <spirv-dir>/source/*.

Tools

Assembler

The standalone assembler is the binary called spirv-as and is located in <spirv-build-dir>/bin/spirv-as. The functionality of the assembler is implemented by the spvTextToBinary library function.

The assembler operates on the textual form.

• spirv-as - the standalone assembler
  • <spirv-dir>/bin/spirv-as

Options

• -o <filename> is used to specify the output file, otherwise this is set to out.spv.

Format

The assembly attempts to adhere to the binary form as closely as possible using text names from that specification. Here is an example.

OpCapability Shader
OpMemoryModel Logical Simple
OpEntryPoint GLCompute %3 "main"
OpExecutionMode %3 LocalSize 64 64 1
OpTypeVoid %1
OpTypeFunction %2 %1
OpFunction %1 %3 None %2
OpLabel %4
OpReturn
OpFunctionEnd

In order to improve the text's readability, the <result-id> generated by an instruction can be moved to the beginning of that instruction and followed by an = sign. This allows us to distinguish between variable defs and uses and locate variable defs more easily. So, the above example can also be written as:

     OpCapability Shader
     OpMemoryModel Logical Simple
     OpEntryPoint GLCompute %3 "main"
     OpExecutionMode %3 LocalSize 64 64 1
%1 = OpTypeVoid
%2 = OpTypeFunction %1
%3 = OpFunction %1 None %2
%4 = OpLabel
     OpReturn
     OpFunctionEnd

Each line encapsulates one and only one instruction, or an OpCode and all of its operands. OpCodes use the names provided in section 3.28 Instructions of the SPIR-V specification, immediate values such as Addressing Model, Memory Model, etc. use the names provided in sections 3.2 Source Language through 3.27 Capability of the SPIR-V specification. Literals strings are enclosed in quotes "<string>" while literal numbers have no special formatting.

ID Definitions & Usage

An ID definition pertains to the <result-id> of an OpCode, and ID usage is any input to an OpCode. All IDs are prefixed with %. To differentiate between defs and uses, we suggest using the second format shown in the above example.

Named IDs

The assembler also supports named IDs, or virtual IDs, which greatly improves the readability of the assembly. The same ID definition and usage prefixes apply. Names must begin with an character in the range [a-z|A-Z]. The following example will result in identical SPIR-V binary as the example above.

          OpCapability Shader
          OpMemoryModel Logical Simple
          OpEntryPoint GLCompute %main "main"
          OpExecutionMode %main LocalSize 64 64 1
  %void = OpTypeVoid
%fnMain = OpTypeFunction %void
  %main = OpFunction %void None %fnMain
%lbMain = OpLabel
          OpReturn
          OpFunctionEnd

Arbitrary Integers

When writing tests it can be useful to emit an invalid 32 bit word into the binary stream at arbitrary positions within the assembly. To specify an arbitrary word into the stream the prefix ! is used, this takes the form !<integer>. Here is an example.

OpCapability !0x0000FF00

Any word in a valid assembly program may be replaced by !<integer> -- even words that dictate how the rest of the instruction is parsed. Consider, for example, the following assembly program:

%4 = OpConstant %1 123 456 789 OpExecutionMode %2 LocalSize 11 22 33
OpExecutionMode %3 InputLines

The words OpConstant, LocalSize, and InputLines may be replaced by random !<integer> values, and the assembler will still assemble an output binary with three instructions. It will not necessarily be valid SPIR-V, but it will faithfully reflect the input text.

You may wonder how the assembler recognizes the instruction structure (including instruction boundaries) in the text with certain crucial words replaced by arbitrary integers. If, say, OpConstant becomes a !<integer> whose value differs from the binary representation of OpConstant (remember that this feature is intended for fine-grain control in SPIR-V testing), the assembler generally has no idea what that value stands for. So how does it know there is exactly one <id> and three number literals following in that instruction, before the next one begins? And if LocalSize is replaced by an arbitrary !<integer>, how does it know to take the next three words (instead of zero or one, both of which are possible in the absence of certainty that LocalSize provided)? The answer is a simple rule governing the parsing of instructions with !<integer> in them:

When a word in the assembly program is a !<integer>, that integer value is emitted into the binary output, and parsing proceeds differently than before: each subsequent word not recognized as an OpCode is treated as an operand (emitted as described below); when a recognizable OpCode is eventually encountered, it begins a new instruction and parsing returns to normal. (If a subsequent OpCode is never found, then the current instruction is last in the generated binary and contains all the words until the end-of-stream as its operands.)

