From a0abb093ed595177a67a21f95c640dcfd7bc4e4c Mon Sep 17 00:00:00 2001
From: Norman Feske <norman.feske@genode-labs.com>
Date: Fri, 16 Jan 2015 09:59:59 +0100
Subject: [PATCH] Remove output-section fill from linker scripts

The linker scripts use to fill alignment gaps within the text section
with the magic value 0x90909090, which correponds to the opcodes of four
nop instructions on x86. This patch removes this value because it
apparently solves no problem. If, for some reason (e.g., due to a dangling
pointer) a thread executes instructions within alignment paddings, NOP
instructions are not any better than any other instruction. The program
will eventually execute the instructions after the padding, which is
most likely fatal. It would be more reasonable to fill the padding with
the opcode of an illegal instruction so that such an error can be
immediately detected. That said, I cannot remember a single instance,
where the fill value has helped us during debugging.

Even if the mechanism served a purpose on x86, it is still better to
remove it because it does not equally work on the other architectures
where the linker scripts are used. I.e., on ARM, the opcode 0x90909090
is not a NOP instruction.
---
 repos/base-codezero/src/platform/genode.ld           | 2 +-
 repos/base-nova/src/platform/roottask.ld             | 2 +-
 repos/base-okl4/src/test/okl4_01_hello_raw/genode.ld | 2 +-
 repos/base/src/platform/genode.ld                    | 2 +-
 repos/base/src/platform/genode_dyn.ld                | 6 +++---
 repos/base/src/platform/genode_rel.ld                | 6 +++---
 6 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/repos/base-codezero/src/platform/genode.ld b/repos/base-codezero/src/platform/genode.ld
index 9a946a5b6..ac7a29f57 100644
--- a/repos/base-codezero/src/platform/genode.ld
+++ b/repos/base-codezero/src/platform/genode.ld
@@ -58,7 +58,7 @@ SECTIONS
 		KEEP (*(SORT(.dtors.*)))
 		KEEP (*(.dtors))
 		_dtors_end = .;
-	} : ro = 0x90909090
+	} : ro = 0x0
 
 	/* Linux: exception section for uaccess mechanism */
 	__ex_table : { *(__ex_table) }
diff --git a/repos/base-nova/src/platform/roottask.ld b/repos/base-nova/src/platform/roottask.ld
index 8b2894c62..d8e118543 100644
--- a/repos/base-nova/src/platform/roottask.ld
+++ b/repos/base-nova/src/platform/roottask.ld
@@ -49,7 +49,7 @@ SECTIONS
 		KEEP (*(SORT(.dtors.*)))
 		KEEP (*(.dtors))
 		_dtors_end = .;
-	} : ro = 0x90909090
+	} : ro = 0x0
 
 	/* Linux: exception section for uaccess mechanism */
 	__ex_table : { *(__ex_table) }
diff --git a/repos/base-okl4/src/test/okl4_01_hello_raw/genode.ld b/repos/base-okl4/src/test/okl4_01_hello_raw/genode.ld
index dc8593517..fbd6f1373 100644
--- a/repos/base-okl4/src/test/okl4_01_hello_raw/genode.ld
+++ b/repos/base-okl4/src/test/okl4_01_hello_raw/genode.ld
@@ -40,7 +40,7 @@ SECTIONS
 		KEEP (*(SORT(.dtors.*)))
 		KEEP (*(.dtors))
 		_dtors_end = .;
-	} : ro = 0x90909090
+	} : ro = 0x0
 
 	/* Linux: exception section for uaccess mechanism */
 	__ex_table : { *(__ex_table) }
diff --git a/repos/base/src/platform/genode.ld b/repos/base/src/platform/genode.ld
index b2a5289d1..d5cab593c 100644
--- a/repos/base/src/platform/genode.ld
+++ b/repos/base/src/platform/genode.ld
@@ -44,7 +44,7 @@ SECTIONS
 		KEEP (*(SORT(.dtors.*)))
 		KEEP (*(.dtors))
 		_dtors_end = .;
-	} : ro = 0x90909090
+	} : ro = 0x0
 
 	/* Linux: exception section for uaccess mechanism */
 	__ex_table : { *(__ex_table) }
diff --git a/repos/base/src/platform/genode_dyn.ld b/repos/base/src/platform/genode_dyn.ld
index 7402b301e..825412846 100644
--- a/repos/base/src/platform/genode_dyn.ld
+++ b/repos/base/src/platform/genode_dyn.ld
@@ -37,7 +37,7 @@ SECTIONS
     *(.text .stub .text.* .gnu.linkonce.t.*)
     /* .gnu.warning sections are handled specially by elf32.em.  */
     *(.gnu.warning)
-  } : ro =0x90909090
+  } : ro =0x0
   
   .interp         : { *(.interp) } : interp : ro
   .note.gnu.build-id : { *(.note.gnu.build-id) }
@@ -77,13 +77,13 @@ SECTIONS
   .init           :
   {
     KEEP (*(.init))
-  } =0x90909090
+  } = 0x0
   .plt            : { *(.plt) }
 
   .fini           :
   {
     KEEP (*(.fini))
-  } =0x90909090
+  } = 0x0
   PROVIDE (__etext = .);
   PROVIDE (_etext = .);
   PROVIDE (etext = .);
diff --git a/repos/base/src/platform/genode_rel.ld b/repos/base/src/platform/genode_rel.ld
index 7400a3776..d6891f760 100644
--- a/repos/base/src/platform/genode_rel.ld
+++ b/repos/base/src/platform/genode_rel.ld
@@ -66,18 +66,18 @@ SECTIONS
   .init           :
   {
     KEEP (*(.init))
-  } =0x90909090
+  } = 0x0
   .plt            : { *(.plt) }
   .text           :
   {
     *(.text .stub .text.* .gnu.linkonce.t.*)
     /* .gnu.warning sections are handled specially by elf32.em.  */
     *(.gnu.warning)
-  } =0x90909090
+  } = 0x0
   .fini           :
   {
     KEEP (*(.fini))
-  } =0x90909090
+  } =0x0
   PROVIDE (__etext = .);
   PROVIDE (_etext = .);
   PROVIDE (etext = .);