X-Git-Url: http://nsz.repo.hu/git/?p=musl;a=blobdiff_plain;f=src%2Fldso%2Fdynlink.c;h=6ffda49cf42c545b889d53ef0bda9a7cfb313f18;hp=b308b875f995c0a06e5b24dfafc9cc40f3a0cd1a;hb=731e8ffdcf6877c04092aa9fbd2b17907b8846c7;hpb=b7f6e0c6f848b7a8c64b3f7b72014b48a9923729

diff --git a/src/ldso/dynlink.c b/src/ldso/dynlink.c
index b308b875..6ffda49c 100644
--- a/src/ldso/dynlink.c
+++ b/src/ldso/dynlink.c
@@ -12,8 +12,15 @@
 #include <errno.h>
 #include <limits.h>
 #include <elf.h>
+#include <setjmp.h>
+#include <pthread.h>
+#include <ctype.h>
+#include <dlfcn.h>
 
-#include "reloc.h"
+static int errflag;
+static char errbuf[128];
+
+#ifdef SHARED
 
 #if ULONG_MAX == 0xffffffff
 typedef Elf32_Ehdr Ehdr;
@@ -29,28 +36,56 @@ typedef Elf64_Sym Sym;
 #define R_SYM(x) ((x)>>32)
 #endif
 
-struct dso
-{
+struct debug {
+	int ver;
+	void *head;
+	void (*bp)(void);
+	int state;
+	void *base;
+};
+
+struct dso {
+	unsigned char *base;
+	char *name;
+	size_t *dynv;
 	struct dso *next, *prev;
+
 	int refcnt;
-	size_t *dynv;
 	Sym *syms;
 	uint32_t *hashtab;
+	uint32_t *ghashtab;
 	char *strings;
-	unsigned char *base;
 	unsigned char *map;
 	size_t map_len;
 	dev_t dev;
 	ino_t ino;
-	int global;
-	int relocated;
-	char name[];
+	signed char global;
+	char relocated;
+	char constructed;
+	struct dso **deps;
+	char *shortname;
+	char buf[];
 };
 
-static struct dso *head, *tail, *libc;
-static int trust_env;
+#include "reloc.h"
+
+void __init_ssp(size_t *);
 
-#define AUX_CNT 15
+static struct dso *head, *tail, *libc;
+static char *env_path, *sys_path, *r_path;
+static int rtld_used;
+static int ssp_used;
+static int runtime;
+static int ldd_mode;
+static int ldso_fail;
+static jmp_buf rtld_fail;
+static pthread_rwlock_t lock;
+static struct debug debug;
+static size_t *auxv;
+
+struct debug *_dl_debug_addr = &debug;
+
+#define AUX_CNT 24
 #define DYN_CNT 34
 
 static void decode_vec(size_t *v, size_t *a, size_t cnt)
@@ -62,8 +97,17 @@ static void decode_vec(size_t *v, size_t *a, size_t cnt)
 	}
 }
 
-static uint32_t hash(const char *s)
+static int search_vec(size_t *v, size_t *r, size_t key)
+{
+	for (; v[0]!=key; v+=2)
+		if (!v[0]) return 0;
+	*r = v[1];
+	return 1;
+}
+
+static uint32_t sysv_hash(const char *s0)
 {
+	const unsigned char *s = (void *)s0;
 	uint_fast32_t h = 0;
 	while (*s) {
 		h = 16*h + *s++;
@@ -72,9 +116,21 @@ static uint32_t hash(const char *s)
 	return h & 0xfffffff;
 }
 
-static Sym *lookup(const char *s, uint32_t h, Sym *syms, uint32_t *hashtab, char *strings)
+static uint32_t gnu_hash(const char *s0)
+{
+	const unsigned char *s = (void *)s0;
+	uint_fast32_t h = 5381;
+	for (; *s; s++)
+		h = h*33 + *s;
+	return h;
+}
+
+static Sym *sysv_lookup(const char *s, uint32_t h, struct dso *dso)
 {
 	size_t i;
+	Sym *syms = dso->syms;
+	uint32_t *hashtab = dso->hashtab;
+	char *strings = dso->strings;
 	for (i=hashtab[2+h%hashtab[0]]; i; i=hashtab[2+hashtab[0]+i]) {
 		if (!strcmp(s, strings+syms[i].st_name))
 			return syms+i;
@@ -82,22 +138,77 @@ static Sym *lookup(const char *s, uint32_t h, Sym *syms, uint32_t *hashtab, char
 	return 0;
 }
 
