Description from Dan:

Another handy libmap patch.  Lets you do stuff like this:

	LD_LIBMAP="libpthread.so.1=libthr.so.1" mythreadedapp

	If you already have a program-specific override in libmap.conf, note
	that you must use a program-specific override in LD_LIBMAP:

	LD_LIBMAP="[mythreadedapp],libpthread.so.1=libthr.so.1" mythreadedapp

PR:		bin/74471
Submitted by:	Dan Nelson <dnelson AT allantgroup.com>
MFC after:	2 weeks

libexec/rtld-elf/libmap.c

@@ -38,32 +38,70 @@ struct lmp {
 	TAILQ_ENTRY(lmp) lmp_link;
 };
 
+static int	lm_count;
+
+static void		lmc_parse	(FILE *);
 static void		lm_add		(const char *, const char *, const char *);
 static void		lm_free		(struct lm_list *);
 static char *		lml_find	(struct lm_list *, const char *);
 static struct lm_list *	lmp_find	(const char *);
 static struct lm_list *	lmp_init	(char *);
 static const char * quickbasename	(const char *);
+static int	readstrfn	(void * cookie, char *buf, int len);
+static int	closestrfn	(void * cookie);
 
 #define	iseol(c)	(((c) == '#') || ((c) == '\0') || \
 			 ((c) == '\n') || ((c) == '\r'))
 
 int
-lm_init (void)
+lm_init (char *libmap_override)
 {
 	FILE	*fp;
-	char	*cp;
-	char	*f, *t, *p, *c;
-	char	prog[MAXPATHLEN];
-	char	line[MAXPATHLEN + 2];
 
-	dbg("%s()", __func__);
+	dbg("%s(\"%s\")", __func__, libmap_override);
 
 	TAILQ_INIT(&lmp_head);
 
-	if ((fp = fopen(_PATH_LIBMAP_CONF, "r")) == NULL)
-		return (1);
+	fp = fopen(_PATH_LIBMAP_CONF, "r");
+	if (fp) {
+		lmc_parse(fp);
+		fclose(fp);
+	}
 
+	if (libmap_override) {
+		char	*p;
+		/* do some character replacement to make $LIBMAP look like a
+		   text file, then "open" it with funopen */
+		libmap_override = xstrdup(libmap_override);
+
+		for (p = libmap_override; *p; p++) {
+			switch (*p) {
+				case '=':
+					*p = ' '; break;
+				case ',':
+					*p = '\n'; break;
+			}
+		}
+		fp = funopen(libmap_override, readstrfn, NULL, NULL, closestrfn);
+		if (fp) {
+			lmc_parse(fp);
+			fclose(fp);
+		}
+	}
+
+	return (lm_count == 0);
+}
+
+static void
+lmc_parse (FILE *fp)
+{
+	char	*cp;
+	char	*f, *t, *c, *p;
+	char	prog[MAXPATHLEN];
+	char	line[MAXPATHLEN + 2];
+
+	dbg("%s(%p)", __func__, fp);
+	
 	p = NULL;
 	while ((cp = fgets(line, MAXPATHLEN + 1, fp)) != NULL) {
 		t = f = c = NULL;
@@ -134,8 +172,6 @@ lm_init (void)
 		*cp = '\0';
 		lm_add(p, f, t);
 	}
-	fclose(fp);
-	return (0);
 }
 
 static void
@@ -190,6 +226,7 @@ lm_add (const char *p, const char *f, const char *t)
 	lm->f = xstrdup(f);
 	lm->t = xstrdup(t);
 	TAILQ_INSERT_HEAD(lml, lm, lm_link);
+	lm_count++;
 }
 
 char *
@@ -304,3 +341,31 @@ quickbasename (const char *path)
 	}
 	return (p);
 }
+
+static int
+readstrfn(void * cookie, char *buf, int len)
+{
+	static char	*current;
+	static int	left;
+	int 	copied;
+	
+	copied = 0;
+	if (!current) {
+		current = cookie;
+		left = strlen(cookie);
+	}
+	while (*current && left && len) {
+		*buf++ = *current++;
+		left--;
+		len--;
+		copied++;
+	}
+	return copied;
+}
+
+static int
+closestrfn(void * cookie)
+{
+	free(cookie);
+	return 0;
+}

libexec/rtld-elf/libmap.h

@@ -2,7 +2,7 @@
  * $FreeBSD$
  */
 
-int	lm_init (void);
+int	lm_init (char *);
 void	lm_fini (void);
 char *	lm_find (const char *, const char *);
 #ifdef COMPAT_32BIT

libexec/rtld-elf/rtld.1

@@ -93,9 +93,22 @@ If set
 .Nm
 will print a table containing all relocations before symbol
 binding and relocation.
+.It Ev LD_LIBMAP
+A library replacement list in the same format as
+.Xr libmap.conf 5 .
+For convenience, the characters
+.Ql =
+and
+.Ql \&,
+can be used instead of a space and a newline.
+This variable is parsed after 
+.Xr libmap.conf 5 ,
+and will override its entries.
 .It Ev LD_LIBMAP_DISABLE
 If set, disables the use of
-.Xr libmap.conf 5 .
+.Xr libmap.conf 5 
+and
+.Ev LD_LIBMAP .
 .It Ev LD_LIBRARY_PATH
 A colon separated list of directories, overriding the default search path
 for shared libraries.

libexec/rtld-elf/rtld.c

@@ -137,6 +137,7 @@ void r_debug_state(struct r_debug*, struct link_map*);
 static char *error_message;	/* Message for dlerror(), or NULL */
 struct r_debug r_debug;		/* for GDB; */
 static bool libmap_disable;	/* Disable libmap */
+static char *libmap_override;	/* Maps to use in addition to libmap.conf */
 static bool trust;		/* False for setuid and setgid programs */
 static char *ld_bind_now;	/* Environment variable for immediate binding */
 static char *ld_debug;		/* Environment variable for debugging */
@@ -289,6 +290,7 @@ _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
     if (trust) {
 	ld_debug = getenv(LD_ "DEBUG");
 	libmap_disable = getenv(LD_ "LIBMAP_DISABLE") != NULL;
+	libmap_override = getenv(LD_ "LIBMAP");
 	ld_library_path = getenv(LD_ "LIBRARY_PATH");
 	ld_preload = getenv(LD_ "PRELOAD");
     }
@@ -363,7 +365,7 @@ _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
     sym_zero.st_shndx = SHN_UNDEF;
 
     if (!libmap_disable)
-        libmap_disable = (bool)lm_init();
+        libmap_disable = (bool)lm_init(libmap_override);
 
     dbg("loading LD_PRELOAD libraries");
     if (load_preload_objects() == -1)