Pay attention to the environment variable "LD_IGNORE_MISSING_OBJECTS".

If it is set to a nonempty string, then simply skip any missing
shared libraries.  This came up in a discussion long ago as a
potentially useful feature at sysinstall time.  For example, an
X11 utility could be used without the X libraries being present,
provided the utility had a mode in which no X functions were actually
called.

4 files changed, 86 insertions, 3 deletions

diff --git a/libexec/rtld-aout/rtld.1 b/libexec/rtld-aout/rtld.1
index 35d1c88..a3734f9 100644
--- a/libexec/rtld-aout/rtld.1
+++ b/libexec/rtld-aout/rtld.1
@@ -106,7 +106,7 @@ library-name, major-version-number, minor-version-number
 recognises a number of environment variables that can be used to modify
 its behaviour as follows:
 .Pp
-.Bl -tag -width "LD_TRACE_LOADED_OBJECTS_PROGNAME"
+.Bl -tag -width "LD_IGNORE_MISSING_OBJECTS"
 .It Ev LD_LIBRARY_PATH
 A colon separated list of directories, overriding the default search path
 for shared libraries.
@@ -134,6 +134,30 @@ object. This is usually indicative of an incorrectly built library.
 When set to a nonempty string, no warning messages of any kind are
 issued. Normally, a warning is given if satisfactorily versioned
 library could not be found.
+.It Ev LD_IGNORE_MISSING_OBJECTS
+When set to a nonempty string, makes it a nonfatal condition if
+one or more required shared objects cannot be loaded.
+Loading and execution proceeds using the objects that are
+available.
+A warning is produced for each missing object, unless the environment
+variable
+.Ev LD_SUPPRESS_WARNINGS
+is set to a nonempty string.
+.Pp
+This is ignored for set-user-ID and set-group-ID programs.
+.Pp
+Missing shared objects can be ignored without errors if all the
+following conditions hold:
+.Bl -bullet
+.It
+They do not supply definitions for any required data symbols.
+.It
+No functions defined by them are called during program execution.
+.It
+The environment variable
+.Ev LD_BIND_NOW
+is unset or is set to the empty string.
+.El
 .It Ev LD_TRACE_LOADED_OBJECTS
 When set to a nonempty string, causes
 .Nm
diff --git a/libexec/rtld-aout/rtld.1aout b/libexec/rtld-aout/rtld.1aout
index 35d1c88..a3734f9 100644
--- a/libexec/rtld-aout/rtld.1aout
+++ b/libexec/rtld-aout/rtld.1aout
@@ -106,7 +106,7 @@ library-name, major-version-number, minor-version-number
 recognises a number of environment variables that can be used to modify
 its behaviour as follows:
 .Pp
-.Bl -tag -width "LD_TRACE_LOADED_OBJECTS_PROGNAME"
+.Bl -tag -width "LD_IGNORE_MISSING_OBJECTS"
 .It Ev LD_LIBRARY_PATH
 A colon separated list of directories, overriding the default search path
 for shared libraries.
@@ -134,6 +134,30 @@ object. This is usually indicative of an incorrectly built library.
 When set to a nonempty string, no warning messages of any kind are
 issued. Normally, a warning is given if satisfactorily versioned
 library could not be found.
+.It Ev LD_IGNORE_MISSING_OBJECTS
+When set to a nonempty string, makes it a nonfatal condition if
+one or more required shared objects cannot be loaded.
+Loading and execution proceeds using the objects that are
+available.
+A warning is produced for each missing object, unless the environment
+variable
+.Ev LD_SUPPRESS_WARNINGS
+is set to a nonempty string.
+.Pp
+This is ignored for set-user-ID and set-group-ID programs.
+.Pp
+Missing shared objects can be ignored without errors if all the
+following conditions hold:
+.Bl -bullet
+.It
+They do not supply definitions for any required data symbols.
+.It
+No functions defined by them are called during program execution.
+.It
+The environment variable
+.Ev LD_BIND_NOW
+is unset or is set to the empty string.
+.El
 .It Ev LD_TRACE_LOADED_OBJECTS
 When set to a nonempty string, causes
 .Nm
diff --git a/libexec/rtld-aout/rtld.c b/libexec/rtld-aout/rtld.c
index 6321a11..b14e1fb 100644
--- a/libexec/rtld-aout/rtld.c
+++ b/libexec/rtld-aout/rtld.c
@@ -188,6 +188,7 @@ static int		careful;
 static int		anon_fd = -1;
 
 static char		*ld_bind_now;
+static char		*ld_ignore_missing_objects;
 static char		*ld_library_path;
 static char		*ld_preload;
 static char		*ld_tracing;
@@ -869,6 +870,15 @@ map_sods(parent)
 			 * "not found" message.
 			 */
 			(void)alloc_link_map(NULL, sodp, parent, 0, 0);
+		} else if (ld_ignore_missing_objects) {
+			char *msg;
+			/*
+			 * Call __dlerror() even it we're not going to use
+			 * the message, in order to clear the saved message.
+			 */
+			msg = __dlerror();  /* Should never be NULL */
+			if (!ld_suppress_warnings)
+				warnx("warning: %s", msg);
 		} else  /* Give up */
 			break;
 
@@ -2022,6 +2032,7 @@ struct env_scan_tab {
 } scan_tab[] = {
 	L("LD_LIBRARY_PATH=",		1, &ld_library_path)
 	L("LD_PRELOAD=",		1, &ld_preload)
+	L("LD_IGNORE_MISSING_OBJECTS=",	1, &ld_ignore_missing_objects)
 	L("LD_TRACE_LOADED_OBJECTS=",	0, &ld_tracing)
 	L("LD_BIND_NOW=",		0, &ld_bind_now)
 	L("LD_SUPPRESS_WARNINGS=",	0, &ld_suppress_warnings)
diff --git a/libexec/rtld-elf/rtld.1 b/libexec/rtld-elf/rtld.1
index 35d1c88..a3734f9 100644
--- a/libexec/rtld-elf/rtld.1
+++ b/libexec/rtld-elf/rtld.1
@@ -106,7 +106,7 @@ library-name, major-version-number, minor-version-number
 recognises a number of environment variables that can be used to modify
 its behaviour as follows:
 .Pp
-.Bl -tag -width "LD_TRACE_LOADED_OBJECTS_PROGNAME"
+.Bl -tag -width "LD_IGNORE_MISSING_OBJECTS"
 .It Ev LD_LIBRARY_PATH
 A colon separated list of directories, overriding the default search path
 for shared libraries.
@@ -134,6 +134,30 @@ object. This is usually indicative of an incorrectly built library.
 When set to a nonempty string, no warning messages of any kind are
 issued. Normally, a warning is given if satisfactorily versioned
 library could not be found.
+.It Ev LD_IGNORE_MISSING_OBJECTS
+When set to a nonempty string, makes it a nonfatal condition if
+one or more required shared objects cannot be loaded.
+Loading and execution proceeds using the objects that are
+available.
+A warning is produced for each missing object, unless the environment
+variable
+.Ev LD_SUPPRESS_WARNINGS
+is set to a nonempty string.
+.Pp
+This is ignored for set-user-ID and set-group-ID programs.
+.Pp
+Missing shared objects can be ignored without errors if all the
+following conditions hold:
+.Bl -bullet
+.It
+They do not supply definitions for any required data symbols.
+.It
+No functions defined by them are called during program execution.
+.It
+The environment variable
+.Ev LD_BIND_NOW
+is unset or is set to the empty string.
+.El
 .It Ev LD_TRACE_LOADED_OBJECTS
 When set to a nonempty string, causes
 .Nm