+static Sym *gnu_lookup(const char *s, uint32_t h1, struct dso *dso)
+{
+	Sym *sym;
+	char *strings;
+	uint32_t *hashtab = dso->ghashtab;
+	uint32_t nbuckets = hashtab[0];
+	uint32_t *buckets = hashtab + 4 + hashtab[2]*(sizeof(size_t)/4);
+	uint32_t h2;
+	uint32_t *hashval;
+	uint32_t n = buckets[h1 % nbuckets];
+
+	if (!n) return 0;
+
+	strings = dso->strings;
+	sym = dso->syms + n;
+	hashval = buckets + nbuckets + (n - hashtab[1]);
+
+	for (h1 |= 1; ; sym++) {
+		h2 = *hashval++;
+		if ((h1 == (h2|1)) && !strcmp(s, strings + sym->st_name))
+			return sym;
+		if (h2 & 1) break;
+	}
+
+	return 0;
+}
+
 #define OK_TYPES (1<<STT_NOTYPE | 1<<STT_OBJECT | 1<<STT_FUNC | 1<<STT_COMMON)
+#define OK_BINDS (1<<STB_GLOBAL | 1<<STB_WEAK)
 
 static void *find_sym(struct dso *dso, const char *s, int need_def)
 {
-	uint32_t h = hash(s);
+	uint32_t h = 0, gh = 0;
+	void *def = 0;
+	if (dso->ghashtab) {
+		gh = gnu_hash(s);
+		if (gh == 0xf9040207 && !strcmp(s, "dlopen")) rtld_used = 1;
+		if (gh == 0xf4dc4ae && !strcmp(s, "dlsym")) rtld_used = 1;
+		if (gh == 0x1f4039c9 && !strcmp(s, "__stack_chk_fail")) ssp_used = 1;
+	} else {
+		h = sysv_hash(s);
+		if (h == 0x6b366be && !strcmp(s, "dlopen")) rtld_used = 1;
+		if (h == 0x6b3afd && !strcmp(s, "dlsym")) rtld_used = 1;
+		if (h == 0x595a4cc && !strcmp(s, "__stack_chk_fail")) ssp_used = 1;
+	}
 	for (; dso; dso=dso->next) {
-		Sym *sym = lookup(s, h, dso->syms, dso->hashtab, dso->strings);
+		Sym *sym;
+		if (!dso->global) continue;
+		if (dso->ghashtab) {
+			if (!gh) gh = gnu_hash(s);
+			sym = gnu_lookup(s, gh, dso);
+		} else {
+			if (!h) h = sysv_hash(s);
+			sym = sysv_lookup(s, h, dso);
+		}
 		if (sym && (!need_def || sym->st_shndx) && sym->st_value
-		 && (1<<(sym->st_info&0xf) & OK_TYPES))
-			return dso->base + sym->st_value;
+		 && (1<<(sym->st_info&0xf) & OK_TYPES)
+		 && (1<<(sym->st_info>>4) & OK_BINDS)) {
+			if (def && sym->st_info>>4 == STB_WEAK) continue;
+			def = dso->base + sym->st_value;
+			if (sym->st_info>>4 == STB_GLOBAL) break;
+		}
 	}
-	return 0;
+	return def;
 }
 
-static void do_relocs(unsigned char *base, size_t *rel, size_t rel_size, size_t stride, Sym *syms, char *strings, struct dso *dso)
+static void do_relocs(struct dso *dso, size_t *rel, size_t rel_size, size_t stride)
 {
+	unsigned char *base = dso->base;
+	Sym *syms = dso->syms;
+	char *strings = dso->strings;
 	Sym *sym;
 	const char *name;
 	size_t sym_val, sym_size;
@@ -113,17 +224,59 @@ static void do_relocs(unsigned char *base, size_t *rel, size_t rel_size, size_t
 		if (sym_index) {
 			sym = syms + sym_index;
 			name = strings + sym->st_name;
-			ctx = IS_COPY(type) ? dso->next : dso;
-			sym_val = (size_t)find_sym(ctx, name, 1);
+			ctx = IS_COPY(type) ? head->next : head;
+			sym_val = (size_t)find_sym(ctx, name, IS_PLT(type));
+			if (!sym_val && sym->st_info>>4 != STB_WEAK) {
+				snprintf(errbuf, sizeof errbuf,
+					"Error relocating %s: %s: symbol not found",
+					dso->name, name);
+				if (runtime) longjmp(rtld_fail, 1);
+				dprintf(2, "%s\n", errbuf);
+				ldso_fail = 1;
+				continue;
+			}
 			sym_size = sym->st_size;
+		} else {
+			sym_val = sym_size = 0;
 		}
 		do_single_reloc(reloc_addr, type, sym_val, sym_size, base, rel[2]);
 	}
 }
 
