genprotimg/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

Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

genprotimg/boot/head.S

@@ -29,3 +29,8 @@ _start:
 	brasl	%r14, initialize
 .Lstack: .long STACK_ADDRESS + STACK_SIZE - STACK_FRAME_OVERHEAD
 .previous
+
+/* The code doesn't require an executable stack */
+#if defined(__linux__) && defined(__ELF__)
+.section .note.GNU-stack,"",%progbits
+#endif

genprotimg/boot/stage3a.lds.S

@@ -99,5 +99,6 @@ SECTIONS
 	/* Sections to be discarded */
 	/DISCARD/ : {
 		*(.eh_frame)
+		*(.note.GNU-stack)
 	}
 }

genprotimg/boot/stage3a_init.S

@@ -26,3 +26,8 @@ _init:
 	br	%r1
 .Lstage3a_entry: .long STAGE3A_ENTRY
 .previous
+
+/* The code doesn't require an executable stack */
+#if defined(__linux__) && defined(__ELF__)
+.section .note.GNU-stack,"",%progbits
+#endif

genprotimg/boot/stage3b.lds.S

@@ -83,5 +83,6 @@ SECTIONS
 	/* Sections to be discarded */
 	/DISCARD/ : {
 		*(.eh_frame)
+		*(.note.GNU-stack)
 	}
 }

genprotimg/boot/stage3b_reloc.S

@@ -53,3 +53,8 @@ stage3b_start:
 	.incbin	"stage3b.bin"
 stage3b_end:
 .previous
+
+/* The code doesn't require an executable stack */
+#if defined(__linux__) && defined(__ELF__)
+.section .note.GNU-stack,"",%progbits
+#endif