zipl/boot: declare that no executable stack is required

Normally, `gcc` takes care of adding the `GNU_STACK` marking except for
assembly code. Therefore, let's add the marking manually. Discard the
`.note.GNU-stack` section in the linker script since it's just a
"message" from the compiler to the linker. This fixes the linker
warning:

ld: warning: entry.o: missing .note.GNU-stack section implies executable stack

Acked-by: Eduard Shishkin <edward6@linux.ibm.com>
Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

zipl/boot/entry.S

@@ -18,3 +18,8 @@ pgm_check_handler:
 	basr	%r14,%r14
 	lmg	%r0,%r15,__LC_SAVE_AREA_SYNC
 	lpswe	__LC_PGM_OLD_PSW(%r0)
+
+/* The code doesn't require an executable stack */
+#if defined(__linux__) && defined(__ELF__)
+.section .note.GNU-stack,"",%progbits
+#endif

zipl/boot/head.S

@@ -28,3 +28,8 @@ _start:
 	brasl	%r14,initialize
 .Lstack: .long  0x10000-160
 .previous
+
+/* The code doesn't require an executable stack */
+#if defined(__linux__) && defined(__ELF__)
+.section .note.GNU-stack,"",%progbits
+#endif

zipl/boot/stage2.lds.S

@@ -94,5 +94,6 @@ SECTIONS
   /DISCARD/ : {
     *(.eh_frame)
     *(.interp)
+    *(.note.GNU-stack)
   }
 }

zipl/boot/stage3.lds.S

@@ -79,5 +79,6 @@ SECTIONS
   /DISCARD/ : {
     *(.eh_frame)
     *(.interp)
+    *(.note.GNU-stack)
   }
 }