1// SPDX-License-Identifier: Apache-2.0
2// SPDX-FileCopyrightText: 2022 The Ebitengine Authors
3
4//go:build darwin || freebsd || linux || netbsd || windows
5
6package purego
7
8// CDecl marks a function as being called using the __cdecl calling convention as defined in
9// the [MSDocs] when passed to NewCallback. It must be the first argument to the function.
10// This is only useful on 386 Windows, but it is safe to use on other platforms.
11//
12// [MSDocs]: https://learn.microsoft.com/en-us/cpp/cpp/cdecl?view=msvc-170
13type CDecl struct{}
14
15const (
16 maxArgs = 15
17 numOfFloatRegisters = 8 // arm64 and amd64 both have 8 float registers
18)
19
20type syscall15Args struct {
21 fn, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15 uintptr
22 f1, f2, f3, f4, f5, f6, f7, f8 uintptr
23 arm64_r8 uintptr
24}
25
26// SyscallN takes fn, a C function pointer and a list of arguments as uintptr.
27// There is an internal maximum number of arguments that SyscallN can take. It panics
28// when the maximum is exceeded. It returns the result and the libc error code if there is one.
29//
30// In order to call this function properly make sure to follow all the rules specified in [unsafe.Pointer]
31// especially point 4.
32//
33// NOTE: SyscallN does not properly call functions that have both integer and float parameters.
34// See discussion comment https://github.com/ebiten/purego/pull/1#issuecomment-1128057607
35// for an explanation of why that is.
36//
37// On amd64, if there are more than 8 floats the 9th and so on will be placed incorrectly on the
38// stack.
39//
40// The pragma go:nosplit is not needed at this function declaration because it uses go:uintptrescapes
41// which forces all the objects that the uintptrs point to onto the heap where a stack split won't affect
42// their memory location.
43//
44//go:uintptrescapes
45func SyscallN(fn uintptr, args ...uintptr) (r1, r2, err uintptr) {
46 if fn == 0 {
47 panic("purego: fn is nil")
48 }
49 if len(args) > maxArgs {
50 panic("purego: too many arguments to SyscallN")
51 }
52 // add padding so there is no out-of-bounds slicing
53 var tmp [maxArgs]uintptr
54 copy(tmp[:], args)
55 return syscall_syscall15X(fn, tmp[0], tmp[1], tmp[2], tmp[3], tmp[4], tmp[5], tmp[6], tmp[7], tmp[8], tmp[9], tmp[10], tmp[11], tmp[12], tmp[13], tmp[14])
56}