Make struct syscall_args machine independent

After a round of cleanups in late 2020, all definitions are
functionally identical.

This removes a rotted __aligned(8) on arm. It was added in
b7112ead32 and was intended to align the
args member so that 64-bit types (off_t, etc) could be safely read on
armeb compiled with clang. With the removal of armev, this is no
longer needed (armv7 requires that 32-bit aligned reads of 64-bit
values be supported and we enable such support on armv6).  As further
evidence this is unnecessary, cleanups to struct syscall_args have
resulted in args being 32-bit aligned on 32-bit systems.  The sole
effect is to bloat the struct by 4 bytes.

Reviewed by:	kib, jhb, imp
Differential Revision:	https://reviews.freebsd.org/D33308

sys/amd64/include/proc.h

@@ -91,13 +91,6 @@ struct mdproc {
 #define	KINFO_PROC_SIZE 1088
 #define	KINFO_PROC32_SIZE 768
 
-struct syscall_args {
-	u_int code;
-	u_int original_code;
-	struct sysent *callp;
-	register_t args[8];
-};
-
 #ifdef	_KERNEL
 
 /* Get the current kernel thread stack usage. */

sys/arm/include/proc.h

@@ -56,22 +56,6 @@ struct mdproc {
 
 #define	KINFO_PROC_SIZE 816
 
-#define MAXARGS	8
-/*
- * This holds the syscall state for a single system call.
- * As some syscall arguments may be 64-bit aligned we need to ensure the
- * args value is 64-bit aligned. The ABI will then ensure any 64-bit
- * arguments are already correctly aligned, even if they were passed in
- * via registers, we just need to make sure we copy them to an aligned
- * buffer.
- */
-struct syscall_args {
-	u_int code;
-	u_int original_code;
-	struct sysent *callp;
-	register_t args[MAXARGS];
-} __aligned(8);
-
 #ifdef _KERNEL
 #include <machine/pcb.h>
 

sys/arm64/include/proc.h

@@ -47,14 +47,6 @@ struct mdproc {
 #define	KINFO_PROC_SIZE	1088
 #define	KINFO_PROC32_SIZE 816
 
-#define	MAXARGS		8
-struct syscall_args {
-	u_int code;
-	u_int original_code;
-	struct sysent *callp;
-	register_t args[MAXARGS];
-};
-
 #ifdef _KERNEL
 
 #include <machine/pcb.h>

sys/i386/include/proc.h

@@ -62,13 +62,6 @@ struct mdproc {
 
 #define	KINFO_PROC_SIZE 768
 
-struct syscall_args {
-	u_int code;
-	u_int original_code;
-	struct sysent *callp;
-	register_t args[8];
-};
-
 #ifdef	_KERNEL
 
 #include <machine/md_var.h>

sys/mips/include/proc.h

@@ -81,14 +81,6 @@ struct mdproc {
 	size_t		md_tls_tcb_offset;	/* TCB offset */
 };
 
-#define	MAXARGS		8
-struct syscall_args {
-	u_int code;
-	u_int original_code;
-	struct sysent *callp;
-	register_t args[MAXARGS];
-};
-
 #ifdef __mips_n64
 #define	KINFO_PROC_SIZE 1088
 #define	KINFO_PROC32_SIZE 816

sys/powerpc/include/proc.h

@@ -59,14 +59,6 @@ struct mdproc {
 #define	KINFO_PROC_SIZE 816
 #endif
 
-#define	MAXARGS		8
-struct syscall_args {
-	u_int code;
-	u_int original_code;
-	struct sysent *callp;
-	register_t args[MAXARGS];
-};
-
 #ifdef _KERNEL
 
 #include <machine/pcb.h>

sys/riscv/include/proc.h

@@ -45,14 +45,6 @@ struct mdproc {
 
 #define	KINFO_PROC_SIZE	1088
 
-#define	MAXARGS		8
-struct syscall_args {
-	u_int code;
-	u_int original_code;
-	struct sysent *callp;
-	register_t args[MAXARGS];
-};
-
 #ifdef _KERNEL
 #include <machine/pcb.h>
 

sys/sys/proc.h

@@ -193,7 +193,6 @@ struct racct;
 struct sbuf;
 struct sleepqueue;
 struct socket;
-struct syscall_args;
 struct td_sched;
 struct thread;
 struct trapframe;
@@ -202,6 +201,14 @@ struct vm_map;
 struct vm_map_entry;
 struct epoch_tracker;
 
+#define MAXARGS	8
+struct syscall_args {
+	u_int code;
+	u_int original_code;
+	struct sysent *callp;
+	register_t args[MAXARGS];
+};
+
 /*
  * XXX: Does this belong in resource.h or resourcevar.h instead?
  * Resource usage extension.  The times in rusage structs in the kernel are