QEMU Windows COM port setup dialog always invoked and fails if none is available (USB or virtual serial port hardware)
Host environment
- Operating system: Windows 10
- OS/kernel version: 22H2
- Architecture: x64
- QEMU flavor: qemu-system-arm
- QEMU version: QEMU emulator version 8.2.94 (v9.0.0-rc4-dirty)
- QEMU command line:
r:/apps/qemu9/qemu-system-arm -gdb \\.\CNCA8 -serial mon:stdio -m 16M -nographic -machine mps2-an500 -cpu cortex-m7 -S -kernel firmware.elf
## Description of problem
The Windows backend serial port in `chardev/char-win.c` always calls `CommConfigDialog()`. This should display a COM port configuration dialog which does (and can) not persist the COM port settings. If the COM port does not support this action (see https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-commconfigdialoga) then the function fails.
## Steps to reproduce
1. Currently not possible with QEMU releases as QEMU does not recognize extended COM port specifications like `\\.\COM19` or `\\.\CNCA0`
## Additional information
See https://support.microsoft.com/en-gb/topic/howto-specify-serial-ports-larger-than-com9-db9078a5-b7b6-bf00-240f-f749ebfd913e for details on COM port filenames.
I have a patch which 'fixes' this problem by setting the nominated COM port to defaults of `115200,8,N,0` which seems perfectly sensible in 2024. Please contact me for more details. A git diff shown below (with extensive error reporting)
N.B. Markodown will destroy formatting!
diff --git a/chardev/char-win.c b/chardev/char-win.c index d4fb44c4dc..a05896ffe9 100644 --- a/chardev/char-win.c +++ b/chardev/char-win.c @@ -96,12 +96,24 @@ int win_chr_serial_init(Chardev *chr, const char *filename, Error **errp) s->file = CreateFile(filename, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_FLAG_OVERLAPPED, 0); if (s->file == INVALID_HANDLE_VALUE) {
-
{
-
char buffer[1024] = { 0 };
-
DWORD dw = GetLastError();
-
sprintf_s(buffer, 1024, "%s(%d) Error: %d 0x%x %s\r\n", __FILE__, __LINE__, dw, dw, filename);
-
OutputDebugString(buffer);
-
} error_setg_win32(errp, GetLastError(), "Failed CreateFile"); s->file = NULL; goto fail;
}
if (!SetupComm(s->file, NRECVBUF, NSENDBUF)) {
-
{
-
char buffer[1024] = { 0 };
-
DWORD dw = GetLastError();
-
sprintf_s(buffer, 1024, "%s(%d) Error: %d 0x%x %s\r\n", __FILE__, __LINE__, dw, dw, filename);
-
OutputDebugString(buffer);
-
} error_setg(errp, "Failed SetupComm"); goto fail;
} @@ -110,9 +122,31 @@ int win_chr_serial_init(Chardev *chr, const char *filename, Error **errp) size = sizeof(COMMCONFIG); GetDefaultCommConfig(filename, &comcfg, &size); comcfg.dcb.DCBlength = sizeof(DCB);
- CommConfigDialog(filename, NULL, &comcfg);
+#if 1
- // JME hardwire. There seems to be no mechanism to simply specify serial port options
- comcfg.dcb.BaudRate = 115200;
- comcfg.dcb.Parity = NOPARITY;
- comcfg.dcb.StopBits = ONESTOPBIT;
- comcfg.dcb.ByteSize = 8; +#else
- {
-
BOOL ret = CommConfigDialog(filename, NULL, &comcfg);
-
if (!ret)
-
{
-
char buffer[1024] = { 0 };
-
DWORD dw = GetLastError();
-
sprintf_s(buffer, 1024, "%s(%d) Error: %d 0x%x %s\r\n", __FILE__, __LINE__, dw, dw, filename);
-
OutputDebugString(buffer);
-
}
- } +#endif if (!SetCommState(s->file, &comcfg.dcb)) {
-
{
-
char buffer[1024]={0};
-
DWORD dw = GetLastError();
-
sprintf_s(buffer,1024,"%s(%d) Error: %d 0x%x %s\r\n",__FILE__,__LINE__,dw,dw, filename);
-
OutputDebugString(buffer);
-
} error_setg(errp, "Failed SetCommState"); goto fail;
/label ~"kind::Bug"