sync with OpenBSD -current

libexec/ld.so/loader.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: loader.c,v 1.218 2023/12/19 16:13:22 deraadt Exp $ */
+/*	$OpenBSD: loader.c,v 1.219 2024/01/14 09:39:03 kettenis Exp $ */
 
 /*
  * Copyright (c) 1998 Per Fogelstrom, Opsycon AB
@@ -70,6 +70,7 @@ int _dl_trust __relro = 0;
 char **_dl_libpath __relro = NULL;
 const char **_dl_argv __relro = NULL;
 int _dl_argc __relro = 0;
+const char *_dl_libcname;
 
 char *_dl_preload __boot_data = NULL;
 char *_dl_tracefmt1 __boot_data = NULL;
@@ -358,6 +359,31 @@ _dl_load_dep_libs(elf_object_t *object, int flags, int booting)
 				if (dynp->d_tag == DT_NEEDED)
 					liblist[loop++].dynp = dynp;
 
+			/*
+			 * We can't support multiple versions of libc
+			 * in a single process.  So remember the first
+			 * libc SONAME we encounter as a dependency
+			 * and use it in further loads of libc.  In
+			 * practice this means we will always use the
+			 * libc version that the binary was linked
+			 * against.  This isn't entirely correct, but
+			 * it will keep most binaries running when
+			 * transitioning over a libc major bump.
+			 */
+			if (_dl_libcname == NULL) {
+				for (loop = 0; loop < libcount; loop++) {
+					const char *libname;
+					libname = dynobj->dyn.strtab;
+					libname +=
+					    liblist[loop].dynp->d_un.d_val;
+					if (_dl_strncmp(libname,
+					    "libc.so.", 8) == 0) {
+						_dl_libcname = libname;
+						break;
+					}
+				}
+			}
+
 			/* Randomize these */
 			for (loop = 0; loop < libcount; loop++)
 				randomlist[loop] = loop;
@@ -380,6 +406,10 @@ _dl_load_dep_libs(elf_object_t *object, int flags, int booting)
 				    liblist[randomlist[loop]].dynp->d_un.d_val;
 				DL_DEB(("loading: %s required by %s\n", libname,
 				    dynobj->load_name));
+				if (_dl_strncmp(libname, "libc.so.", 8) == 0) {
+					if (_dl_libcname)
+						libname = _dl_libcname;
+				}
 				depobj = _dl_load_shlib(libname, dynobj,
 				    OBJTYPE_LIB, depflags, nodelete);
 				if (depobj == 0) {