flex/bison for embedded bare-metal system

I develop software for Cortex M, and for that I use Arm GNU Toolchain.
I need to parse data packages for which I have the grammar.

I have problems with flex though, since it normally requires the libfl.a library which I don't have compiled for cortex M.

How can I get around this problem (other than recompiling just the libfl.a for cortex M)? Maybe some flex parameters?

Also, this raises other doubts for me, since my system is bare-metal:

• I don't have standard I/O functions, I have a custom function that I call qprintf().
• I have no dynamic memory management. I can use FreeRTOS and have, thus, pvPortMalloc() instead of the standard malloc().

so I wonder if, even overcoming the libfl.a problem, flex and bison would have problems with the constraints mentioned above.

libfl.a only defines main and yywrap. So if you don't need either of those (because you have you own main and you either use %option noyywrap or you have your own yywrap), you don't need libfl.a

However, scanners generated by flex do need malloc/realloc from the C library, so if you don't have that, you'll need to supply a replacement. The default YY_INPUT/ECHO macros also use stdio, so you'll need to redefine (or not use) them if you want to avoid that part of the standard library.