Using the libraries in a nonsemihosting environment
Some C library functions use semihosting. If you use the libraries in a nonsemihosting environment, you must ensure that semihosting function calls are dealt with appropriately.
If you do not want to use semihosting, either:
- Remove all calls to semihosting functions.
Re-implement the lower-level functions, for example,
fputc(). You are not required to re-implement all semihosting functions. You must, however, re-implement the functions you are using in your application.
You must re-implement functions that the C library uses to isolate itself from target dependencies. For example, if you use
printf()you must re-implement
fputc(). If you do not use the higher-level input/output functions like
printf(), you do not have to re-implement the lower-level functions like
- Implement a handler for all of the semihosting calls to be handled in your own specific way. One such example is for the handler to intercept the calls, redirecting them to your own nonsemihosted, that is, target-specific, functions.
To guarantee that no functions using semihosting are included in your application, use either:
IMPORT __use_no_semihostingfrom armasm assembly language.
__asm(".global __use_no_semihosting\n\t")for C or C++ code.
IMPORT __use_no_semihostingis only required to be added to a single assembly source file. Similarly,
__asm(".global __use_no_semihosting\n\t")is only required to be added to a single C source file. It is unnecessary to add these inserts to every single source file.
If you include a library function that uses semihosting and also reference __use_no_semihosting, the library detects the conflicting symbols and the linker reports an error. For example, to determine which objects are using semihosting when using an Armv8‑M processor:
- Link with
armlink --cpu=8-M --verbose --list err.txt
Search err.txt for occurrences of
... Loading member sys_exit.o from c_2.l. reference : __I$use$semihosting definition: _sys_exit ...
This shows that the semihosting-using function
_sys_exitis linked-in from the C library. To prevent this, you must provide your own implementation of this function.
There are no target-dependent functions in the C++ library, although some C++ functions use underlying C library functions that are target-dependent.