Import the DragonFly BSD commit 4f0bc915b65fcf5a23214f6d221d65c80be68ad4

by John Marino <draco@marino.st>, with the following (edited) commit
message
Date: Sat, 24 Mar 2012 06:40:50 +0100
Subject: [PATCH 1/1] rtld: Implement DT_RUNPATH and -z nodefaultlib

DT_RUNPATH is incorrectly being considered as an alias of DT_RPATH.  The
purpose of DT_RUNPATH is to have two different types of rpath: one that
can be overridden by the environment variable LD_LIBRARY_PATH and one that
can't.  With the currently implementation, LD_LIBRARY_PATH will always
trump any embedded rpath or runpath tags.

Current path search order by rtld:
==================================
LD_LIBRARY_PATH
DT_RPATH / DT_RUNPATH (always the same)
ldconfig hints file (default: /var/run/ld-elf.so.hints)
/usr/lib

New path search order by rtld:
==============================
DT_RPATH of the calling object if no DT_RUNPATH
DT_RPATH of the main binary if no DT_RUNPATH and binary isn't calling obj
LD_LIBRARY_PATH
DT_RUNPATH
ldconfig hints file
/usr/lib

The new path search matches how the linux runtime loader works.  The other
major added feature is support for linker flag "-z nodefaultlib".  When
this flag is passed to the linker, rtld will skip all references to the
standard library search path ("/usr/lib" in this case but it could handle
more color delimited paths) except in DT_RPATH and DT_RUNPATH.

New path search order by rtld with -z nodefaultlib flag set:
============================================================
DT_RPATH of the calling object if no DT_RUNPATH
DT_RPATH of the main binary if no DT_RUNPATH and binary isn't calling obj
LD_LIBRARY_PATH
DT_RUNPATH
ldconfig hints file (skips all references to /usr/lib)

FreeBSD notes:
- we fixed some bugs which were submitted to DragonFly and merged there
  as commit 1ff8a2bd3eb6e5587174c6a983303ea3a79e0002;
- we added LD_LIBRARY_PATH_RPATH environment variable to switch to
  the previous behaviour of considering DT_RPATH a synonym for DT_RUNPATH;
- the FreeBSD default search path is /lib:/usr/lib and not /usr/lib.

Reviewed by:   kan
MFC after:     1 month
MFC note:      flip the ld_library_path_rpath default value for stable/9

1 files changed, 46 insertions, 7 deletions

diff --git a/libexec/rtld-elf/rtld.1 b/libexec/rtld-elf/rtld.1
index f77b150..703a462 100644
--- a/libexec/rtld-elf/rtld.1
+++ b/libexec/rtld-elf/rtld.1
@@ -28,7 +28,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd April 1, 2009
+.Dd June 28, 2012
 .Dt RTLD 1
 .Os
 .Sh NAME
@@ -86,14 +86,39 @@ dynamic linker.
 After the dynamic linker has finished loading,
 relocating, and initializing the program and its required shared
 objects, it transfers control to the entry point of the program.
+The following search order is used to locate required shared objects:
 .Pp
-To locate the required shared objects in the file system,
-.Nm
-may use a
-.Dq hints
-file prepared by the
+.Bl -enum -offset indent -compact
+.It
+.Dv DT_RPATH
+of the referencing object unless that object also contains a
+.Dv DT_RUNPATH
+tag
+.It
+.Dv DT_RPATH
+of the program unless the referencing object contains a
+.Dv DT_RUNPATH
+tag
+.It
+Path indicated by
+.Ev LD_LIBRARY_PATH
+environment variable
+.It
+.Dv DT_RUNPATH
+of the referencing object
+.It
+Hints file produced by the
 .Xr ldconfig 8
-utility.
+utility
+.It
+The
+.Pa /lib
+and
+.Pa /usr/lib
+directories, unless the referencing object was linked using the
+.Dq Fl z Ar nodefaultlib
+option
+.El
 .Pp
 The
 .Nm
@@ -143,6 +168,20 @@ This variable is unset for set-user-ID and set-group-ID programs.
 A colon separated list of directories, overriding the default search path
 for shared libraries.
 This variable is unset for set-user-ID and set-group-ID programs.
+.It Ev LD_LIBRARY_PATH_RPATH
+If the variable is specified and has a value starting with
+any of \'y\', \'Y\' or \'1\' symbols, the path specified by
+.Ev LD_LIBRARY_PATH
+variable is allowed to override the path from
+.Dv DT_RPATH
+for binaries which does not contain
+.Dv DT_RUNPATH
+tag.
+For such binaries, when the variable
+.Ev LD_LIBRARY_PATH_RPATH
+is set,
+.Dq Fl z Ar nodefaultlib
+link-time option is ignored as well.
 .It Ev LD_PRELOAD
 A list of shared libraries, separated by colons and/or white space,
 to be linked in before any