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* ld.texinfo (Location Counter <dot outside sections>): Document

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effects of orphan section placement, and ". = ." workaround.
	* Makefile.in: Regenerate.
This commit is contained in:
Alan Modra 2005-01-23 05:36:37 +00:00
parent 059198c19d
commit b5666f2f09
3 changed files with 77 additions and 3 deletions
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6
ld/ChangeLog
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@ -1,3 +1,9 @@
2005-01-23 Alan Modra <amodra@bigpond.net.au>
* ld.texinfo (Location Counter <dot outside sections>): Document
effects of orphan section placement, and ". = ." workaround.
* Makefile.in: Regenerate.
2005-01-22 Richard Sandiford <rsandifo@redhat.com>
* emulparams/elf32bmip.sh (OTHER_GOT_SECTIONS): Add ". = .;".

4
ld/Makefile.in
View file

@ -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 \

70
ld/ld.texinfo
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@ -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