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Fix some warnings for size_t, DWORD and int conversions.

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These cases are all in the sp_[non]blocking_{read,write} functions.

On MSVC, these conversions would generate warnings such as:
warning C4267: '=': conversion from 'size_t' to 'DWORD', possible loss of data

The warnings are genuine. There are some places where overflow is technically
possible, due to our use of size_t for sizes in function parameters (unsigned
64-bit on Windows x64), but an enum for return values (typically signed int
and 32-bit, but not guaranteed to be so by the standards), plus the Win32 API
usage of DWORD (unsigned 32-bit) for sizes in ReadFile/WriteFile.

However, overflow in practice would require reading/writing more than 2GB
over a serial port in a single call and is therefore unlikely to be a
real-world concern. I have therefore not tried to catch those cases - but the
places it is possible do now have explicit casts to the smaller types so that
they are more obvious.

We could document and test for a maximum read/write size of INT_MAX, but that
would still depend on the storage of 'enum sp_return' being at least a signed
int, which as I understand it the C standard does not require.

To be absolutely correct we would need a different API where sp_return
was only used for result codes, and the read/write functions took a
pointer to size_t for result sizes.
This commit is contained in:
Martin Ling 2020-01-24 03:11:47 +00:00
parent 4651adb4f6
commit 2149db9e93
1 changed files with 16 additions and 13 deletions
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29
serialport.c
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@ -782,7 +782,8 @@ SP_API enum sp_return sp_blocking_write(struct sp_port *port, const void *buf,
RETURN_INT(0);
#ifdef _WIN32
DWORD remaining_ms, write_size, bytes_written, total_bytes_written = 0;
DWORD remaining_ms, write_size, bytes_written;
size_t remaining_bytes, total_bytes_written = 0;
const uint8_t *write_ptr = (uint8_t *) buf;
bool result;
struct timeout timeout;
@ -805,9 +806,11 @@ SP_API enum sp_return sp_blocking_write(struct sp_port *port, const void *buf,
}
/* Reduce write size if it exceeds the WriteFile limit. */
write_size = count - total_bytes_written;
if (write_size > WRITEFILE_MAX_SIZE)
remaining_bytes = count - total_bytes_written;
if (remaining_bytes > WRITEFILE_MAX_SIZE)
write_size = WRITEFILE_MAX_SIZE;
else
write_size = (DWORD) remaining_bytes;
/* Start write. */
@ -837,7 +840,7 @@ SP_API enum sp_return sp_blocking_write(struct sp_port *port, const void *buf,
total_bytes_written += bytes_written;
}
RETURN_INT(total_bytes_written);
RETURN_INT((int) total_bytes_written);
#else
size_t bytes_written = 0;
unsigned char *ptr = (unsigned char *) buf;
@ -911,7 +914,7 @@ SP_API enum sp_return sp_nonblocking_write(struct sp_port *port,
RETURN_INT(0);
#ifdef _WIN32
DWORD buf_bytes;
size_t buf_bytes;
/* Check whether previous write is complete. */
if (port->writing) {
@ -941,7 +944,7 @@ SP_API enum sp_return sp_nonblocking_write(struct sp_port *port,
memcpy(port->write_buf, buf, buf_bytes);
/* Start asynchronous write. */
if (WriteFile(port->hdl, port->write_buf, buf_bytes, NULL, &port->write_ovl) == 0) {
if (WriteFile(port->hdl, port->write_buf, (DWORD) buf_bytes, NULL, &port->write_ovl) == 0) {
if (GetLastError() == ERROR_IO_PENDING) {
if ((port->writing = !HasOverlappedIoCompleted(&port->write_ovl)))
DEBUG("Asynchronous write completed immediately");
@ -955,7 +958,7 @@ SP_API enum sp_return sp_nonblocking_write(struct sp_port *port,
DEBUG("All bytes written immediately");
RETURN_INT(buf_bytes);
RETURN_INT((int) buf_bytes);
#else
/* Returns the number of bytes written, or -1 upon failure. */
ssize_t written = write(port->fd, buf, count);
@ -1013,7 +1016,7 @@ SP_API enum sp_return sp_blocking_read(struct sp_port *port, void *buf,
RETURN_INT(0);
#ifdef _WIN32
DWORD bytes_read = 0;
DWORD bytes_read;
/* Set timeout. */
if (port->timeouts.ReadIntervalTimeout != 0 ||
@ -1027,9 +1030,9 @@ SP_API enum sp_return sp_blocking_read(struct sp_port *port, void *buf,
}
/* Start read. */
if (ReadFile(port->hdl, buf, count, NULL, &port->read_ovl)) {
if (ReadFile(port->hdl, buf, (DWORD) count, NULL, &port->read_ovl)) {
DEBUG("Read completed immediately");
bytes_read = count;
bytes_read = (DWORD) count;
} else if (GetLastError() == ERROR_IO_PENDING) {
DEBUG("Waiting for read to complete");
if (GetOverlappedResult(port->hdl, &port->read_ovl, &bytes_read, TRUE) == 0)
@ -1041,7 +1044,7 @@ SP_API enum sp_return sp_blocking_read(struct sp_port *port, void *buf,
TRY(restart_wait_if_needed(port, bytes_read));
RETURN_INT(bytes_read);
RETURN_INT((int) bytes_read);
#else
size_t bytes_read = 0;
@ -1144,7 +1147,7 @@ SP_API enum sp_return sp_blocking_read_next(struct sp_port *port, void *buf,
/* Loop until we have at least one byte, or timeout is reached. */
while (bytes_read == 0) {
/* Start read. */
if (ReadFile(port->hdl, buf, count, &bytes_read, &port->read_ovl)) {
if (ReadFile(port->hdl, buf, (DWORD) count, &bytes_read, &port->read_ovl)) {
DEBUG("Read completed immediately");
} else if (GetLastError() == ERROR_IO_PENDING) {
DEBUG("Waiting for read to complete");
@ -1250,7 +1253,7 @@ SP_API enum sp_return sp_nonblocking_read(struct sp_port *port, void *buf,
}
/* Do read. */
if (ReadFile(port->hdl, buf, count, NULL, &port->read_ovl) == 0)
if (ReadFile(port->hdl, buf, (DWORD) count, NULL, &port->read_ovl) == 0)
if (GetLastError() != ERROR_IO_PENDING)
RETURN_FAIL("ReadFile() failed");