When standard C libraries are added to BASELIBS to group them together with all other modules, there are multiple definitions for the putchar function. The one that is defined writing to the UART as standard output and the one that is provided by the standard C libraries. To solve this symbol conflict, putchar and getchar functions that use the UART as standard output/input are renamed to __wrap_putchar and __wrap_getchar and the linker options are extended by -Wl,-wrap option.
When linking an application, symbol pthread_setcancelstate is not known in standard C libraries, even if the pthread module is linked. This is because the pthread module is grouped with all other modules, but not with the default C libraries when they are added to LINK_FLAGS. Therefore, standard C libraries have to be added also to BASELIBS to group them with all other modules.
Fixes the problem that the compilation of an applications can throw unknown symbol errors for functions that aren't use at all. Thus, it is possible to remove the warning for unknown symbols and the compilation can abort if there are real unknown symbols.
The length field in an MQTT packet carries the _total_ length of the
packet. If it is below 256 (i.e. fits in one byte) only one byte is
used for the length field. If it is larger than that 3 bytes are used,
with the first byte having the value `0x01` and the remaining bytes
representing the length in as a 2 byte unsigned integer in network byte
order. Resulting from that it can be assessed that the check in
`emcutes`'s `set_len()` function is wrong as it needs to be checked if
`len` is lesser or equal to `0xff - 1`. `len <= (0xff - 1)` can be
simplified to `len < 0xff`. For some larger packages this safes 2 bytes
of wasted packet space.
`len` is used with the `memcpy()` to copy the payload to `tbuf`. With a
payload provided that is just long enough to fill `tbuf`, `len += 6`
leads to the `memcpy()` overriding data after `tbuf` (e.g. the
`mutex` that is unlocked right after) and thus resulting in potential
segmentation faults.
Additionally `+ 6` can only be applied if the total packet length is
below 256 (see spec), so `len + pos` is what needs to be provided to the
corresponding send functions instead (`pos` adapts to the header length
of the PUBLISH message).
A new blue pill variant with only 32 KiB of flash (secretly coming with
64 KiB flash) instead of the use 64 KiB flash (secretly coming with 128 KiB)
is not compatible with `make flash`. This commit changes the OpenOCD config
so that both variants can be flashed.
