Rework __linux_syscall

The way variadic functions are handled on macOS differs between x86/x86-64 and ARM64.

See the following for more details: https://developer.apple.com/documentation/apple-silicon/addressing-architectural-differences-in-your-macos-code#Dont-Redeclare-a-Function-to-Have-Variable-Parameters

darling/src/libsystem_kernel/emulation/linux/base.c

@@ -18,11 +18,47 @@ long __unknown_syscall_machdep(int nr, ...)
 }
 
 VISIBLE
-int __linux_syscall(int nr, long a1, long a2, long a3, long a4, long a5, long a6)
+int __linux_syscall_6args(int nr, long a1, long a2, long a3, long a4, long a5, long a6)
 {
 	return linux_syscall(a1, a2, a3, a4, a5, a6, nr);
 }
 
+VISIBLE
+int __linux_syscall_noargs(int nr)
+{
+	return __linux_syscall_6args(nr, 0, 0, 0, 0, 0, 0);
+}
+
+VISIBLE
+int __linux_syscall_1arg(int nr, long a1)
+{
+	return __linux_syscall_6args(nr, a1, 0, 0, 0, 0, 0);
+}
+
+VISIBLE
+int __linux_syscall_2args(int nr, long a1, long a2)
+{
+	return __linux_syscall_6args(nr, a1, a2, 0, 0, 0, 0);
+}
+
+VISIBLE
+int __linux_syscall_3args(int nr, long a1, long a2, long a3)
+{
+	return __linux_syscall_6args(nr, a1, a2, a3, 0, 0, 0);
+}
+
+VISIBLE
+int __linux_syscall_4args(int nr, long a1, long a2, long a3, long a4)
+{
+	return __linux_syscall_6args(nr, a1, a2, a3, a4, 0, 0);
+}
+
+VISIBLE
+int __linux_syscall_5args(int nr, long a1, long a2, long a3, long a4, long a5)
+{
+	return __linux_syscall_6args(nr, a1, a2, a3, a4, a5, 0);
+}
+
 #ifdef __TESTING
 void _start()
 {

darling/src/libsystem_kernel/emulation/linux/base.h

@@ -21,8 +21,13 @@ long linux_syscall(long a1, long a2, long a3, long a4, long a5, long a6, int nr)
 
 #ifndef BUILDING_BASE_C
 
-VISIBLE
-int __linux_syscall(int nr, ...);
+VISIBLE int __linux_syscall_noargs(int);
+VISIBLE int __linux_syscall_1arg(int,long);
+VISIBLE int __linux_syscall_2args(int,long,long);
+VISIBLE int __linux_syscall_3args(int,long,long,long);
+VISIBLE int __linux_syscall_4args(int,long,long,long,long);
+VISIBLE int __linux_syscall_5args(int,long,long,long,long,long);
+VISIBLE int __linux_syscall_6args(int,long,long,long,long,long,long);
 
 #endif /* BUILDING_BASE_C */
 

libsyscall/os/tsd.h

@@ -54,6 +54,7 @@
 
 #ifdef DARLING
 #include <darling/emulation/linux-syscalls.h>
+#include <darling/emulation/base.h>
 #endif
 
 extern void _thread_set_tsd_base(void *tsd_base);
@@ -63,10 +64,8 @@ static __inline__ unsigned int
 _os_cpu_number(void)
 {
 #ifdef DARLING
-	extern int __linux_syscall(int nr, ...);
-
 	unsigned int cpu_num = 0;
-	int status = __linux_syscall(__NR_getcpu, &cpu_num, 0, 0, 0, 0, 0);
+	int status = __linux_syscall_3args(__NR_getcpu, (long)&cpu_num, 0, 0);
 	// should we even check? i don't think it's possible for it to fail with these arguments
 	if (status < 0) {
 		return 0; // i guess?