RE: SVCALL warning messages

Austin — Thu, 19 Oct 2017 11:45:54 GMT

This error occurs with GCC when -Wunused-parameter is enabled (either directly or both other options such as -Wextra). It seems that using GCC pragmas to turn off unused parameter warnings does not work; the GCC 'unused' attribute must be attached directly to the unused parameter.

A tedious workaround for this problem is to modify nrf_svc.h as follows by adding SVC_PARAM macro:

#ifdef SVCALL_AS_NORMAL_FUNCTION
#define SVCALL(number, return_type, signature) return_type signature
#define SVC_PARAM(x)  x
#else


#if defined (__GNUC__)
#define SVC_PARAM(x)  SVC_PARAM_ ## x __attribute__((__unused__))
#else
#define SVC_PARAM(x)  x
#endif    
...

In each of the instances where the SVCALL() macro is used, modify each call as follows, replacing the parameter name X with SVC_PARAM(X). This will apply the unused GCC attribute directly to the parameter when the SoftDevice is compiled using SVC instructions.

Before:

SVCALL(SD_RAND_APPLICATION_VECTOR_GET, uint32_t, sd_rand_application_vector_get(uint8_t * p_buff, uint8_t length));

After:

 SVCALL(SD_MUTEX_NEW, uint32_t, sd_mutex_new(nrf_mutex_t * SVC_PARAM(p_mutex)));
SVCALL(SD_RAND_APPLICATION_VECTOR_GET, uint32_t, sd_rand_application_vector_get(uint8_t * SVC_PARAM(p_buff), uint8_t SVC_PARAM(length)));

@nordicdevs Is there any chance that a change to the SoftDevice source could be made to accommodate removal of unused parameter warnings on GCC?

RE: SVCALL warning messages

kane — Fri, 20 May 2016 19:03:27 GMT

This change should stop the warnings from coming up.
Credit to this answer.
Cast number as uint16_t, and ignore -Wunused-parameter
Note: it doesn't actually fix the unused parameter warnings just masks them

#define SVCALL(number, return_type, signature) \
  _Pragma("GCC diagnostic ignored \"-Wunused-function\"") \
  _Pragma("GCC diagnostic ignored \"-Wunused-parameter\"") \
  _Pragma("GCC diagnostic push") \
  _Pragma("GCC diagnostic ignored \"-Wreturn-type\"") \
  __attribute__((naked)) static return_type signature \
  { \
    __asm( \
        "svc %0\n" \
        "bx r14" : : "I" ((uint16_t)number) : "r0" \
    ); \
  }    \
  _Pragma("GCC diagnostic pop")