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package compiler
// This file implements the syscall.Syscall and syscall.Syscall6 instructions as
// compiler builtins.
import (
"strconv"
"golang.org/x/tools/go/ssa"
"tinygo.org/x/go-llvm"
)
// createRawSyscall creates a system call with the provided system call number
// and returns the result as a single integer (the system call result). The
// result is not further interpreted.
func (b *builder) createRawSyscall(call *ssa.CallCommon) (llvm.Value, error) {
num := b.getValue(call.Args[0], getPos(call))
switch {
case b.GOARCH == "amd64" && b.GOOS == "linux":
// Sources:
// https://stackoverflow.com/a/2538212
// https://en.wikibooks.org/wiki/X86_Assembly/Interfacing_with_Linux#syscall
args := []llvm.Value{num}
argTypes := []llvm.Type{b.uintptrType}
// Constraints will look something like:
// "={rax},0,{rdi},{rsi},{rdx},{r10},{r8},{r9},~{rcx},~{r11}"
constraints := "={rax},0"
for i, arg := range call.Args[1:] {
constraints += "," + [...]string{
"{rdi}",
"{rsi}",
"{rdx}",
"{r10}",
"{r8}",
"{r9}",
}[i]
llvmValue := b.getValue(arg, getPos(call))
args = append(args, llvmValue)
argTypes = append(argTypes, llvmValue.Type())
}
// rcx and r11 are clobbered by the syscall, so make sure they are not used
constraints += ",~{rcx},~{r11}"
fnType := llvm.FunctionType(b.uintptrType, argTypes, false)
target := llvm.InlineAsm(fnType, "syscall", constraints, true, false, llvm.InlineAsmDialectIntel, false)
return b.CreateCall(fnType, target, args, ""), nil
case b.GOARCH == "386" && b.GOOS == "linux":
// Sources:
// syscall(2) man page
// https://stackoverflow.com/a/2538212
// https://en.wikibooks.org/wiki/X86_Assembly/Interfacing_with_Linux#int_0x80
args := []llvm.Value{num}
argTypes := []llvm.Type{b.uintptrType}
// Constraints will look something like:
// "={eax},0,{ebx},{ecx},{edx},{esi},{edi},{ebp}"
constraints := "={eax},0"
for i, arg := range call.Args[1:] {
constraints += "," + [...]string{
"{ebx}",
"{ecx}",
"{edx}",
"{esi}",
"{edi}",
"{ebp}",
}[i]
llvmValue := b.getValue(arg, getPos(call))
args = append(args, llvmValue)
argTypes = append(argTypes, llvmValue.Type())
}
fnType := llvm.FunctionType(b.uintptrType, argTypes, false)
target := llvm.InlineAsm(fnType, "int 0x80", constraints, true, false, llvm.InlineAsmDialectIntel, false)
return b.CreateCall(fnType, target, args, ""), nil
case b.GOARCH == "arm" && b.GOOS == "linux":
// Implement the EABI system call convention for Linux.
// Source: syscall(2) man page.
args := []llvm.Value{}
argTypes := []llvm.Type{}
// Constraints will look something like:
// ={r0},0,{r1},{r2},{r7},~{r3}
constraints := "={r0}"
for i, arg := range call.Args[1:] {
constraints += "," + [...]string{
"0", // tie to output
"{r1}",
"{r2}",
"{r3}",
"{r4}",
"{r5}",
"{r6}",
}[i]
llvmValue := b.getValue(arg, getPos(call))
args = append(args, llvmValue)
argTypes = append(argTypes, llvmValue.Type())
}
args = append(args, num)
argTypes = append(argTypes, b.uintptrType)
constraints += ",{r7}" // syscall number
for i := len(call.Args) - 1; i < 4; i++ {
// r0-r3 get clobbered after the syscall returns
constraints += ",~{r" + strconv.Itoa(i) + "}"
}
fnType := llvm.FunctionType(b.uintptrType, argTypes, false)
target := llvm.InlineAsm(fnType, "svc #0", constraints, true, false, 0, false)
return b.CreateCall(fnType, target, args, ""), nil
case b.GOARCH == "arm64" && b.GOOS == "linux":
// Source: syscall(2) man page.
args := []llvm.Value{}
argTypes := []llvm.Type{}
// Constraints will look something like:
// ={x0},0,{x1},{x2},{x8},~{x3},~{x4},~{x5},~{x6},~{x7},~{x16},~{x17}
constraints := "={x0}"
for i, arg := range call.Args[1:] {
constraints += "," + [...]string{
"0", // tie to output
"{x1}",
"{x2}",
"{x3}",
"{x4}",
"{x5}",
}[i]
llvmValue := b.getValue(arg, getPos(call))
args = append(args, llvmValue)
argTypes = append(argTypes, llvmValue.Type())
}
args = append(args, num)
argTypes = append(argTypes, b.uintptrType)
constraints += ",{x8}" // syscall number
for i := len(call.Args) - 1; i < 8; i++ {
// x0-x7 may get clobbered during the syscall following the aarch64
// calling convention.
