core: define syscall_t as void (*)(void)

syscall_t is currently typedef'ed as TEE_Result (*)(void). It is used to
represent a pointer to any system call, in the syscall table for instance.
As such, the exact type behind syscall_t cannot reflect all the syscalls
since they have different prototypes. The current declaration with a
TEE_Result return type was probably chosen because it was a common
characteristic of all syscalls to return a TEE_Result.

However, this type causes compilation warnings with GCC 8.1:

core/arch/arm/tee/arch_svc.c:43:36: warning: cast between incompatible function types from ‘void (*)(long unsigned int)’ to ‘TEE_Result (*)(void)’ {aka ‘unsigned int (*)(void)’} [-Wcast-function-type]
 #define SYSCALL_ENTRY(_fn) { .fn = (syscall_t)_fn }
                                    ^
core/arch/arm/tee/arch_svc.c:50:2: note: in expansion of macro ‘SYSCALL_ENTRY’
  SYSCALL_ENTRY(syscall_sys_return),
  ^~~~~~~~~~~~~

The solution is to use 'void (*)(void)' instead, as explained in the GCC
documentation:

 -Wcast-function-type

  Warn when a function pointer is cast to an incompatible function
  pointer. [...] The function type void (*) (void) is special and matches
  everything, which can be used to suppress this warning. [...]

Link: [1] https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>

0 files changed, 0 insertions, 0 deletions