[RFC PATCH] linker script: unify usage of discard definition

[Tejun Heo <tj@kernel.org>]

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.

On x86-64 which explicitly includes EXIT_TEXT, this produces identical
output as before and all but one archs included directives (include or
discard) for all default discarded sections, so this patch shouldn't
cause any behavior difference.

The only problem case is microblaze, which didn't explicitly included
EXIT_TEXT and DATA but didn't discard them either leaving ld to create
identically names output sections for them.  This patch will make the
end result different by throwing away exit text and data.  It looks
like the ommission was accidental and throwing away is the right thing
to do, but I won't push it till someone who knows microblaze confirms
it.

This patch is on top of the current percpu#for-next.

  git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu.git for-next

Thanks.

NOT_SIGNED_OFF_YET
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: Paul Mundt <lethal@linux-sh.org>
Cc: Tony Luck <tony.luck@intel.com>
---
 arch/alpha/kernel/vmlinux.lds.S      |   10 ++--------
 arch/avr32/kernel/vmlinux.lds.S      |   10 +++-------
 arch/blackfin/kernel/vmlinux.lds.S   |    6 +-----
 arch/cris/kernel/vmlinux.lds.S       |   10 ++--------
 arch/frv/kernel/vmlinux.lds.S        |    2 +-
 arch/h8300/kernel/vmlinux.lds.S      |    6 ++----
 arch/ia64/kernel/vmlinux.lds.S       |   22 +++++++++-------------
 arch/m32r/kernel/vmlinux.lds.S       |   11 +++--------
 arch/m68k/kernel/vmlinux-std.lds     |   11 +++--------
 arch/m68k/kernel/vmlinux-sun3.lds    |   10 ++--------
 arch/m68knommu/kernel/vmlinux.lds.S  |    8 +-------
 arch/microblaze/kernel/vmlinux.lds.S |    2 +-
 arch/mips/kernel/vmlinux.lds.S       |   22 ++++++++++------------
 arch/mn10300/kernel/vmlinux.lds.S    |    9 +++------
 arch/parisc/kernel/vmlinux.lds.S     |    9 ++++-----
 arch/powerpc/kernel/vmlinux.lds.S    |   10 +++-------
 arch/s390/kernel/vmlinux.lds.S       |   10 +++-------
 arch/sh/kernel/vmlinux.lds.S         |   11 ++++-------
 arch/sparc/kernel/vmlinux.lds.S      |    9 ++-------
 arch/um/include/asm/common.lds.S     |    5 -----
 arch/um/kernel/dyn.lds.S             |    2 +-
 arch/um/kernel/uml.lds.S             |    2 +-
 arch/x86/kernel/vmlinux.lds.S        |   11 ++++-------
 arch/xtensa/kernel/vmlinux.lds.S     |   14 ++++----------
 include/asm-generic/vmlinux.lds.h    |   14 ++++++++------
 25 files changed, 77 insertions(+), 159 deletions(-)

Index: work/arch/alpha/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/alpha/kernel/vmlinux.lds.S
+++ work/arch/alpha/kernel/vmlinux.lds.S
@@ -134,14 +134,6 @@ SECTIONS
 	__bss_stop = .;
 	_end = .;
 
-	/* Sections to be discarded */
-	/DISCARD/ : {
-		EXIT_TEXT
-		EXIT_DATA
-		*(.exitcall.exit)
-		*(.discard)
-	}
-
 	.mdebug 0 : {
 		*(.mdebug)
 	}
@@ -151,4 +143,6 @@ SECTIONS
 
 	STABS_DEBUG
 	DWARF_DEBUG
+
+	DISCARDS
 }
Index: work/arch/avr32/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/avr32/kernel/vmlinux.lds.S
+++ work/arch/avr32/kernel/vmlinux.lds.S
@@ -124,15 +124,11 @@ SECTIONS
 		_end = .;
 	}
 
