core: do not trace syscall_log()

Tracing the log syscall is of very little value since it will generate
some output to the console anyways. Worse, it pollutes the TA output in
case of a panic or an abort. For example:

 o regression_4005.1 AE case 0 algo 0x40000710 line 2819
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#27 (syscall_cryp_obj_alloc)
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#15 (syscall_cryp_state_alloc)
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#27 (syscall_cryp_obj_alloc)
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#24 (syscall_cryp_obj_get_info)
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#30 (syscall_cryp_obj_populate)
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#24 (syscall_cryp_obj_get_info)
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#24 (syscall_cryp_obj_get_info)
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#29 (syscall_cryp_obj_reset)
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#24 (syscall_cryp_obj_get_info)
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#24 (syscall_cryp_obj_get_info)
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#31 (syscall_cryp_obj_copy)
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#24 (syscall_cryp_obj_get_info)
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#28 (syscall_cryp_obj_close)
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#34 (syscall_authenc_init)
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#2 (syscall_panic)
 E/TC:?? 0
 E/TC:?? 0 TA panicked with code 0xffff0006
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#1 (syscall_log)
 E/LD:  Status of TA cb3e5ba0-adf1-11e0-998b-0002a5d5c51b
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#1 (syscall_log)
 E/LD:   arch: aarch64
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#1 (syscall_log)
 E/LD:  region  0: va 0x40004000 pa 0x100062d000 size 0x002000 flags rw-s (ldelf)
 F/TC:?? 0 trace_syscall:132 syscall OP-TEE#1 (syscall_log)
 E/LD:  region  1: va 0x40006000 pa 0x100062f000 size 0x00d000 flags r-xs (ldelf)
 ...

Therefore, skip the trace if the syscall number it TEE_SCN_LOG.

Signed-off-by: Jerome Forissier <jerome@forissier.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>

Author: jforissier

core/arch/arm/tee/arch_svc.c

@@ -123,7 +123,7 @@ static const struct syscall_entry tee_svc_syscall_table[] = {
 #ifdef TRACE_SYSCALLS
 static void trace_syscall(size_t num)
 {
-	if (num == TEE_SCN_RETURN || num > TEE_SCN_MAX)
+	if (num == TEE_SCN_RETURN || num == TEE_SCN_LOG || num > TEE_SCN_MAX)
 		return;
 	FMSG("syscall #%zu (%s)", num, tee_svc_syscall_table[num].name);
 }