kernel: allow up to 6 arguments for system calls

A quick look at "man syscall" shows that in Linux, all architectures
support at least 6 argument system calls, with a few supporting 7. We
can at least do 6 in Zephyr.

x86 port modified to use EBP register to carry the 6th system call
argument.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>

arch/x86/core/userspace.S

@@ -35,6 +35,7 @@ _id_ok:
 	 * for _k_syscall_handler_t functions
 	 */
 	push	%esp		/* ssf */
+	push	%ebp		/* arg6 */
 	push	%edi		/* arg5 */
 	push	%ebx		/* arg4 */
 #ifndef CONFIG_X86_IAMCU
@@ -63,11 +64,11 @@ _id_ok:
 	pop	%ebx
 	pop	%edi
 #ifndef CONFIG_X86_IAMCU
-	/* Discard ssf, no free register to pop it into so we add instead  */
+	/* Discard ssf and arg6 */
-	add	$4, %esp
+	add	$8, %esp
 #else
-	xor	%edx, %edx	/* Clean EDX */
+	pop	%ecx		/* Clean ECX and get arg6 off the stack */
-	pop	%ecx		/* Clean ECX and get ssf arg off the stack */
+	pop	%edx		/* Clean EDX and get ssf off the stack */
 #endif
 	iret
 

include/arch/x86/arch.h

@@ -560,6 +560,26 @@ extern struct task_state_segment _main_tss;
  * the entry stub clobbers EDX and ECX on IAMCU systems
  */
 
+static inline u32_t _arch_syscall_invoke6(u32_t arg1, u32_t arg2, u32_t arg3,
+					  u32_t arg4, u32_t arg5, u32_t arg6,
+					  u32_t call_id)
+{
+	u32_t ret;
+
+	__asm__ volatile("push %%ebp\n\t"
+			 "mov %[arg6], %%ebp\n\t"
+			 "int $0x80\n\t"
+			 "pop %%ebp\n\t"
+			 : "=a" (ret)
+#ifdef CONFIG_X86_IAMCU
+			   , "=d" (arg2), "=c" (arg3)
+#endif
+			 : "S" (call_id), "a" (arg1), "d" (arg2),
+			   "c" (arg3), "b" (arg4), "D" (arg5),
+			   [arg6] "r" (arg6));
+	return ret;
+}
+
 static inline u32_t _arch_syscall_invoke5(u32_t arg1, u32_t arg2, u32_t arg3,
 					  u32_t arg4, u32_t arg5, u32_t call_id)
 {

include/kernel.h

@@ -3917,6 +3917,10 @@ static inline int _is_user_context(void)
 }
 
 /* Interfaces for invoking system calls */
+static inline u32_t _arch_syscall_invoke6(u32_t arg1, u32_t arg2, u32_t arg3,
+					  u32_t arg4, u32_t arg5, u32_t arg6,
+					  u32_t call_id);
+
 static inline u32_t _arch_syscall_invoke5(u32_t arg1, u32_t arg2, u32_t arg3,
 					  u32_t arg4, u32_t arg5,
 					  u32_t call_id);

include/syscall.h

@@ -31,8 +31,8 @@
  * - Many kernel calls do no sanity checking of parameters other than
  *   assertions. The handler must check all of these conditions using
  *   _SYSCALL_ASSERT()
- * - If the system call has more then 5 arguments, then arg5 will be a pointer
+ * - If the system call has more than 6 arguments, then arg6 will be a pointer
- *   to some struct containing arguments 5+. The struct itself needs to be
+ *   to some struct containing arguments 6+. The struct itself needs to be
  *   validated like any other buffer passed in from userspace, and its members
  *   individually validated (if necessary) and then passed to the real
  *   implementation like normal arguments
@@ -47,6 +47,7 @@
  * @param arg3 system call argument 3
  * @param arg4 system call argument 4
  * @param arg5 system call argument 5
+ * @param arg6 system call argument 6
  * @param ssf System call stack frame pointer. Used to generate kernel oops
  *            via _arch_syscall_oops_at(). Contents are arch-specific.
  * @return system call return value, or 0 if the system call implementation
@@ -54,7 +55,8 @@
  *
  */
 typedef u32_t (*_k_syscall_handler_t)(u32_t arg1, u32_t arg2, u32_t arg3,
-				      u32_t arg4, u32_t arg5, void *ssf);
+				      u32_t arg4, u32_t arg5, u32_t arg6,
+				      void *ssf);
 
 
 extern const _k_syscall_handler_t _k_syscall_table[K_SYSCALL_LIMIT];
@@ -94,18 +96,20 @@ extern const _k_syscall_handler_t _k_syscall_table[K_SYSCALL_LIMIT];
 
 /* Convenience macros for handler implementations */
 #define _SYSCALL_ARG0	ARG_UNUSED(arg1); ARG_UNUSED(arg2); ARG_UNUSED(arg3); \
-			ARG_UNUSED(arg4); ARH_UNUSED(arg5)
+			ARG_UNUSED(arg4); ARH_UNUSED(arg5); ARG_UNUSED(arg6)
 
 #define _SYSCALL_ARG1	ARG_UNUSED(arg2); ARG_UNUSED(arg3); ARG_UNUSED(arg4); \
-			ARG_UNUSED(arg5)
+			ARG_UNUSED(arg5); ARG_UNUSED(arg6)
 
-#define _SYSCALL_ARG2	ARG_UNUSED(arg3); ARG_UNUSED(arg4); ARG_UNUSED(arg5)
+#define _SYSCALL_ARG2	ARG_UNUSED(arg3); ARG_UNUSED(arg4); ARG_UNUSED(arg5); \
+			ARG_UNUSED(arg6)
 
-#define _SYSCALL_ARG3	ARG_UNUSED(arg4); ARG_UNUSED(arg5)
+#define _SYSCALL_ARG3	ARG_UNUSED(arg4); ARG_UNUSED(arg5); ARG_UNUSED(arg6)
-
-#define _SYSCALL_ARG4	ARG_UNUSED(arg5)
 
 
+#define _SYSCALL_ARG4	ARG_UNUSED(arg5); ARG_UNUSED(arg6)
+
+#define _SYSCALL_ARG5	ARG_UNUSED(arg6)
 #endif /* _ASMLANGUAGE */
 
 #endif /* _ZEPHYR_SYSCALL_H_ */

kernel/userspace.c

@@ -183,7 +183,7 @@ void _k_object_init(void *object)
 }
 
 static u32_t _syscall_bad_handler(u32_t bad_id, u32_t arg2, u32_t arg3,
-				  u32_t arg4, u32_t arg5, void *ssf)
+				  u32_t arg4, u32_t arg5, u32_t arg6, void *ssf)
 {
 	printk("Bad system call id %u invoked\n", bad_id);
 	_arch_syscall_oops(ssf);