Re: ELF ld script optimisation

[Bob Wilson <bwilson at tensilica dot com>]

Alan Modra wrote:
> I've been playing with ideas for SPU dynamic libraries.  One oddity is
> that we don't want the dynamic sections loaded, since relocation
> processing and symbol resolution will likely be done by the PPU, or at
> least will happen on an image in PPU memory.  NON_ALLOC_DYN puts all
> the dynamic sections in a different place.
>
> NO_REL*_RELOCS cuts down on unnecessary linker script statements.
> Since that is a generally useful little optimisation, I'm committing
> it now, before the SPU dynamic support is ready.  I haven't enabled
> this for all ELF targets, only those that use elf.sc and have no hint
> that they might support both REL and RELA relocs.
>
> 	* scripttempl/elf.sc (NO_REL_RELOCS, NO_RELA_RELOCS, NON_ALLOC_DYN): 
> 	Handle these defines.
> 	* emulparams/criself.sh, * emulparams/crislinux.sh,
> 	* emulparams/elf32am33lin.sh, * emulparams/elf32fr30.sh,
> 	* emulparams/elf32_i860.sh, * emulparams/elf32ip2k.sh,
> 	* emulparams/elf32mcore.sh, * emulparams/elf32ppccommon.sh,
> 	* emulparams/elf32ppcwindiss.sh, * emulparams/elf32_sparc.sh,
> 	* emulparams/elf32_spu.sh, * emulparams/elf32vax.sh,
> 	* emulparams/elf64alpha.sh, * emulparams/elf64mmix.sh,
> 	* emulparams/elf64ppc.sh, * emulparams/elf64_s390.sh,
> 	* emulparams/elf64_sparc.sh, * emulparams/elf_s390.sh,
> 	* emulparams/elf_x86_64.sh, * emulparams/h8300elf.sh,
> 	* emulparams/hppa64linux.sh, * emulparams/hppalinux.sh,
> 	* emulparams/m68kelf.sh, * emulparams/mn10200.sh,
> 	* emulparams/pjelf.sh, * emulparams/ppclynx.sh,
> 	* emulparams/shelf32.sh, * emulparams/shelf_nto.sh,
> 	* emulparams/shelf.sh, * emulparams/shelf_vxworks.sh,
> 	* emulparams/shlelf32_linux.sh, * emulparams/shlelf_linux.sh,
> 	* emulparams/shlelf_nto.sh (NO_REL_RELOCS): Set.
> 	* emulparams/arcelf.sh, * emulparams/elf32_i960.sh,
> 	* emulparams/elf32openrisc.sh, * emulparams/elf_i386_be.sh,
> 	* emulparams/elf_i386_ldso.sh, * emulparams/elf_i386.sh,
> 	* emulparams/elf_i386_vxworks.sh, * emulparams/i386lynx.sh,
> 	* emulparams/i386moss.sh, * emulparams/i386nto.sh,
> 	* emulparams/or32elf.sh, * emulparams/scoreelf.sh (NO_RELA_RELOCS): Set.

I've committed the following patch to put this into the elfxtensa.sc scripts.

2008-11-03  Bob Wilson  <bob.wilson@acm.org>

	* emulparams/elf32xtensa.sh (NO_REL_RELOCS): Set.
	* scripttempl/elfxtensa.sc (NO_REL_RELOCS, NO_RELA_RELOCS)
	(NON_ALLOC_DYN): Import changes from elf.sc.