Operands following a !<integer> are interpreted depending on their format:

• If the operand is a number literal, it outputs a word equal to the number.
• If the operand is a string literal, it outputs a sequence of words representing the string as defined in the SPIR-V specification for Literal String.
• If the operand is an ID, it outputs a word equal to the ID's internal number. If no such number exists yet, a unique new one will be generated. (Uniqueness is at the translation-unit level: no other ID in the same translation unit will have the same number.)
• If the operand is a !<integer>, it outputs a word equal to the integer.
• Otherwise, the assembler quits with an error.

Note that this has some interesting consequences, including:

• When an OpCode is replaced by !<integer>, the integer value must encode the instruction's word count, as specified in the physical-layout section of the SPIR-V specification.

• Consecutive instructions may have their OpCode replaced by !<integer> and still produce the expected binary. For example, !262187 %1 %2 "abc" !327739 %1 %3 6 %2 will successfully assemble into SPIR-V declaring a constant and a PrivateGlobal variable.

• Not every word in an assembly program may be replaced by !<integer> without failure. For example, replacing either of the OpExecutionMode OpCodes above will result in an error, because their mode enums are not valid operands in the alternate parsing mode prompted by !<integer>. (It is, however, possible to replace both OpExecutionMode and all mode enums with !<integer> and assemble successfully.)

• When replacing a named ID with !<integer>, it is possible to generate unintentionally valid SPIR-V. If the integer provided happens to equal a number generated for an existing named ID, it will result in a reference to that named ID being output. This may be valid SPIR-V, contrary to the presumed intention of the writer.

• If the next instruction after a !<integer> has the assignment format (described above), then its OpCode cannot also be a !<integer>. The alternate parsing mode cannot handle the assignment format and will complain that = is not a valid operand.

Disassembler

The standalone disassembler is the binary called spirv-dis and is located in <spirv-build-dir>/bin/spirv-dis. The functionality of the disassembler is implemented by the spvBinaryToText library function.

The disassembler operates on the binary form.

• spirv-dis - the standalone disassembler
  • <spirv-dir>/bin/spirv-dis

Options

• -o <filename> is used to specify the output file, otherwise this is set to out.spvasm.
• -p prints the assembly to the console on stdout, this includes colored output on Linux, Windows, and Mac.

Validator

The standalone validator is the binary called spirv-val and is located in <spirv-build-dir>/bin/spirv-val. The functionality of the validator is implemented by the spvValidate library function.

The validator operates on the binary form.

• spirv-val - the standalone validator
  • <spirv-dir>/bin/spirv-val

Options

• -basic performs basic stream validation, currently not implemented.
• -layout performs logical layout validation as described in section 2.16 Validation Rules, currently not implemented.
• -id performs ID validation according to the instruction rules in sections 3.28.1 through 3.28.22, enabled but is a work in progress.
• -capability performs capability validation and or reporting, currently not implemented.

Tests

The project contains a number of tests, implemented in the UnitSPIRV executable, used to drive the development and correctness of the tools, these use the googletest framework. The googletest source is not provided with this project, to enable the tests place the googletest source in the <spirv-dir>/external/googletest directory, rerun CMake if you have already done so previously, CMake will detect the existence of <spirv-dir>/external/googletest then build as normal.

Future Work

• Support extension libraries in spirv-as, spirv-dis, and spirv-val.
• Complete implementation of ID validation rules in spirv-val.
• Implement section 2.16 Validation Rules in spirv-val.
• Implement Capability validation and or report in spirv-val.
• Improve assembly output from spirv-dis.
• Improve diagnostic reports.

Known Issues

• Improve literal parsing in the assembler, currently only decimal integers and floating-point numbers are supported as literal operands and the parser is not contextually aware of the desired width of the operand.

Licence

Copyright (c) 2015 The Khronos Group Inc.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and/or associated documentation files (the "Materials"), to deal in the Materials without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Materials, and to permit persons to whom the Materials are furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Materials.

MODIFICATIONS TO THIS FILE MAY MEAN IT NO LONGER ACCURATELY REFLECTS KHRONOS STANDARDS. THE UNMODIFIED, NORMATIVE VERSIONS OF KHRONOS SPECIFICATIONS AND HEADER INFORMATION ARE LOCATED AT https://www.khronos.org/registry/

THE MATERIALS ARE PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE MATERIALS OR THE USE OR OTHER DEALINGS IN THE MATERIALS.