+/* A huge hack: to make up for the wastefulness of shared libraries
+ * needing at least a page of dirty memory even if they have no global
+ * data, we reclaim the gaps at the beginning and end of writable maps
+ * and "donate" them to the heap by setting up minimal malloc
+ * structures and then freeing them. */
+
+static void reclaim(unsigned char *base, size_t start, size_t end)
+{
+	size_t *a, *z;
+	start = start + 6*sizeof(size_t)-1 & -4*sizeof(size_t);
+	end = (end & -4*sizeof(size_t)) - 2*sizeof(size_t);
+	if (start>end || end-start < 4*sizeof(size_t)) return;
+	a = (size_t *)(base + start);
+	z = (size_t *)(base + end);
+	a[-2] = 1;
+	a[-1] = z[0] = end-start + 2*sizeof(size_t) | 1;
+	z[1] = 1;
+	free(a);
+}
+
+static void reclaim_gaps(unsigned char *base, Phdr *ph, size_t phent, size_t phcnt)
+{
+	for (; phcnt--; ph=(void *)((char *)ph+phent)) {
+		if (ph->p_type!=PT_LOAD) continue;
+		if ((ph->p_flags&(PF_R|PF_W))!=(PF_R|PF_W)) continue;
+		reclaim(base, ph->p_vaddr & -PAGE_SIZE, ph->p_vaddr);
+		reclaim(base, ph->p_vaddr+ph->p_memsz,
+			ph->p_vaddr+ph->p_memsz+PAGE_SIZE-1 & -PAGE_SIZE);
+	}
+}
+
 static void *map_library(int fd, size_t *lenp, unsigned char **basep, size_t *dynp)
 {
-	size_t buf[896/sizeof(size_t)];
+	Ehdr buf[(896+sizeof(Ehdr))/sizeof(Ehdr)];
 	size_t phsize;
 	size_t addr_min=SIZE_MAX, addr_max=0, map_len;
 	size_t this_min, this_max;
@@ -137,11 +290,11 @@ static void *map_library(int fd, size_t *lenp, unsigned char **basep, size_t *dy
 
 	ssize_t l = read(fd, buf, sizeof buf);
 	if (l<sizeof *eh) return 0;
-	eh = (void *)buf;
+	eh = buf;
 	phsize = eh->e_phentsize * eh->e_phnum;
 	if (phsize + sizeof *eh > l) return 0;
 	if (eh->e_phoff + phsize > l) {
-		l = pread(fd, buf+sizeof *eh, phsize, eh->e_phoff);
+		l = pread(fd, buf+1, phsize, eh->e_phoff);
 		if (l != phsize) return 0;
 		eh->e_phoff = sizeof *eh;
 	}
@@ -171,7 +324,7 @@ static void *map_library(int fd, size_t *lenp, unsigned char **basep, size_t *dy
 	 * the length of the file. This is okay because we will not
 	 * use the invalid part; we just need to reserve the right
 	 * amount of virtual address space to map over later. */
-	map = mmap(0, map_len, prot, MAP_PRIVATE, fd, off_start);
+	map = mmap((void *)addr_min, map_len, prot, MAP_PRIVATE, fd, off_start);
 	if (map==MAP_FAILED) return 0;
 	base = map - addr_min;
 	ph = (void *)((char *)buf + eh->e_phoff);
@@ -185,32 +338,67 @@ static void *map_library(int fd, size_t *lenp, unsigned char **basep, size_t *dy
 		prot = (((ph->p_flags&PF_R) ? PROT_READ : 0) |
 			((ph->p_flags&PF_W) ? PROT_WRITE: 0) |
 			((ph->p_flags&PF_X) ? PROT_EXEC : 0));
-		if (mmap(base+this_min, this_max-this_min, prot, MAP_PRIVATE|MAP_FIXED, fd, off_start) == MAP_FAILED) {
-			munmap(map, map_len);
-			return 0;
-		}
+		if (mmap(base+this_min, this_max-this_min, prot, MAP_PRIVATE|MAP_FIXED, fd, off_start) == MAP_FAILED)
+			goto error;
 		if (ph->p_memsz > ph->p_filesz) {
 			size_t brk = (size_t)base+ph->p_vaddr+ph->p_filesz;
 			size_t pgbrk = brk+PAGE_SIZE-1 & -PAGE_SIZE;
 			memset((void *)brk, 0, pgbrk-brk & PAGE_SIZE-1);
-			if (pgbrk-(size_t)base < this_max && mmap((void *)pgbrk, (size_t)base+this_max-pgbrk, prot, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) == MAP_FAILED) {
-				munmap(map, map_len);
-				return 0;
-			}
+			if (pgbrk-(size_t)base < this_max && mmap((void *)pgbrk, (size_t)base+this_max-pgbrk, prot, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) == MAP_FAILED)
+				goto error;
 		}
 	}
+	for (i=0; ((size_t *)(base+dyn))[i]; i+=2)
+		if (((size_t *)(base+dyn))[i]==DT_TEXTREL) {
+			if (mprotect(map, map_len, PROT_READ|PROT_WRITE|PROT_EXEC) < 0)
+				goto error;
+			break;
+		}
+	if (!runtime) reclaim_gaps(base, (void *)((char *)buf + eh->e_phoff),
+		eh->e_phentsize, eh->e_phnum);
 	*lenp = map_len;
 	*basep = base;
 	*dynp = dyn;
 	return map;
+error:
+	munmap(map, map_len);
+	return 0;
+}
+
+static int path_open(const char *name, const char *search, char *buf, size_t buf_size)
+{
+	const char *s=search, *z;
+	int l, fd;
+	for (;;) {
+		while (*s==':') s++;
+		if (!*s) return -1;
+		z = strchr(s, ':');
+		l = z ? z-s : strlen(s);
+		snprintf(buf, buf_size, "%.*s/%s", l, s, name);
+		if ((fd = open(buf, O_RDONLY))>=0) return fd;
+		s += l;
+	}
+}
+
+static void decode_dyn(struct dso *p)
+{
+	size_t dyn[DYN_CNT] = {0};
+	decode_vec(p->dynv, dyn, DYN_CNT);
+	p->syms = (void *)(p->base + dyn[DT_SYMTAB]);
+	p->strings = (void *)(p->base + dyn[DT_STRTAB]);
+	if (dyn[0]&(1<<DT_HASH))
+		p->hashtab = (void *)(p->base + dyn[DT_HASH]);
+	if (search_vec(p->dynv, dyn, DT_GNU_HASH))
+		p->ghashtab = (void *)(p->base + *dyn);
 }
 
