Add new NOCROSSREFS_TO linker script command

NOCROSSREFS_TO is similar to the existing NOCROSSREFS command but only
checks one direction of cross referencing.

ld/ChangeLog

	* ld.texinfo: Document NOCROSSREFS_TO script command.
	* ldlang.h (struct lang_nocrossrefs): Add onlyfirst field.
	(lang_add_nocrossref_to): New prototype.
	* ldcref.c (check_local_sym_xref): Use onlyfirst to only look for
	symbols defined in the first section.
	(check_nocrossref): Likewise.
	* ldgram.y (NOCROSSREFS_TO): New script command.
	* ldlang.c (lang_add_nocrossref): Set onlyfirst to FALSE.
	(lang_add_nocrossref_to): New function.
	* ldlex.l (NOCROSSREFS_TO): New token.
	* NEWS: Mention NOCROSSREFS_TO.
	* testsuite/ld-scripts/cross4.t: New file.
	* testsuite/ld-scripts/cross5.t: Likewise.
	* testsuite/ld-scripts/cross6.t: Likewise.
	* testsuite/ld-scripts/cross7.t: Likewise.
	* testsuite/ld-scripts/crossref.exp: Run 4 new NOCROSSREFS_TO
	tests.

1 files changed, 19 insertions, 0 deletions

diff --git a/ld/ld.texinfo b/ld/ld.texinfo
index d3d8dc6..7a2ed3a 100644
--- a/ld/ld.texinfo
+++ b/ld/ld.texinfo
@@ -3674,6 +3674,25 @@ an error and returns a non-zero exit status.  Note that the
 @code{NOCROSSREFS} command uses output section names, not input section
 names.
 
+@item NOCROSSREFS_TO(@var{tosection} @var{fromsection} @dots{})
+@kindex NOCROSSREFS_TO(@var{tosection} @var{fromsections})
+@cindex cross references
+This command may be used to tell @command{ld} to issue an error about any
+references to one section from a list of other sections.
+
+The @code{NOCROSSREFS} command is useful when ensuring that two or more
+output sections are entirely independent but there are situations where
+a one-way dependency is needed. For example, in a multi-core application
+there may be shared code that can be called from each core but for safety
+must never call back.
+
+The @code{NOCROSSREFS_TO} command takes a list of output section names.
+The first section can not be referenced from any of the other sections.
+If @command{ld} detects any references to the first section from any of
+the other sections, it reports an error and returns a non-zero exit
+status.  Note that the @code{NOCROSSREFS_TO} command uses output section
+names, not input section names.
+
 @ifclear SingleFormat
 @item OUTPUT_ARCH(@var{bfdarch})
 @kindex OUTPUT_ARCH(@var{bfdarch})