+	DWARF_DEBUG
+
 	/* When something in the kernel is NOT compiled as a module, the module
 	 * cleanup code and data are put into these segments. Both can then be
 	 * thrown away, as cleanup code is never called unless it's a module.
 	 */
-	/DISCARD/       	: {
-		EXIT_DATA
-		*(.exitcall.exit)
-		*(.discard)
-	}
-
-	DWARF_DEBUG
+	DISCARDS
 }
Index: work/arch/blackfin/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/blackfin/kernel/vmlinux.lds.S
+++ work/arch/blackfin/kernel/vmlinux.lds.S
@@ -277,9 +277,5 @@ SECTIONS
 
 	DWARF_DEBUG
 
-	/DISCARD/ :
-	{
-		*(.exitcall.exit)
-		*(.discard)
-	}
+	DISCARDS
 }
Index: work/arch/cris/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/cris/kernel/vmlinux.lds.S
+++ work/arch/cris/kernel/vmlinux.lds.S
@@ -140,13 +140,7 @@ SECTIONS
 	_end = .;
 	__end = .;
 
-	/* Sections to be discarded */
-	/DISCARD/ : {
-		EXIT_TEXT
-		EXIT_DATA
-		*(.exitcall.exit)
-		*(.discard)
-        }
-
 	dram_end = dram_start + (CONFIG_ETRAX_DRAM_SIZE - __CONFIG_ETRAX_VMEM_SIZE)*1024*1024;
+
+	DISCARDS
 }
Index: work/arch/frv/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/frv/kernel/vmlinux.lds.S
+++ work/arch/frv/kernel/vmlinux.lds.S
@@ -178,7 +178,7 @@ SECTIONS
 
   .comment 0 : { *(.comment) }
 
-  /DISCARD/ : { *(.discard) }
+  DISCARDS
 }
 
 __kernel_image_size_no_bss = __bss_start - __kernel_image_start;
Index: work/arch/h8300/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/h8300/kernel/vmlinux.lds.S
+++ work/arch/h8300/kernel/vmlinux.lds.S
@@ -152,10 +152,6 @@ SECTIONS
 	__end = . ;
 	__ramstart = .;
 	}
-	/DISCARD/ : {
-		*(.exitcall.exit)
-		*(.discard)
-	}
         .romfs :	
 	{
 		*(.romfs*)
@@ -166,4 +162,6 @@ SECTIONS
 	COMMAND_START = . - 0x200 ;
 	__ramend = . ;
 	}
+
+	DISCARDS
 }
Index: work/arch/ia64/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/ia64/kernel/vmlinux.lds.S
+++ work/arch/ia64/kernel/vmlinux.lds.S
@@ -24,16 +24,6 @@ PHDRS {
 }
 SECTIONS
 {
-  /* Sections to be discarded */
-  /DISCARD/ : {
-	EXIT_TEXT
-	EXIT_DATA
-	*(.exitcall.exit)
-	*(.discard)
-	*(.IA_64.unwind.exit.text)
-	*(.IA_64.unwind_info.exit.text)
-	}
-
   v = PAGE_OFFSET;	/* this symbol is here to make debugging easier... */
   phys_start = _start - LOAD_OFFSET;
 
@@ -317,7 +307,13 @@ SECTIONS
   .debug_funcnames 0 : { *(.debug_funcnames) }
   .debug_typenames 0 : { *(.debug_typenames) }
   .debug_varnames  0 : { *(.debug_varnames) }
-  /* These must appear regardless of  .  */
-  /DISCARD/ : { *(.comment) }
-  /DISCARD/ : { *(.note) }
+
+  /* Sections to be discarded */
+  DISCARDS
+  /DISCARD/ : {
+	*(.IA_64.unwind.exit.text)
+	*(.IA_64.unwind_info.exit.text)
+	*(.comment)
+	*(.note)
+	}
 }
Index: work/arch/m32r/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/m32r/kernel/vmlinux.lds.S
+++ work/arch/m32r/kernel/vmlinux.lds.S
@@ -120,14 +120,6 @@ SECTIONS
 