 static struct dso *load_library(const char *name)
 {
+	char buf[2*NAME_MAX+2];
+	const char *pathname;
 	unsigned char *base, *map;
 	size_t dyno, map_len;
 	struct dso *p;
-	size_t dyn[DYN_CNT] = {0};
 	int fd;
 	struct stat st;
 
@@ -226,31 +414,40 @@ static struct dso *load_library(const char *name)
 				if (!libc->prev) {
 					tail->next = libc;
 					libc->prev = tail;
-					tail = libc;
+					tail = libc->next ? libc->next : libc;
 				}
 				return libc;
 			}
 		}
 	}
-	/* Search for the name to see if it's already loaded */
-	for (p=head->next; p; p=p->next) {
-		if (!strcmp(p->name, name)) {
-			p->refcnt++;
-			return p;
-		}
-	}
-	if (name[0] == '/') {
+	if (strchr(name, '/')) {
+		pathname = name;
 		fd = open(name, O_RDONLY);
 	} else {
-		static const char path[] = "/lib/\0/usr/local/lib/\0/usr/lib/\0";
-		const char *s;
-		char buf[NAME_MAX+32];
-		if (strlen(name) > NAME_MAX || strchr(name, '/')) return 0;
-		for (s=path; *s; s+=strlen(s)+1) {
-			strcpy(buf, s);
-			strcat(buf, name);
-			if ((fd = open(buf, O_RDONLY))>=0) break;
+		/* Search for the name to see if it's already loaded */
+		for (p=head->next; p; p=p->next) {
+			if (p->shortname && !strcmp(p->shortname, name)) {
+				p->refcnt++;
+				return p;
+			}
+		}
+		if (strlen(name) > NAME_MAX) return 0;
+		fd = -1;
+		if (r_path) fd = path_open(name, r_path, buf, sizeof buf);
+		if (fd < 0 && env_path) fd = path_open(name, env_path, buf, sizeof buf);
+		if (fd < 0) {
+			if (!sys_path) {
+				FILE *f = fopen(ETC_LDSO_PATH, "r");
+				if (f) {
+					if (getline(&sys_path, (size_t[1]){0}, f) > 0)
+						sys_path[strlen(sys_path)-1]=0;
+					fclose(f);
+				}
+			}
+			if (sys_path) fd = path_open(name, sys_path, buf, sizeof buf);
+			else fd = path_open(name, "/lib:/usr/local/lib:/usr/lib", buf, sizeof buf);
 		}
+		pathname = buf;
 	}
 	if (fd < 0) return 0;
 	if (fstat(fd, &st) < 0) {
@@ -259,6 +456,10 @@ static struct dso *load_library(const char *name)
 	}
 	for (p=head->next; p; p=p->next) {
 		if (p->dev == st.st_dev && p->ino == st.st_ino) {
+			/* If this library was previously loaded with a
+			 * pathname but a search found the same inode,
+			 * setup its shortname so it can be found by name. */
+			if (!p->shortname) p->shortname = strrchr(p->name, '/')+1;
 			close(fd);
 			p->refcnt++;
 			return p;
@@ -267,7 +468,7 @@ static struct dso *load_library(const char *name)
 	map = map_library(fd, &map_len, &base, &dyno);
 	close(fd);
 	if (!map) return 0;
-	p = calloc(1, sizeof *p + strlen(name) + 1);
+	p = calloc(1, sizeof *p + strlen(pathname) + 1);
 	if (!p) {
 		munmap(map, map_len);
 		return 0;
@@ -277,115 +478,448 @@ static struct dso *load_library(const char *name)
 	p->map_len = map_len;
 	p->base = base;
 	p->dynv = (void *)(base + dyno);
-	decode_vec(p->dynv, dyn, DYN_CNT);
+	decode_dyn(p);
 
