SPI::transfer is defined in spi.h and spi.cpp

[JojoS62]

Description of defect

while examing problems with the current SPI implementation in #15115, I found that SPI::transfer is defined twice. Is this intended or is just not removed during compiling?

The transfer function is declared as template including code:

mbed-os/drivers/include/drivers/SPI.h

Lines 258 to 266 in 07e119b

	template<typename Type>
	int transfer(const Type *tx_buffer, int tx_length, Type *rx_buffer, int rx_length, const event_callback_t &callback, int event = SPI_EVENT_COMPLETE)
	{
	if (spi_active(&_peripheral->spi)) {
	return queue_transfer(tx_buffer, tx_length, rx_buffer, rx_length, sizeof(Type) * 8, callback, event);
	}
	start_transfer(tx_buffer, tx_length, rx_buffer, rx_length, sizeof(Type) * 8, callback, event);
	return 0;
	}

And also as code in :

mbed-os/drivers/source/SPI.cpp

Lines 281 to 288 in 07e119b

	int SPI::transfer(const void *tx_buffer, int tx_length, void *rx_buffer, int rx_length, unsigned char bit_width, const event_callback_t &callback, int event)
	{
	if (spi_active(&_peripheral->spi)) {
	return queue_transfer(tx_buffer, tx_length, rx_buffer, rx_length, bit_width, callback, event);
	}
	start_transfer(tx_buffer, tx_length, rx_buffer, rx_length, bit_width, callback, event);
	return 0;
	}

I can remove the code from SPI.cpp and it still compiles fine because its created from the header.

Target(s) affected by this defect ?

Targets with ASYNC_SPI

Toolchain(s) (name and version) displaying this defect ?

gcc 10.2.1

What version of Mbed-os are you using (tag or sha) ?

mbed-os-6.15.0

What version(s) of tools are you using. List all that apply (E.g. mbed-cli)

mbed-tools 7.44.0

How is this defect reproduced ?

with code that uses SPI.transfer()

[JojoS62]

I got it, the function signatures are different.
When the buffer pointer is used, then the bit_width is calculated by size_of(TYPE).
In case of a generic void pointer, the size must be provided.
This can produce nasty problems when casting the buffer pointer to (char*).