   _end = . ;
 
-  /* Sections to be discarded */
-  /DISCARD/ : {
-	EXIT_TEXT
-	EXIT_DATA
-	*(.exitcall.exit)
-	*(.discard)
-	}
-
   /* Stabs debugging sections.  */
   .stab 0 : { *(.stab) }
   .stabstr 0 : { *(.stabstr) }
@@ -136,4 +128,7 @@ SECTIONS
   .stab.index 0 : { *(.stab.index) }
   .stab.indexstr 0 : { *(.stab.indexstr) }
   .comment 0 : { *(.comment) }
+
+  /* Sections to be discarded */
+  DISCARDS
 }
Index: work/arch/m68knommu/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/m68knommu/kernel/vmlinux.lds.S
+++ work/arch/m68knommu/kernel/vmlinux.lds.S
@@ -184,13 +184,6 @@ SECTIONS {
 		__init_end = .;
 	} > INIT
 
-	/DISCARD/ : {
-		EXIT_TEXT
-		EXIT_DATA
-		*(.exitcall.exit)
-		*(.discard)
-	}
-
 	.bss : {
 		. = ALIGN(4);
 		_sbss = . ;
@@ -201,5 +194,6 @@ SECTIONS {
 	 	_end = . ;
 	} > BSS
 
+	DISCARDS
 }
 
Index: work/arch/microblaze/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/microblaze/kernel/vmlinux.lds.S
+++ work/arch/microblaze/kernel/vmlinux.lds.S
@@ -163,5 +163,5 @@ SECTIONS {
 	. = ALIGN(4096);
 	_end = .;
 
-	/DISCARD/ : { *(.discard) }
+	DISCARDS
 }
Index: work/arch/mips/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/mips/kernel/vmlinux.lds.S
+++ work/arch/mips/kernel/vmlinux.lds.S
@@ -176,18 +176,6 @@ SECTIONS
 
 	_end = . ;
 
-	/* Sections to be discarded */
-	/DISCARD/ : {
-		*(.exitcall.exit)
-		*(.discard)
-
-		/* ABI crap starts here */
-		*(.MIPS.options)
-		*(.options)
-		*(.pdr)
-		*(.reginfo)
-	}
-
 	/* These mark the ABI of the kernel for debuggers.  */
 	.mdebug.abi32 : {
 		KEEP(*(.mdebug.abi32))
@@ -213,4 +201,14 @@ SECTIONS
 		*(.gptab.bss)
 		*(.gptab.sbss)
 	}
+
+	/* Sections to be discarded */
+	DISCARDS
+	/DISCARD/ : {
+		/* ABI crap starts here */
+		*(.MIPS.options)
+		*(.options)
+		*(.pdr)
+		*(.reginfo)
+	}
 }
Index: work/arch/mn10300/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/mn10300/kernel/vmlinux.lds.S
+++ work/arch/mn10300/kernel/vmlinux.lds.S
@@ -115,13 +115,10 @@ SECTIONS
   . = ALIGN(PAGE_SIZE);
   pg0 = .;
 
-  /* Sections to be discarded */
-  /DISCARD/ : {
-	EXIT_CALL
-	*(.discard)
-	}
-
   STABS_DEBUG
 
   DWARF_DEBUG
+
+  /* Sections to be discarded */
+  DISCARDS
 }
Index: work/arch/parisc/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/parisc/kernel/vmlinux.lds.S
+++ work/arch/parisc/kernel/vmlinux.lds.S
@@ -237,10 +237,12 @@ SECTIONS
 	/* freed after init ends here */
 	_end = . ;
 
