linker script: unify usage of discard definition

Discarded sections in different archs share some commonality but have
considerable differences.  This led to linker script for each arch
implementing its own /DISCARD/ definition, which makes maintaining
tedious and adding new entries error-prone.

This patch makes all linker scripts to move discard definitions to the
end of the linker script and use the common DISCARDS macro.  As ld
uses the first matching section definition, archs can include default
discarded sections by including them earlier in the linker script.

ia64 is notable because it first throws away some ia64 specific
subsections and then include the rest of the sections into the final
image, so those sections must be discarded before the inclusion.

defconfig compile tested for x86, x86-64, powerpc, powerpc64, ia64,
alpha, sparc, sparc64 and s390.  Michal Simek tested microblaze.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Acked-by: Mike Frysinger <vapier@gentoo.org>
Tested-by: Michal Simek <monstr@monstr.eu>
Cc: linux-arch@vger.kernel.org
Cc: Michal Simek <monstr@monstr.eu>
Cc: microblaze-uclinux@itee.uq.edu.au
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Tony Luck <tony.luck@intel.com>

1 files changed, 12 insertions, 6 deletions

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index c5c18ac878ab..ab8ea9b7741e 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -35,13 +35,10 @@
  *      __bss_stop = .;
  *      _end = .;
  *
- *      /DISCARD/ : {
- *              EXIT_TEXT
- *              EXIT_DATA
- *              EXIT_CALL
- *      }
  *      STABS_DEBUG
  *      DWARF_DEBUG
+ *
+ *      DISCARDS                // must be the last
  * }
  *
  * [__init_begin, __init_end] is the init section that may be freed after init
@@ -629,11 +626,20 @@
 #define INIT_RAM_FS
 #endif
 
+/*
+ * Default discarded sections.
+ *
+ * Some archs want to discard exit text/data at runtime rather than
+ * link time due to cross-section references such as alt instructions,
+ * bug table, eh_frame, etc.  DISCARDS must be the last of output
+ * section definitions so that such archs put those in earlier section
+ * definitions.
+ */
 #define DISCARDS                                                        \
         /DISCARD/ : {                                                   \
         EXIT_TEXT                                                       \
         EXIT_DATA                                                       \
-        *(.exitcall.exit)                                               \
+        EXIT_CALL                                                       \
         *(.discard)                                                     \
         }