critical: string formatting bug leading to invalid ulog files

[bkueng]

On master the following code:

        char b[50];
        size_t s = 5;
        snprintf(b, sizeof(b), "char[%zu] %s", s, "test");
        printf("b=%s\n", b);
        printf("char[%zu] %s\n", s, "test");
        snprintf(b, sizeof(b), "%zu", s);
        printf("b=%s\n", b);
        printf("%zu\n", s);

produces:

b=char[%zu] test
char[%zu] test
b=%zu
%zu

on NuttX. The expected output is:

b=char[5] test
char[5] test
b=5
5

As a result all (!) log files are invalid. The reason why it still works is that pyulog does not look at that field for string lengths, but FlightPlot for instance won't open the log.

%zu is both a valid C99 and C11 format specifier. It is used in the logger and at a few other places.

The commit that breaks it is the NuttX upgrade (dc10a68).

@davids5 can you have a look?

[davids5]

@bkueng - The change was introduced in the new stdio/lib_libvsprintf.c. The legacy_libvsprintf is still available but uses more space. Let me see if I can upstream a fix and backport it.

[davids5]

@bkueng - PR submitted upstream - I will back port if it goes in or added at as a reject if not.

[davids5]

Fixed in PX4/NuttX#56