-	p->syms = (void *)(base + dyn[DT_SYMTAB]);
-	p->hashtab = (void *)(base + dyn[DT_HASH]);
-	p->strings = (void *)(base + dyn[DT_STRTAB]);
 	p->dev = st.st_dev;
 	p->ino = st.st_ino;
-	p->global = 1;
 	p->refcnt = 1;
-	strcpy(p->name, name);
+	p->name = p->buf;
+	strcpy(p->name, pathname);
+	/* Add a shortname only if name arg was not an explicit pathname. */
+	if (pathname != name) p->shortname = strrchr(p->name, '/')+1;
 
 	tail->next = p;
 	p->prev = tail;
 	tail = p;
 
+	if (ldd_mode) dprintf(1, "\t%s => %s (%p)\n", name, pathname, base);
+
 	return p;
 }
 
 static void load_deps(struct dso *p)
 {
-	size_t i;
+	size_t i, ndeps=0;
+	struct dso ***deps = &p->deps, **tmp, *dep;
 	for (; p; p=p->next) {
+		for (i=0; p->dynv[i]; i+=2) {
+			if (p->dynv[i] != DT_RPATH) continue;
+			r_path = (void *)(p->strings + p->dynv[i+1]);
+		}
 		for (i=0; p->dynv[i]; i+=2) {
 			if (p->dynv[i] != DT_NEEDED) continue;
-			load_library(p->strings + p->dynv[i+1]);
+			dep = load_library(p->strings + p->dynv[i+1]);
+			if (!dep) {
+				snprintf(errbuf, sizeof errbuf,
+					"Error loading shared library %s: %m (needed by %s)",
+					p->strings + p->dynv[i+1], p->name);
+				if (runtime) longjmp(rtld_fail, 1);
+				dprintf(2, "%s\n", errbuf);
+				ldso_fail = 1;
+				continue;
+			}
+			if (runtime) {
+				tmp = realloc(*deps, sizeof(*tmp)*(ndeps+2));
+				if (!tmp) longjmp(rtld_fail, 1);
+				tmp[ndeps++] = dep;
+				tmp[ndeps] = 0;
+				*deps = tmp;
+			}
 		}
+		r_path = 0;
+	}
+}
+
+static void load_preload(char *s)
+{
+	int tmp;
+	char *z;
+	for (z=s; *z; s=z) {
+		for (   ; *s && isspace(*s); s++);
+		for (z=s; *z && !isspace(*z); z++);
+		tmp = *z;
+		*z = 0;
+		load_library(s);
+		*z = tmp;
 	}
 }
 
+static void make_global(struct dso *p)
+{
+	for (; p; p=p->next) p->global = 1;
+}
+
 static void reloc_all(struct dso *p)
 {
 	size_t dyn[DYN_CNT] = {0};
 	for (; p; p=p->next) {
 		if (p->relocated) continue;
 		decode_vec(p->dynv, dyn, DYN_CNT);
-		do_relocs(p->base, (void *)(p->base+dyn[DT_JMPREL]), dyn[DT_PLTRELSZ],
-			2+(dyn[DT_PLTREL]==DT_RELA), p->syms, p->strings, p);
-		do_relocs(p->base, (void *)(p->base+dyn[DT_REL]), dyn[DT_RELSZ],
-			2, p->syms, p->strings, p);
-		do_relocs(p->base, (void *)(p->base+dyn[DT_RELA]), dyn[DT_RELASZ],
-			3, p->syms, p->strings, p);
+#ifdef NEED_ARCH_RELOCS
+		do_arch_relocs(p, head);
+#endif
+		do_relocs(p, (void *)(p->base+dyn[DT_JMPREL]), dyn[DT_PLTRELSZ],
+			2+(dyn[DT_PLTREL]==DT_RELA));
+		do_relocs(p, (void *)(p->base+dyn[DT_REL]), dyn[DT_RELSZ], 2);
+		do_relocs(p, (void *)(p->base+dyn[DT_RELA]), dyn[DT_RELASZ], 3);
+		p->relocated = 1;
+	}
+}
+
+static void free_all(struct dso *p)
+{
+	struct dso *n;
+	while (p) {
+		n = p->next;
+		if (p->map) free(p);
+		p = n;
+	}
+}
+
+static size_t find_dyn(Phdr *ph, size_t cnt, size_t stride)
+{
+	for (; cnt--; ph = (void *)((char *)ph + stride))
+		if (ph->p_type == PT_DYNAMIC)
+			return ph->p_vaddr;
+	return 0;
+}
+
+static void do_init_fini(struct dso *p)
+{
+	size_t dyn[DYN_CNT] = {0};
+	for (; p; p=p->prev) {
+		if (p->constructed) return;
+		decode_vec(p->dynv, dyn, DYN_CNT);
+		if (dyn[0] & (1<<DT_FINI))
+			atexit((void (*)(void))(p->base + dyn[DT_FINI]));
+		if (dyn[0] & (1<<DT_INIT))
+			((void (*)(void))(p->base + dyn[DT_INIT]))();
+		p->constructed = 1;
 	}
 }
 
