Question

I am developing a bare metal C applications on an ST ARM-Cortex-M3. I have also developed libraries that are usable across all these applications.

I used to use Keil ARM-MDK, but want to move over to GNU-GCC. I thus downloaded the latest version of GCC and started recompiling the code.

Although similar questions to this one have been answered, it does not solve my problem ans therefore I am posting my question.

I have a problem with the following:
Lib_Flash has a function Read_Flash(). Lib_AppCfg links in Lib_Flash as it uses Read_Flash().
My application (App) links in both Lib_Flash and Lib_AppCfg. App also uses Read_Flash() for some specific FLASH checks.
In Keil MDK-ARM it worked fine.
With GCC, when functions using Lib_AppCfg are built, I get errors stating that Read_Flash() is an “undefined reference”.
I am not sure where the problem lies. Is it in the linking of the Lib_Appcfg is built or is the problem when I link App?

Please advise. If you need additional information, please let me know.

Answer 1

The GNU linker by default searches the libraries once in the order listed on the command line. So if a library later in the list has a reference to symbol defined in an earlier library or object file, then it cannot be resolved.

The simple solution is to use library grouping; this causes the linker to repeatedly search a list of libraries until no further synbols can be resolved. If you are invoking the linker (ld) separately, then the linker options are:

--start-group _Flash _AppCfg --end-group

or the alternative form

-( _Flash _AppCfg -)

See the GNU linker manual for details. If driving the linker indirectly through gcc you pass linker options via the -Wl option, something like:

-Wl,-(,_Flash,_AppCfg,-)

I think.