+	STABS_DEBUG
+	.note 0 : { *(.note) }
+
 	/* Sections to be discarded */
+	DISCARDS
 	/DISCARD/ : {
-		*(.exitcall.exit)
-		*(.discard)
 #ifdef CONFIG_64BIT
 		/* temporary hack until binutils is fixed to not emit these
 	 	 * for static binaries
@@ -253,7 +255,4 @@ SECTIONS
 		*(.gnu.hash)
 #endif
 	}
-
-	STABS_DEBUG
-	.note 0 : { *(.note) }	
 }
Index: work/arch/powerpc/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/powerpc/kernel/vmlinux.lds.S
+++ work/arch/powerpc/kernel/vmlinux.lds.S
@@ -37,13 +37,6 @@ jiffies = jiffies_64 + 4;
 #endif
 SECTIONS
 {
-	/* Sections to be discarded. */
-	/DISCARD/ : {
-	*(.exitcall.exit)
-	*(.discard)
-	EXIT_DATA
-	}
-
 	. = KERNELBASE;
 
 /*
@@ -299,4 +292,7 @@ SECTIONS
 	. = ALIGN(PAGE_SIZE);
 	_end = . ;
 	PROVIDE32 (end = .);
+
+	/* Sections to be discarded. */
+	DISCARDS
 }
Index: work/arch/s390/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/s390/kernel/vmlinux.lds.S
+++ work/arch/s390/kernel/vmlinux.lds.S
@@ -157,14 +157,10 @@ SECTIONS
 
 	_end = . ;
 
-	/* Sections to be discarded */
-	/DISCARD/ : {
-		EXIT_DATA
-		*(.exitcall.exit)
-		*(.discard)
-	}
-
 	/* Debugging sections.	*/
 	STABS_DEBUG
 	DWARF_DEBUG
+
+	/* Sections to be discarded */
+	DISCARDS
 }
Index: work/arch/sh/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/sh/kernel/vmlinux.lds.S
+++ work/arch/sh/kernel/vmlinux.lds.S
@@ -163,17 +163,14 @@ SECTIONS
 		_end = . ;
 	}
 
+	STABS_DEBUG
+	DWARF_DEBUG
+
 	/*
 	 * When something in the kernel is NOT compiled as a module, the
 	 * module cleanup code and data are put into these segments. Both
 	 * can then be thrown away, as cleanup code is never called unless
 	 * it's a module.
 	 */
-	/DISCARD/ : {
-		*(.exitcall.exit)
-		*(.discard)
-	}
-
-	STABS_DEBUG
-	DWARF_DEBUG
+	DISCARDS
 }
Index: work/arch/sparc/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/sparc/kernel/vmlinux.lds.S
+++ work/arch/sparc/kernel/vmlinux.lds.S
@@ -171,13 +171,8 @@ SECTIONS
 	}
 	_end = . ;
 
-	/DISCARD/ : {
-		EXIT_TEXT
-		EXIT_DATA
-		*(.exitcall.exit)
-		*(.discard)
-	}
-
 	STABS_DEBUG
 	DWARF_DEBUG
+
+	DISCARDS
 }
Index: work/arch/x86/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/x86/kernel/vmlinux.lds.S
+++ work/arch/x86/kernel/vmlinux.lds.S
@@ -387,15 +387,12 @@ SECTIONS
 		_end = .;
 	}
 
-	/* Sections to be discarded */
-	/DISCARD/ : {
-		*(.exitcall.exit)
-		*(.eh_frame)
-		*(.discard)
-	}
-
         STABS_DEBUG
         DWARF_DEBUG
+
+	/* Sections to be discarded */
+	DISCARDS
+	/DISCARD/ : { *(.eh_frame) }
 }
 
 
Index: work/arch/xtensa/kernel/vmlinux.lds.S
===================================================================
--- work.orig/arch/xtensa/kernel/vmlinux.lds.S
+++ work/arch/xtensa/kernel/vmlinux.lds.S
@@ -280,16 +280,6 @@ SECTIONS
     *(.ResetVector.text)
   }
 
