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68 lines
2.5 KiB
68 lines
2.5 KiB
6 years ago
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package compiler
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// This file implements the syscall.Syscall and syscall.Syscall6 instructions as
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// compiler builtins.
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import (
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"go/constant"
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"golang.org/x/tools/go/ssa"
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"tinygo.org/x/go-llvm"
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)
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// emitSyscall emits an inline system call instruction, depending on the target
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// OS/arch.
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func (c *Compiler) emitSyscall(frame *Frame, call *ssa.CallCommon) (llvm.Value, error) {
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num, _ := constant.Uint64Val(call.Args[0].(*ssa.Const).Value)
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switch {
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case c.GOARCH == "amd64" && c.GOOS == "linux":
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// Sources:
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// https://stackoverflow.com/a/2538212
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// https://en.wikibooks.org/wiki/X86_Assembly/Interfacing_with_Linux#syscall
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args := []llvm.Value{llvm.ConstInt(c.uintptrType, num, false)}
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argTypes := []llvm.Type{c.uintptrType}
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// Constraints will look something like:
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// "={rax},0,{rdi},{rsi},{rdx},{r10},{r8},{r9},~{rcx},~{r11}"
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constraints := "={rax},0"
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for i, arg := range call.Args[1:] {
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constraints += "," + [...]string{
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"{rdi}",
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"{rsi}",
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"{rdx}",
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"{r10}",
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"{r8}",
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"{r9}",
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}[i]
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llvmValue, err := c.parseExpr(frame, arg)
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if err != nil {
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return llvm.Value{}, err
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}
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args = append(args, llvmValue)
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argTypes = append(argTypes, llvmValue.Type())
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}
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constraints += ",~{rcx},~{r11}"
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fnType := llvm.FunctionType(c.uintptrType, argTypes, false)
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target := llvm.InlineAsm(fnType, "syscall", constraints, true, false, llvm.InlineAsmDialectIntel)
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syscallResult := c.builder.CreateCall(target, args, "")
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// Return values: r1, r1, err uintptr
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// Pseudocode:
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// var err uintptr
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// if syscallResult < 0 && syscallResult > -4096 {
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// err = -syscallResult
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// }
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// return syscallResult, 0, err
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zero := llvm.ConstInt(c.uintptrType, 0, false)
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inrange1 := c.builder.CreateICmp(llvm.IntSLT, syscallResult, llvm.ConstInt(c.uintptrType, 0, false), "")
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inrange2 := c.builder.CreateICmp(llvm.IntSGT, syscallResult, llvm.ConstInt(c.uintptrType, 0xfffffffffffff000, true), "") // -4096
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hasError := c.builder.CreateAnd(inrange1, inrange2, "")
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errResult := c.builder.CreateSelect(hasError, c.builder.CreateNot(syscallResult, ""), zero, "syscallError")
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retval := llvm.Undef(llvm.StructType([]llvm.Type{c.uintptrType, c.uintptrType, c.uintptrType}, false))
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retval = c.builder.CreateInsertValue(retval, syscallResult, 0, "")
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retval = c.builder.CreateInsertValue(retval, zero, 1, "")
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retval = c.builder.CreateInsertValue(retval, errResult, 2, "")
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return retval, nil
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default:
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return llvm.Value{}, c.makeError(call.Pos(), "unknown GOOS/GOARCH for syscall: "+c.GOOS+"/"+c.GOARCH)
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}
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}
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