-void *__dynlink(int argc, char **argv, size_t *got)
+void _dl_debug_state(void)
 {
-	size_t *auxv, aux[AUX_CNT] = {0};
-	size_t app_dyn[DYN_CNT] = {0};
-	size_t lib_dyn[DYN_CNT] = {0};
+}
+
+void *__dynlink(int argc, char **argv)
+{
+	size_t aux[AUX_CNT] = {0};
 	size_t i;
 	Phdr *phdr;
-	struct dso lib, app;
+	Ehdr *ehdr;
+	static struct dso builtin_dsos[3];
+	struct dso *const app = builtin_dsos+0;
+	struct dso *const lib = builtin_dsos+1;
+	struct dso *const vdso = builtin_dsos+2;
+	char *env_preload=0;
 
 	/* Find aux vector just past environ[] */
-	for (i=argc+1; argv[i]; i++);
+	for (i=argc+1; argv[i]; i++)
+		if (!memcmp(argv[i], "LD_LIBRARY_PATH=", 16))
+			env_path = argv[i]+16;
+		else if (!memcmp(argv[i], "LD_PRELOAD=", 11))
+			env_preload = argv[i]+11;
 	auxv = (void *)(argv+i+1);
 
 	decode_vec(auxv, aux, AUX_CNT);
 
-	/* Relocate ldso's DYNAMIC pointer and load vector */
-	decode_vec((void *)(got[0] += aux[AT_BASE]), lib_dyn, DYN_CNT);
+	/* Only trust user/env if kernel says we're not suid/sgid */
+	if ((aux[0]&0x7800)!=0x7800 || aux[AT_UID]!=aux[AT_EUID]
+	  || aux[AT_GID]!=aux[AT_EGID] || aux[AT_SECURE]) {
+		env_path = 0;
+		env_preload = 0;
+	}
+
+	/* If the dynamic linker was invoked as a program itself, AT_BASE
+	 * will not be set. In that case, we assume the base address is
+	 * the start of the page containing the PHDRs; I don't know any
+	 * better approach... */
+	if (!aux[AT_BASE]) {
+		aux[AT_BASE] = aux[AT_PHDR] & -PAGE_SIZE;
+		aux[AT_PHDR] = aux[AT_PHENT] = aux[AT_PHNUM] = 0;
+	}
 
-	/* Find the program image's DYNAMIC section and decode it */
-	phdr = (void *)aux[AT_PHDR];
-	for (i=aux[AT_PHNUM]; i--; phdr=(void *)((char *)phdr + aux[AT_PHENT])) {
-		if (phdr->p_type == PT_DYNAMIC) {
-			decode_vec((void *)phdr->p_vaddr, app_dyn, DYN_CNT);
-			break;
+	/* The dynamic linker load address is passed by the kernel
+	 * in the AUX vector, so this is easy. */
+	lib->base = (void *)aux[AT_BASE];
+	lib->name = lib->shortname = "libc.so";
+	lib->global = 1;
+	ehdr = (void *)lib->base;
+	lib->dynv = (void *)(lib->base + find_dyn(
+		(void *)(aux[AT_BASE]+ehdr->e_phoff),
+		ehdr->e_phnum, ehdr->e_phentsize));
+	decode_dyn(lib);
+
+	if (aux[AT_PHDR]) {
+		size_t interp_off = 0;
+		/* Find load address of the main program, via AT_PHDR vs PT_PHDR. */
+		phdr = (void *)aux[AT_PHDR];
+		for (i=aux[AT_PHNUM]; i; i--, phdr=(void *)((char *)phdr + aux[AT_PHENT])) {
+			if (phdr->p_type == PT_PHDR)
+				app->base = (void *)(aux[AT_PHDR] - phdr->p_vaddr);
+			else if (phdr->p_type == PT_INTERP)
+				interp_off = (size_t)phdr->p_vaddr;
+		}
+		if (interp_off) lib->name = (char *)app->base + interp_off;
+		app->name = argv[0];
+		app->dynv = (void *)(app->base + find_dyn(
+			(void *)aux[AT_PHDR], aux[AT_PHNUM], aux[AT_PHENT]));
+	} else {
+		int fd;
+		char *ldname = argv[0];
+		size_t dyno, l = strlen(ldname);
+		if (l >= 3 && !strcmp(ldname+l-3, "ldd")) ldd_mode = 1;
+		*argv++ = (void *)-1;
+		if (argv[0] && !strcmp(argv[0], "--")) *argv++ = (void *)-1;
+		if (!argv[0]) {
+			dprintf(2, "musl libc/dynamic program loader\n");
+			dprintf(2, "usage: %s pathname%s\n", ldname,
+				ldd_mode ? "" : " [args]");
+			_exit(1);
+		}
+		fd = open(argv[0], O_RDONLY);
+		if (fd < 0) {
+			dprintf(2, "%s: cannot load %s: %s\n", ldname, argv[0], strerror(errno));
+			_exit(1);
+		}
+		runtime = 1;
+		ehdr = (void *)map_library(fd, &app->map_len, &app->base, &dyno);
+		if (!ehdr) {
+			dprintf(2, "%s: %s: Not a valid dynamic program\n", ldname, argv[0]);
+			_exit(1);
+		}
+		runtime = 0;
+		close(fd);
+		lib->name = ldname;
+		app->name = argv[0];
+		app->dynv = (void *)(app->base + dyno);
+		aux[AT_ENTRY] = ehdr->e_entry;
+	}
+	app->global = 1;
+	app->constructed = 1;
+	decode_dyn(app);
+
+	/* Attach to vdso, if provided by the kernel */
+	for (i=0; auxv[i]; i+=2) {
+		size_t vdso_base = auxv[i+1];
+		if (auxv[i] != AT_SYSINFO_EHDR) continue;
+		ehdr = (void *)vdso_base;
+		phdr = (void *)(vdso_base + ehdr->e_phoff);
+		for (i=ehdr->e_phnum; i; i--, phdr=(void *)((char *)phdr + ehdr->e_phentsize)) {
+			if (phdr->p_type == PT_DYNAMIC)
+				vdso->dynv = (void *)(vdso_base + phdr->p_offset);
+			if (phdr->p_type == PT_LOAD)
+				vdso->base = (void *)(vdso_base - phdr->p_vaddr + phdr->p_offset);
 		}
+		vdso->name = vdso->shortname = "linux-gate.so.1";
+		vdso->global = 1;
+		decode_dyn(vdso);
+		vdso->prev = lib;
+		lib->next = vdso;
+		break;
 	}
 
