error handling in dynamic linking

some of the code is not yet used, and is in preparation for dlopen
which needs to be able to handle failure loading libraries without
terminating the program.

src/ldso/dynlink.c

@@ -12,6 +12,7 @@
 #include <errno.h>
 #include <limits.h>
 #include <elf.h>
+#include <setjmp.h>
 
 #include "reloc.h"
 
@@ -44,11 +45,14 @@ struct dso
 	ino_t ino;
 	int global;
 	int relocated;
-	char name[];
+	char *name;
+	char buf[];
 };
 
 static struct dso *head, *tail, *libc;
 static char *env_path, *sys_path;
+static int runtime;
+static jmp_buf rtld_fail;
 
 #define AUX_CNT 15
 #define DYN_CNT 34
@@ -115,6 +119,11 @@ static void do_relocs(unsigned char *base, size_t *rel, size_t rel_size, size_t
 			name = strings + sym->st_name;
 			ctx = IS_COPY(type) ? dso->next : dso;
 			sym_val = (size_t)find_sym(ctx, name, IS_PLT(type));
+			if (!sym_val && sym->st_info>>4 != STB_WEAK) {
+				if (runtime) longjmp(rtld_fail, 1);
+				dprintf(2, "%s: symbol not found\n", name);
+				_exit(127);
+			}
 			sym_size = sym->st_size;
 		}
 		do_single_reloc(reloc_addr, type, sym_val, sym_size, base, rel[2]);
@@ -308,6 +317,7 @@ static struct dso *load_library(const char *name)
 	p->ino = st.st_ino;
 	p->global = 1;
 	p->refcnt = 1;
+	p->name = p->buf;
 	strcpy(p->name, name);
 
 	tail->next = p;
@@ -323,7 +333,12 @@ static void load_deps(struct dso *p)
 	for (; p; p=p->next) {
 		for (i=0; p->dynv[i]; i+=2) {
 			if (p->dynv[i] != DT_NEEDED) continue;
-			load_library(p->strings + p->dynv[i+1]);
+			if (!load_library(p->strings + p->dynv[i+1])) {
+				if (runtime) longjmp(rtld_fail, 1);
+				dprintf(2, "%s: %m (needed by %s)\n",
+					p->strings + p->dynv[i+1], p->name);
+				_exit(127);
+			}
 		}
 	}
 }
@@ -395,6 +410,7 @@ void *__dynlink(int argc, char **argv, size_t *got)
 		.hashtab = (void *)(app_dyn[DT_HASH]),
 		.syms = (void *)(app_dyn[DT_SYMTAB]),
 		.dynv = (void *)(phdr->p_vaddr),
+		.name = argv[0],
 		.next = &lib
 	};
 
@@ -404,6 +420,7 @@ void *__dynlink(int argc, char **argv, size_t *got)
 		.hashtab = (void *)(aux[AT_BASE]+lib_dyn[DT_HASH]),
 		.syms = (void *)(aux[AT_BASE]+lib_dyn[DT_SYMTAB]),
 		.dynv = (void *)(got[0]),
+		.name = "libc.so",
 		.relocated = 1
 	};