From ab02cbd29f9b9c76d8f7af0d625ac56fcf8d4e75 Mon Sep 17 00:00:00 2001
From: El Mostafa Idrassi <el.mostafa.idrassi@gmail.com>
Date: Tue, 13 Apr 2021 20:08:46 +0000
Subject: [PATCH] runtime: increase maxargs to avoid syscall18 crash when
 called with more than 16 args

Fixes #45524

Change-Id: Id867f45ea98689b73d5b1b141c19317bc7608b05
GitHub-Last-Rev: e9b09fb557dda291fb6cf27c185063c26832a15b
GitHub-Pull-Request: golang/go#45531
Reviewed-on: https://go-review.googlesource.com/c/go/+/309390
Reviewed-by: El Mostafa Idrassi <el.mostafa.idrassi@gmail.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Trust: Alex Brainman <alex.brainman@gmail.com>
Trust: Alberto Donizetti <alb.donizetti@gmail.com>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
---
 src/runtime/sys_windows_amd64.s     |  2 +-
 src/runtime/syscall_windows_test.go | 45 +++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/src/runtime/sys_windows_amd64.s b/src/runtime/sys_windows_amd64.s
index f7250c65a81..68963313297 100644
--- a/src/runtime/sys_windows_amd64.s
+++ b/src/runtime/sys_windows_amd64.s
@@ -8,7 +8,7 @@
 
 // maxargs should be divisible by 2, as Windows stack
 // must be kept 16-byte aligned on syscall entry.
-#define maxargs 16
+#define maxargs 18
 
 // void runtime·asmstdcall(void *c);
 TEXT runtime·asmstdcall<ABIInternal>(SB),NOSPLIT|NOFRAME,$0
diff --git a/src/runtime/syscall_windows_test.go b/src/runtime/syscall_windows_test.go
index 98e426a3d53..5e9694d444c 100644
--- a/src/runtime/syscall_windows_test.go
+++ b/src/runtime/syscall_windows_test.go
@@ -744,6 +744,51 @@ uintptr_t cfunc(callback f, uintptr_t n) {
 	}
 }
 
+func TestSyscall18(t *testing.T) {
+	if _, err := exec.LookPath("gcc"); err != nil {
+		t.Skip("skipping test: gcc is missing")
+	}
+	if runtime.GOARCH != "amd64" {
+		t.Skipf("skipping test: GOARCH=%s", runtime.GOARCH)
+	}
+
+	const src = `
+#include <stdint.h>
+#include <windows.h>
+
+int cfunc(	int a1, int a2, int a3, int a4, int a5, int a6, int a7, int a8, int a9,
+			int a10, int a11, int a12, int a13, int a14, int a15, int a16, int a17, int a18) {
+	return 1;
+}
+`
+	tmpdir := t.TempDir()
+
+	srcname := "mydll.c"
+	err := os.WriteFile(filepath.Join(tmpdir, srcname), []byte(src), 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	outname := "mydll.dll"
+	cmd := exec.Command("gcc", "-shared", "-s", "-Werror", "-o", outname, srcname)
+	cmd.Dir = tmpdir
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("failed to build dll: %v - %v", err, string(out))
+	}
+	dllpath := filepath.Join(tmpdir, outname)
+
+	dll := syscall.MustLoadDLL(dllpath)
+	defer dll.Release()
+
+	proc := dll.MustFindProc("cfunc")
+
+	// proc.Call() will call Syscall18() internally.
+	r, _, err := proc.Call(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
+	if r != 1 {
+		t.Errorf("got %d want 1 (err=%v)", r, err)
+	}
+}
+
 func TestFloatArgs(t *testing.T) {
 	if _, err := exec.LookPath("gcc"); err != nil {
 		t.Skip("skipping test: gcc is missing")