Clarify comment.

sysdeps/unix/sysv/linux/x86_64/sysdep.h

@@ -134,37 +134,42 @@
   jmp L(pseudo_end);
 #endif	/* PIC */
 
-/* Linux/x86-64 takes system call arguments in registers:
+/* The Linux/x86-64 kernel expects the system call parameters in
+   registers according to the following table:
 
-    Register setup:
-    system call number	rax
+    syscall number	rax
     arg 1		rdi
     arg 2		rsi
     arg 3		rdx
-    arg 4		rcx
+    arg 4		r10
     arg 5		r8
     arg 6		r9
 
+    The Linux kernel uses and destroys internally these registers:
     return address from
     syscall		rcx
     additionally clobered: r12-r15,rbx,rbp
     eflags from syscall	r11
 
-    The compiler is going to form a call by coming here, through PSEUDO, with arguments:
+    Normal function call, including calls to the system call stub
+    functions in the libc, get the first six parameters passed in
+    registers and the seventh parameter and later on the stack.  The
+    register use is as follows:
 
-	syscall number	in the DO_CALL macro
-	arg 1		rdi
-	arg 2		rsi
-	arg 3		rdx
-	arg 4		r10
-	arg 5		r8
-	arg 6		r9
+     system call number	in the DO_CALL macro
+     arg 1		rdi
+     arg 2		rsi
+     arg 3		rdx
+     arg 4		rcx
+     arg 5		r8
+     arg 6		r9
 
-     We have to take care that the stack is alignedto 16 bytes.	 When
-     called the stack is not aligned since the return address has just
-     been pushed.
+    We have to take care that the stack is aligned to 16 bytes.  When
+    called the stack is not aligned since the return address has just
+    been pushed.
 
-     Syscalls of more than 6 arguments are not supported.  */
+     
+    Syscalls of more than 6 arguments are not supported.  */
 
 #undef	DO_CALL
 #define DO_CALL(syscall_name, args)		\