constraints += ",~{x" + strconv.Itoa(i) + "}"
}
constraints += ",~{x16},~{x17}" // scratch registers
fnType := llvm.FunctionType(b.uintptrType, argTypes, false)
target := llvm.InlineAsm(fnType, "svc #0", constraints, true, false, 0, false)
return b.CreateCall(fnType, target, args, ""), nil
default:
return llvm.Value{}, b.makeError(call.Pos(), "unknown GOOS/GOARCH for syscall: "+b.GOOS+"/"+b.GOARCH)
}
}
// createSyscall emits instructions for the syscall.Syscall* family of
// functions, depending on the target OS/arch.
func (b *builder) createSyscall(call *ssa.CallCommon) (llvm.Value, error) {
switch b.GOOS {
case "linux":
syscallResult, err := b.createRawSyscall(call)
if err != nil {
return syscallResult, err
}
// Return values: r0, r1 uintptr, err Errno
// Pseudocode:
// var err uintptr
// if syscallResult < 0 && syscallResult > -4096 {
// err = -syscallResult
// }
// return syscallResult, 0, err
zero := llvm.ConstInt(b.uintptrType, 0, false)
inrange1 := b.CreateICmp(llvm.IntSLT, syscallResult, llvm.ConstInt(b.uintptrType, 0, false), "")
inrange2 := b.CreateICmp(llvm.IntSGT, syscallResult, llvm.ConstInt(b.uintptrType, 0xfffffffffffff000, true), "") // -4096
hasError := b.CreateAnd(inrange1, inrange2, "")
errResult := b.CreateSelect(hasError, b.CreateSub(zero, syscallResult, ""), zero, "syscallError")
retval := llvm.Undef(b.ctx.StructType([]llvm.Type{b.uintptrType, b.uintptrType, b.uintptrType}, false))
retval = b.CreateInsertValue(retval, syscallResult, 0, "")
retval = b.CreateInsertValue(retval, zero, 1, "")
retval = b.CreateInsertValue(retval, errResult, 2, "")
return retval, nil
case "windows":
// On Windows, syscall.Syscall* is basically just a function pointer
// call. This is complicated in gc because of stack switching and the
// different ABI, but easy in TinyGo: just call the function pointer.
// The signature looks like this:
// func Syscall(trap, nargs, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
// Prepare input values.
var paramTypes []llvm.Type
var params []llvm.Value
for _, val := range call.Args[2:] {
param := b.getValue(val, getPos(call))
params = append(params, param)
paramTypes = append(paramTypes, param.Type())
}
llvmType := llvm.FunctionType(b.uintptrType, paramTypes, false)
fn := b.getValue(call.Args[0], getPos(call))
fnPtr := b.CreateIntToPtr(fn, b.dataPtrType, "")
// Prepare some functions that will be called later.
setLastError := b.mod.NamedFunction("SetLastError")
if setLastError.IsNil() {
llvmType := llvm.FunctionType(b.ctx.VoidType(), []llvm.Type{b.ctx.Int32Type()}, false)
setLastError = llvm.AddFunction(b.mod, "SetLastError", llvmType)
}
getLastError := b.mod.NamedFunction("GetLastError")
if getLastError.IsNil() {
llvmType := llvm.FunctionType(b.ctx.Int32Type(), nil, false)
getLastError = llvm.AddFunction(b.mod, "GetLastError", llvmType)
}
// Now do the actual call. Pseudocode:
// SetLastError(0)
// r1 = trap(a1, a2, a3, ...)
// err = uintptr(GetLastError())
// return r1, 0, err
// Note that SetLastError/GetLastError could be replaced with direct
// access to the thread control block, which is probably smaller and
// faster. The Go runtime does this in assembly.
b.CreateCall(setLastError.GlobalValueType(), setLastError, []llvm.Value{llvm.ConstNull(b.ctx.Int32Type())}, "")
syscallResult := b.CreateCall(llvmType, fnPtr, params, "")
errResult := b.CreateCall(getLastError.GlobalValueType(), getLastError, nil, "err")
if b.uintptrType != b.ctx.Int32Type() {
errResult = b.CreateZExt(errResult, b.uintptrType, "err.uintptr")
}
// Return r1, 0, err
retval := llvm.ConstNull(b.ctx.StructType([]llvm.Type{b.uintptrType, b.uintptrType, b.uintptrType}, false))
retval = b.CreateInsertValue(retval, syscallResult, 0, "")
retval = b.CreateInsertValue(retval, errResult, 2, "")
return retval, nil
default:
return llvm.Value{}, b.makeError(call.Pos(), "unknown GOOS/GOARCH for syscall: "+b.GOOS+"/"+b.GOARCH)
}
}
// createRawSyscallNoError emits instructions for the Linux-specific
// syscall.rawSyscallNoError function.
func (b *builder) createRawSyscallNoError(call *ssa.CallCommon) (llvm.Value, error) {
syscallResult, err := b.createRawSyscall(call)
if err != nil {
return syscallResult, err
}
retval := llvm.ConstNull(b.ctx.StructType([]llvm.Type{b.uintptrType, b.uintptrType}, false))
retval = b.CreateInsertValue(retval, syscallResult, 0, "")
retval = b.CreateInsertValue(retval, llvm.ConstInt(b.uintptrType, 0, false), 1, "")
return retval, nil
}
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