Index: emulparams/elf32xtensa.sh
===================================================================
RCS file: /cvs/src/src/ld/emulparams/elf32xtensa.sh,v
retrieving revision 1.12
diff -u -r1.12 elf32xtensa.sh
--- emulparams/elf32xtensa.sh	9 Aug 2007 11:02:24 -0000	1.12
+++ emulparams/elf32xtensa.sh	3 Nov 2008 18:28:51 -0000
@@ -4,6 +4,7 @@
 OUTPUT_FORMAT=undefined
 BIG_OUTPUT_FORMAT="elf32-xtensa-be"
 LITTLE_OUTPUT_FORMAT="elf32-xtensa-le"
+NO_REL_RELOCS=yes
 TEXT_START_ADDR=0x400000
 MAXPAGESIZE="CONSTANT (MAXPAGESIZE)"
 ARCH=xtensa
Index: scripttempl/elfxtensa.sc
===================================================================
RCS file: /cvs/src/src/ld/scripttempl/elfxtensa.sc,v
retrieving revision 1.16
diff -u -r1.16 elfxtensa.sc
--- scripttempl/elfxtensa.sc	18 Jan 2008 22:49:38 -0000	1.16
+++ scripttempl/elfxtensa.sc	3 Nov 2008 18:28:51 -0000
@@ -36,6 +36,9 @@
 #	DATA_PLT - .plt should be in data segment, not text segment.
 #	PLT_BEFORE_GOT - .plt just before .got when .plt is in data segement.
 #	BSS_PLT - .plt should be in bss segment
+#	NO_REL_RELOCS - Don't include .rel.* sections in script
+#	NO_RELA_RELOCS - Don't include .rela.* sections in script
+#	NON_ALLOC_DYN - Place dynamic sections after data segment.
 #	TEXT_DYNAMIC - .dynamic in text segment, not data segment.
 #	EMBEDDED - whether this is for an embedded system. 
 #	SHLIB_TEXT_START_ADDR - if set, add to SIZEOF_HEADERS to set
@@ -282,6 +285,11 @@
   ${CREATE_PIE+${RELOCATING+. = ${SHLIB_TEXT_START_ADDR:-0} + SIZEOF_HEADERS;}}
   ${INITIAL_READONLY_SECTIONS}
   .note.gnu.build-id : { *(.note.gnu.build-id) }
+EOF
+
+test -n "${RELOCATING+0}" || unset NON_ALLOC_DYN
+test -z "${NON_ALLOC_DYN}" || TEXT_DYNAMIC=
+cat > ldscripts/dyntmp.$$ <<EOF
   ${TEXT_DYNAMIC+${DYNAMIC}}
   .hash         ${RELOCATING-0} : { *(.hash) }
   .gnu.hash     ${RELOCATING-0} : { *(.gnu.hash) }
@@ -290,10 +298,10 @@
   .gnu.version  ${RELOCATING-0} : { *(.gnu.version) }
   .gnu.version_d ${RELOCATING-0}: { *(.gnu.version_d) }
   .gnu.version_r ${RELOCATING-0}: { *(.gnu.version_r) }
-
 EOF
+
 if [ "x$COMBRELOC" = x ]; then
-  COMBRELOCCAT=cat
+  COMBRELOCCAT="cat >> ldscripts/dyntmp.$$"
 else
   COMBRELOCCAT="cat > $COMBRELOC"
 fi
@@ -330,27 +338,45 @@
   .rela.bss     ${RELOCATING-0} : { *(.rela.bss${RELOCATING+ .rela.bss.* .rela.gnu.linkonce.b.*}) }
   ${REL_LARGE}
 EOF
+
 if [ -n "$COMBRELOC" ]; then
-cat <<EOF
+cat >> ldscripts/dyntmp.$$ <<EOF
   .rel.dyn      ${RELOCATING-0} :
     {
 EOF
-sed -e '/^[ 	]*[{}][ 	]*$/d;/:[ 	]*$/d;/\.rela\./d;s/^.*: { *\(.*\)}$/      \1/' $COMBRELOC
-cat <<EOF
+sed -e '/^[ 	]*[{}][ 	]*$/d;/:[ 	]*$/d;/\.rela\./d;s/^.*: { *\(.*\)}$/      \1/' $COMBRELOC >> ldscripts/dyntmp.$$
+cat >> ldscripts/dyntmp.$$ <<EOF
     }
   .rela.dyn     ${RELOCATING-0} :
     {
 EOF
-sed -e '/^[ 	]*[{}][ 	]*$/d;/:[ 	]*$/d;/\.rel\./d;s/^.*: { *\(.*\)}/      \1/' $COMBRELOC
-cat <<EOF
+sed -e '/^[ 	]*[{}][ 	]*$/d;/:[ 	]*$/d;/\.rel\./d;s/^.*: { *\(.*\)}/      \1/' $COMBRELOC >> ldscripts/dyntmp.$$
+cat >> ldscripts/dyntmp.$$ <<EOF
     }
 EOF
 fi
-cat <<EOF
+
+cat >> ldscripts/dyntmp.$$ <<EOF
   .rel.plt      ${RELOCATING-0} : { *(.rel.plt) }
   .rela.plt     ${RELOCATING-0} : { *(.rela.plt) }
   ${OTHER_PLT_RELOC_SECTIONS}
+EOF
 
+if test -z "${NON_ALLOC_DYN}"; then
+  if test -z "${NO_REL_RELOCS}${NO_RELA_RELOCS}"; then
+    cat ldscripts/dyntmp.$$
+  else
+    if test -z "${NO_REL_RELOCS}"; then
+      sed -e '/^[ 	]*\.rela\.[^}]*$/,/}/d' -e '/^[ 	]*\.rela\./d' ldscripts/dyntmp.$$
+    fi
+    if test -z "${NO_RELA_RELOCS}"; then
+      sed -e '/^[ 	]*\.rel\.[^}]*$/,/}/d' -e '/^[ 	]*\.rel\./d' ldscripts/dyntmp.$$
+    fi
+  fi
+  rm -f ldscripts/dyntmp.$$
+fi
+
+cat <<EOF
   ${RELOCATING-$INIT_LIT}
   ${RELOCATING-$INIT}
 
@@ -484,7 +510,23 @@
   ${RELOCATING+${OTHER_END_SYMBOLS}}
   ${RELOCATING+${END_SYMBOLS-${USER_LABEL_PREFIX}_end = .; PROVIDE (${USER_LABEL_PREFIX}end = .);}}
   ${RELOCATING+${DATA_SEGMENT_END}}
+EOF
 
+if test -n "${NON_ALLOC_DYN}"; then
+  if test -z "${NO_REL_RELOCS}${NO_RELA_RELOCS}"; then
+    cat ldscripts/dyntmp.$$
+  else
+    if test -z "${NO_REL_RELOCS}"; then
+      sed -e '/^[ 	]*\.rela\.[^}]*$/,/}/d' -e '/^[ 	]*\.rela\./d' ldscripts/dyntmp.$$
+    fi
+    if test -z "${NO_RELA_RELOCS}"; then
+      sed -e '/^[ 	]*\.rel\.[^}]*$/,/}/d' -e '/^[ 	]*\.rel\./d' ldscripts/dyntmp.$$
+    fi
+  fi
+  rm -f ldscripts/dyntmp.$$
+fi
+
+cat <<EOF
   /* Stabs debugging sections.  */
   .stab          0 : { *(.stab) }
   .stabstr       0 : { *(.stabstr) }