-	app = (struct dso){
-		.base = 0,
-		.strings = (void *)(app_dyn[DT_STRTAB]),
-		.hashtab = (void *)(app_dyn[DT_HASH]),
-		.syms = (void *)(app_dyn[DT_SYMTAB]),
-		.dynv = (void *)(phdr->p_vaddr),
-		.next = &lib
-	};
-
-	lib = (struct dso){
-		.base = (void *)aux[AT_BASE],
-		.strings = (void *)(aux[AT_BASE]+lib_dyn[DT_STRTAB]),
-		.hashtab = (void *)(aux[AT_BASE]+lib_dyn[DT_HASH]),
-		.syms = (void *)(aux[AT_BASE]+lib_dyn[DT_SYMTAB]),
-		.dynv = (void *)(got[0]),
-		.relocated = 1
-	};
-
-	/* Relocate the dynamic linker/libc */
-	do_relocs((void *)aux[AT_BASE], (void *)(aux[AT_BASE]+lib_dyn[DT_REL]),
-		lib_dyn[DT_RELSZ], 2, lib.syms, lib.strings, &app);
-	do_relocs((void *)aux[AT_BASE], (void *)(aux[AT_BASE]+lib_dyn[DT_RELA]),
-		lib_dyn[DT_RELASZ], 3, lib.syms, lib.strings, &app);
-
-	/* At this point the standard library is fully functional */
+	/* Initial dso chain consists only of the app. We temporarily
+	 * append the dynamic linker/libc so we can relocate it, then
+	 * restore the initial chain in preparation for loading third
+	 * party libraries (preload/needed). */
+	head = tail = app;
+	libc = lib;
+	app->next = lib;
+	reloc_all(lib);
+	app->next = 0;
+
+	/* PAST THIS POINT, ALL LIBC INTERFACES ARE FULLY USABLE. */
+
+	/* Donate unused parts of app and library mapping to malloc */
+	reclaim_gaps(app->base, (void *)aux[AT_PHDR], aux[AT_PHENT], aux[AT_PHNUM]);
+	ehdr = (void *)lib->base;
+	reclaim_gaps(lib->base, (void *)(lib->base+ehdr->e_phoff),
+		ehdr->e_phentsize, ehdr->e_phnum);
+
+	/* Load preload/needed libraries, add their symbols to the global
+	 * namespace, and perform all remaining relocations. The main
+	 * program must be relocated LAST since it may contain copy
+	 * relocations which depend on libraries' relocations. */
+	if (env_preload) load_preload(env_preload);
+	load_deps(app);
+	make_global(app);
+	reloc_all(app->next);
+	reloc_all(app);
+
+	if (ldso_fail) _exit(127);
+	if (ldd_mode) _exit(0);
+
+	/* Switch to runtime mode: any further failures in the dynamic
+	 * linker are a reportable failure rather than a fatal startup
+	 * error. If the dynamic loader (dlopen) will not be used, free
+	 * all memory used by the dynamic linker. */
+	runtime = 1;
+
+#ifndef DYNAMIC_IS_RO
+	for (i=0; app->dynv[i]; i+=2)
+		if (app->dynv[i]==DT_DEBUG)
+			app->dynv[i+1] = (size_t)&debug;
+#endif
+	debug.ver = 1;
+	debug.bp = _dl_debug_state;
+	debug.head = head;
+	debug.base = lib->base;
+	debug.state = 0;
+	_dl_debug_state();
 
