libc: Access _logname_valid more efficiently.

The variable _logname_valid is not exported via the version script;
therefore, change C and i386/amd64 assembler code to remove indirection
(which allowed interposition). This makes the code slightly smaller and
faster.

Also, remove #define PIC_GOT from i386/amd64 in !PIC mode. Without PIC,
there is no place containing the address of each variable, so there is no
possible definition for PIC_GOT.

lib/libc/amd64/sys/setlogin.S

@@ -48,12 +48,7 @@ ENTRY(__sys_setlogin)
 	mov	$SYS_setlogin,%rax
 	KERNCALL
 	jb	HIDENAME(cerror)
-#ifdef PIC
-	movq	PIC_GOT(CNAME(_logname_valid)),%rdx
-	movl	$0,(%rdx)
-#else
 	movl	$0,CNAME(_logname_valid)(%rip)
-#endif
 	ret				/* setlogin(name) */
 END(__sys_setlogin)
 

lib/libc/gen/getlogin.c

@@ -50,7 +50,7 @@ __FBSDID("$FreeBSD$");
 
 extern int		_getlogin(char *, int);
 
-int			_logname_valid;		/* known to setlogin() */
+int			_logname_valid __hidden; /* known to setlogin() */
 static pthread_mutex_t	logname_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 static char *

lib/libc/i386/sys/setlogin.S

@@ -41,16 +41,9 @@ __FBSDID("$FreeBSD$");
 .globl	CNAME(_logname_valid)		/* in _getlogin() */
 
 SYSCALL(setlogin)
-#ifdef PIC
 	PIC_PROLOGUE
-	pushl	%eax
-	movl	PIC_GOT(CNAME(_logname_valid)),%eax
-	movl	$0,(%eax)
-	popl	%eax
+	movl	$0,PIC_GOTOFF(CNAME(_logname_valid))
 	PIC_EPILOGUE
-#else
-	movl	$0,CNAME(_logname_valid)
-#endif
 	ret				/* setlogin(name) */
 END(__sys_setlogin)
 

sys/amd64/include/asm.h

@@ -43,7 +43,6 @@
 #define	PIC_GOT(x)	x@GOTPCREL(%rip)
 #else
 #define	PIC_PLT(x)	x
-#define	PIC_GOT(x)	x
 #endif
 
 /*

sys/i386/include/asm.h

@@ -49,11 +49,12 @@
 	popl	%ebx
 #define	PIC_PLT(x)	x@PLT
 #define	PIC_GOT(x)	x@GOT(%ebx)
+#define	PIC_GOTOFF(x)	x@GOTOFF(%ebx)
 #else
 #define	PIC_PROLOGUE
 #define	PIC_EPILOGUE
 #define	PIC_PLT(x)	x
-#define	PIC_GOT(x)	x
+#define	PIC_GOTOFF(x)	x
 #endif
 
 /*