llvm

Library for interacting with LLVM IR in pure Go.

Introduction

• Introductory blog post "LLVM IR and Go"
• Our Document

Installation

go get github.com/llir/llvm/...

Versions

Map between llir/llvm tagged releases and LLVM release versions.

• llir/llvm v0.3.7: LLVM 15.0 (yet to be released)
• llir/llvm v0.3.6: LLVM 14.0
• llir/llvm v0.3.5: LLVM 13.0
• llir/llvm v0.3.4: LLVM 12.0
• llir/llvm v0.3.3: LLVM 11.0
• llir/llvm v0.3.2: LLVM 10.0
• llir/llvm v0.3.0: LLVM 9.0

Users

• decomp: LLVM IR to Go decompiler by @decomp.
• geode: Geode to LLVM IR compiler by @nickwanninger.
• leaven: LLVM IR to Go decompiler by @andybalholm.
• slate: Slate to LLVM IR compiler by @nektro.
• tre: Go to LLVM IR compiler by @zegl.
• uc: µC to LLVM IR compiler by @sangisos and @mewmew.
• B++: B++ to LLVM IR compiler by @Nv7-Github.

Usage

Input example, parsing LLVM IR assembly

Example usage in GoDoc.

// This example parses an LLVM IR assembly file and pretty-prints the data types
// of the parsed module to standard output.
package main

import (
	"log"

	"github.com/kr/pretty"
	"github.com/llir/llvm/asm"
)

func main() {
	// Parse the LLVM IR assembly file `foo.ll`.
	m, err := asm.ParseFile("foo.ll")
	if err != nil {
		log.Fatalf("%+v", err)
	}
	// Pretty-print the data types of the parsed LLVM IR module.
	pretty.Println(m)
}

Output examples, producing LLVM IR assembly

Hello, World

Example usage in GoDoc.

// This example produces LLVM IR generating "Hello, World" output.

package main

import (
	"fmt"

	"github.com/llir/llvm/ir"
	"github.com/llir/llvm/ir/constant"
	"github.com/llir/llvm/ir/types"
)

func main() {
	// Create a new LLVM IR module.
	m := ir.NewModule()
	hello := constant.NewCharArrayFromString("Hello, world!\n\x00")
	str := m.NewGlobalDef("str", hello)
	// Add external function declaration of puts.
	puts := m.NewFunc("puts", types.I32, ir.NewParam("", types.NewPointer(types.I8)))
	main := m.NewFunc("main", types.I32)
	entry := main.NewBlock("")
	// Cast *[15]i8 to *i8.
	zero := constant.NewInt(types.I64, 0)
	gep := constant.NewGetElementPtr(hello.Typ, str, zero, zero)
	entry.NewCall(puts, gep)
	entry.NewRet(constant.NewInt(types.I32, 0))
	fmt.Println(m)
}

Pseudo Random-Number Generator

Example usage in GoDoc.

// This example produces LLVM IR code equivalent to the following C code, which
// implements a pseudo-random number generator.
//
//    int abs(int x);
//
//    int seed = 0;
//
//    // ref: https://en.wikipedia.org/wiki/Linear_congruential_generator
//    //    a = 0x15A4E35
//    //    c = 1
//    int rand(void) {
//       seed = seed*0x15A4E35 + 1;
//       return abs(seed);
//    }
package main

import (
	"fmt"

	"github.com/llir/llvm/ir"
	"github.com/llir/llvm/ir/constant"
	"github.com/llir/llvm/ir/types"
)

func main() {
	// Create convenience types and constants.
	i32 := types.I32
	zero := constant.NewInt(i32, 0)
	a := constant.NewInt(i32, 0x15A4E35) // multiplier of the PRNG.
	c := constant.NewInt(i32, 1)         // increment of the PRNG.

	// Create a new LLVM IR module.
	m := ir.NewModule()

	// Create an external function declaration and append it to the module.
	//
	//    int abs(int x);
	abs := m.NewFunc("abs", i32, ir.NewParam("x", i32))

	// Create a global variable definition and append it to the module.
	//
	//    int seed = 0;
	seed := m.NewGlobalDef("seed", zero)

	// Create a function definition and append it to the module.
	//
	//    int rand(void) { ... }
	rand := m.NewFunc("rand", i32)

	// Create an unnamed entry basic block and append it to the `rand` function.
	entry := rand.NewBlock("")

	// Create instructions and append them to the entry basic block.
	tmp1 := entry.NewLoad(i32, seed)
	tmp2 := entry.NewMul(tmp1, a)
	tmp3 := entry.NewAdd(tmp2, c)
	entry.NewStore(tmp3, seed)
	tmp4 := entry.NewCall(abs, tmp3)
	entry.NewRet(tmp4)

	// Print the LLVM IR assembly of the module.
	fmt.Println(m)
}

Analysis example, processing LLVM IR

Example usage in GoDoc.

// This example program analyses an LLVM IR module to produce a callgraph in
// Graphviz DOT format.
package main

import (
	"fmt"
	"strings"

	"github.com/llir/llvm/asm"
	"github.com/llir/llvm/ir"
)

func main() {
	// Parse LLVM IR assembly file.
	m, err := asm.ParseFile("foo.ll")
	if err != nil {
		panic(err)
	}
	// Produce callgraph of module.
	callgraph := genCallgraph(m)
	// Output callgraph in Graphviz DOT format.
	fmt.Println(callgraph)
}

// genCallgraph returns the callgraph in Graphviz DOT format of the given LLVM
// IR module.
func genCallgraph(m *ir.Module) string {
	buf := &strings.Builder{}
	buf.WriteString("digraph {\n")
	// For each function of the module.
	for _, f := range m.Funcs {
		// Add caller node.
		caller := f.Ident()
		fmt.Fprintf(buf, "\t%q\n", caller)
		// For each basic block of the function.
		for _, block := range f.Blocks {
			// For each non-branching instruction of the basic block.
			for _, inst := range block.Insts {
				// Type switch on instruction to find call instructions.
				switch inst := inst.(type) {
				case *ir.InstCall:
					callee := inst.Callee.Ident()
					// Add edges from caller to callee.
					fmt.Fprintf(buf, "\t%q -> %q\n", caller, callee)
				}
			}
			// Terminator of basic block.
			switch term := block.Term.(type) {
			case *ir.TermRet:
				// do something.
				_ = term
			}
		}
	}
	buf.WriteString("}")
	return buf.String()
}

License

The llir/llvm project is dual-licensed to the public domain and under a zero-clause BSD license. You may choose either license to govern your use of llir/llvm.