-  /* Sections to be discarded */
-  /DISCARD/ :
-  {
-	*(.exit.literal)
-	EXIT_TEXT
-	EXIT_DATA
-        *(.exitcall.exit)
-	*(.discard)
-  }
-
   .xt.lit : { *(.xt.lit) }
   .xt.prop : { *(.xt.prop) }
 
@@ -322,4 +312,8 @@ SECTIONS
     *(.xt.lit)
     *(.gnu.linkonce.p*)
   }
+
+  /* Sections to be discarded */
+  DISCARDS
+  /DISCARD/ : { *(.exit.literal) }
 }
Index: work/include/asm-generic/vmlinux.lds.h
===================================================================
--- work.orig/include/asm-generic/vmlinux.lds.h
+++ work/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 +626,16 @@
 #define INIT_RAM_FS
 #endif
 
+/*
+ * DISCARDS must be the last and archs which want some of the default
+ * discarded sections in the kernel image can do so by putting them in
+ * earlier section definition.
+ */
 #define DISCARDS							\
 	/DISCARD/ : {							\
 	EXIT_TEXT							\
 	EXIT_DATA							\
-	*(.exitcall.exit)						\
+	EXIT_CALL							\
 	*(.discard)							\
 	}
 
Index: work/arch/m68k/kernel/vmlinux-std.lds
===================================================================
--- work.orig/arch/m68k/kernel/vmlinux-std.lds
+++ work/arch/m68k/kernel/vmlinux-std.lds
@@ -82,14 +82,6 @@ SECTIONS
 
   _end = . ;
 
-  /* Sections to be discarded */
-  /DISCARD/ : {
-	EXIT_TEXT
-	EXIT_DATA
-	*(.exitcall.exit)
-	*(.discard)
-	}
-
   /* Stabs debugging sections.  */
   .stab 0 : { *(.stab) }
   .stabstr 0 : { *(.stabstr) }
@@ -98,4 +90,7 @@ SECTIONS
   .stab.index 0 : { *(.stab.index) }
   .stab.indexstr 0 : { *(.stab.indexstr) }
   .comment 0 : { *(.comment) }
+
+  /* Sections to be discarded */
+  DISCARDS
 }
Index: work/arch/m68k/kernel/vmlinux-sun3.lds
===================================================================
--- work.orig/arch/m68k/kernel/vmlinux-sun3.lds
+++ work/arch/m68k/kernel/vmlinux-sun3.lds
@@ -77,14 +77,6 @@ __init_begin = .;
 
   _end = . ;
 
-  /* Sections to be discarded */
-  /DISCARD/ : {
-	EXIT_TEXT
-	EXIT_DATA
-	*(.exitcall.exit)
-	*(.discard)
-	}
-
   .crap : {
 	/* Stabs debugging sections.  */
 	*(.stab)
@@ -97,4 +89,6 @@ __init_begin = .;
 	*(.note)
   }
 
+  /* Sections to be discarded */
+  DISCARDS
 }
Index: work/arch/um/include/asm/common.lds.S
===================================================================
--- work.orig/arch/um/include/asm/common.lds.S
+++ work/arch/um/include/asm/common.lds.S
@@ -123,8 +123,3 @@
 	__initramfs_end = .;
   }
 
-  /* Sections to be discarded */
-  /DISCARD/ : {
- 	*(.exitcall.exit)
-  }
-
Index: work/arch/um/kernel/dyn.lds.S
===================================================================
--- work.orig/arch/um/kernel/dyn.lds.S
+++ work/arch/um/kernel/dyn.lds.S
@@ -157,5 +157,5 @@ SECTIONS
 
   DWARF_DEBUG
 
-  /DISCARD/	: { *(.discard) }
+  DISCARDS
 }
Index: work/arch/um/kernel/uml.lds.S
===================================================================
--- work.orig/arch/um/kernel/uml.lds.S
+++ work/arch/um/kernel/uml.lds.S
@@ -101,5 +101,5 @@ SECTIONS
 
   DWARF_DEBUG
 
-  /DISCARD/	: { *(.discard) }
+  DISCARDS
 }