From b5666f2f09f4ae51777c3705202b25f325df0702 Mon Sep 17 00:00:00 2001 From: Alan Modra Date: Sun, 23 Jan 2005 05:36:37 +0000 Subject: [PATCH] * ld.texinfo (Location Counter ): Document effects of orphan section placement, and ". = ." workaround. * Makefile.in: Regenerate. --- ld/ChangeLog | 6 +++++ ld/Makefile.in | 4 ++-- ld/ld.texinfo | 70 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++- 3 files changed, 77 insertions(+), 3 deletions(-) diff --git a/ld/ChangeLog b/ld/ChangeLog index d261fe2..52c5c3d 100644 --- a/ld/ChangeLog +++ b/ld/ChangeLog @@ -1,3 +1,9 @@ +2005-01-23 Alan Modra + + * ld.texinfo (Location Counter ): Document + effects of orphan section placement, and ". = ." workaround. + * Makefile.in: Regenerate. + 2005-01-22 Richard Sandiford * emulparams/elf32bmip.sh (OTHER_GOT_SECTIONS): Add ". = .;". diff --git a/ld/Makefile.in b/ld/Makefile.in index eb2f110..25f21e0 100644 --- a/ld/Makefile.in +++ b/ld/Makefile.in @@ -629,7 +629,7 @@ deffilep.c ldgram.c ldlex.c DISTFILES = $(DIST_COMMON) $(SOURCES) $(HEADERS) $(TEXINFOS) $(EXTRA_DIST) -TAR = gtar +TAR = tar GZIP_ENV = --best SOURCES = $(ld_new_SOURCES) $(EXTRA_ld_new_SOURCES) OBJECTS = $(ld_new_OBJECTS) @@ -1111,7 +1111,7 @@ distclean-generic: -test -z "$(DISTCLEANFILES)" || rm -f $(DISTCLEANFILES) maintainer-clean-generic: - -test -z "ldlexcdeffilephdeffilepcldgramhldgramc$(MAINTAINERCLEANFILES)" || rm -f ldlexc deffileph deffilepc ldgramh ldgramc $(MAINTAINERCLEANFILES) + -test -z "ldlex.cdeffilep.hdeffilep.cldgram.hldgram.c$(MAINTAINERCLEANFILES)" || rm -f ldlex.c deffilep.h deffilep.c ldgram.h ldgram.c $(MAINTAINERCLEANFILES) mostlyclean-am: mostlyclean-hdr mostlyclean-noinstPROGRAMS \ mostlyclean-compile mostlyclean-libtool \ mostlyclean-aminfo mostlyclean-tags mostlyclean-generic \ diff --git a/ld/ld.texinfo b/ld/ld.texinfo index 11628a6..9897530 100644 --- a/ld/ld.texinfo +++ b/ld/ld.texinfo @@ -2769,7 +2769,7 @@ The first case will define @var{symbol} to the value of defined, and the value will be adjusted accordingly. The special symbol name @samp{.} indicates the location counter. You -may only use this within a @code{SECTIONS} command. +may only use this within a @code{SECTIONS} command. @xref{Location Counter}. The semicolon after @var{expression} is required. @@ -4381,6 +4381,74 @@ and it will have an extra 0x600 bytes worth of space after the end of the values from the @samp{.data} input sections and before the end of the @samp{.data} output section itself. +@cindex dot outside sections +Setting symbols to the value of the location counter outside of an +output section statement can result in unexpected values if the linker +needs to place orphan sections. For example, given the following: + +@smallexample +SECTIONS +@{ + start_of_text = . ; + .text: @{ *(.text) @} + end_of_text = . ; + + start_of_data = . ; + .data: @{ *(.data) @} + end_of_data = . ; +@} +@end smallexample + +If the linker needs to place some input section, e.g. @code{.rodata}, +not mentioned in the script, it might choose to place that section +between @code{.text} and @code{.data}. You might think the linker +should place @code{.rodata} on the blank line in the above script, but +blank lines are of no particular significance to the linker. As well, +the linker doesn't associate the above symbol names with their +sections. Instead, it assumes that all assignments or other +statements belong to the previous output section, except for the +special case of an assignment to @code{.}. I.e., the linker will +place the orphan @code{.rodata} section as if the script was written +as follows: + +@smallexample +SECTIONS +@{ + start_of_text = . ; + .text: @{ *(.text) @} + end_of_text = . ; + + start_of_data = . ; + .rodata: @{ *(.rodata) @} + .data: @{ *(.data) @} + end_of_data = . ; +@} +@end smallexample + +This may or may not be the script author's intention for the value of +@code{start_of_data}. One way to influence the orphan section +placement is to assign the location counter to itself, as the linker +assumes that an assignment to @code{.} is setting the start address of +a following output section and thus should be grouped with that +section. So you could write: + +@smallexample +SECTIONS +@{ + start_of_text = . ; + .text: @{ *(.text) @} + end_of_text = . ; + + . = . ; + start_of_data = . ; + .data: @{ *(.data) @} + end_of_data = . ; +@} +@end smallexample + +Now, the orphan @code{.rodata} section will be placed between +@code{end_of_text} and @code{start_of_data}. + @need 2000 @node Operators @subsection Operators -- 2.7.4