-	/* Only trust user/env if kernel says we're not suid/sgid */
-	trust_env = (aux[0]&0x7800)==0x7800
-		&& aux[AT_UID]==aux[AT_EUID]
-		&& aux[AT_GID]==aux[AT_EGID];
+	if (ssp_used) __init_ssp(auxv);
 
-	head = tail = &app;
-	libc = &lib;
-	app.next = 0;
-	load_deps(head);
+	do_init_fini(tail);
 
-	reloc_all(head);
+	if (!rtld_used) {
+		free_all(head);
+		free(sys_path);
+		reclaim((void *)builtin_dsos, 0, sizeof builtin_dsos);
+	}
 
 	errno = 0;
 	return (void *)aux[AT_ENTRY];
 }
+
+void *dlopen(const char *file, int mode)
+{
+	struct dso *volatile p, *orig_tail = tail, *next;
+	size_t i;
+	int cs;
+
+	if (!file) return head;
+
+	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
+	pthread_rwlock_wrlock(&lock);
+
+	if (setjmp(rtld_fail)) {
+		/* Clean up anything new that was (partially) loaded */
+		if (p->deps) for (i=0; p->deps[i]; i++)
+			if (p->deps[i]->global < 0)
+				p->deps[i]->global = 0;
+		for (p=orig_tail->next; p; p=next) {
+			next = p->next;
+			munmap(p->map, p->map_len);
+			free(p->deps);
+			free(p);
+		}
+		tail = orig_tail;
+		tail->next = 0;
+		p = 0;
+		errflag = 1;
+		goto end;
+	} else p = load_library(file);
+
+	if (!p) {
+		snprintf(errbuf, sizeof errbuf,
+			"Error loading shared library %s: %m", file);
+		errflag = 1;
+		goto end;
+	}
+
+	/* First load handling */
+	if (!p->deps) {
+		load_deps(p);
+		if (p->deps) for (i=0; p->deps[i]; i++)
+			if (!p->deps[i]->global)
+				p->deps[i]->global = -1;
+		if (!p->global) p->global = -1;
+		reloc_all(p);
+		if (p->deps) for (i=0; p->deps[i]; i++)
+			if (p->deps[i]->global < 0)
+				p->deps[i]->global = 0;
+		if (p->global < 0) p->global = 0;
+	}
+
+	if (mode & RTLD_GLOBAL) {
+		if (p->deps) for (i=0; p->deps[i]; i++)
+			p->deps[i]->global = 1;
+		p->global = 1;
+	}
+
+	if (ssp_used) __init_ssp(auxv);
+
+	_dl_debug_state();
+
+	do_init_fini(tail);
+end:
+	pthread_rwlock_unlock(&lock);
+	pthread_setcancelstate(cs, 0);
+	return p;
+}
+
+static void *do_dlsym(struct dso *p, const char *s, void *ra)
+{
+	size_t i;
+	uint32_t h = 0, gh = 0;
+	Sym *sym;
+	if (p == RTLD_NEXT) {
+		for (p=head; p && (unsigned char *)ra-p->map>p->map_len; p=p->next);
+		if (!p) p=head;
+		void *res = find_sym(p->next, s, 0);
+		if (!res) goto failed;
+		return res;
+	}
+	if (p == head || p == RTLD_DEFAULT) {
+		void *res = find_sym(head, s, 0);
+		if (!res) goto failed;
+		return res;
+	}
+	if (p->ghashtab) {
+		gh = gnu_hash(s);
+		sym = gnu_lookup(s, gh, p);
+	} else {
+		h = sysv_hash(s);
+		sym = sysv_lookup(s, h, p);
+	}
+	if (sym && sym->st_value && (1<<(sym->st_info&0xf) & OK_TYPES))
+		return p->base + sym->st_value;
+	if (p->deps) for (i=0; p->deps[i]; i++) {
+		if (p->deps[i]->ghashtab) {
+			if (!gh) gh = gnu_hash(s);
+			sym = gnu_lookup(s, h, p->deps[i]);
+		} else {
+			if (!h) h = sysv_hash(s);
+			sym = sysv_lookup(s, h, p->deps[i]);
+		}
+		if (sym && sym->st_value && (1<<(sym->st_info&0xf) & OK_TYPES))
+			return p->deps[i]->base + sym->st_value;
+	}
+failed:
+	errflag = 1;
+	snprintf(errbuf, sizeof errbuf, "Symbol not found: %s", s);
+	return 0;
+}
+
+void *__dlsym(void *p, const char *s, void *ra)
+{
+	void *res;
+	pthread_rwlock_rdlock(&lock);
+	res = do_dlsym(p, s, ra);
+	pthread_rwlock_unlock(&lock);
+	return res;
+}
+#else
+void *dlopen(const char *file, int mode)
+{
+	return 0;
+}
+void *__dlsym(void *p, const char *s, void *ra)
+{
+	return 0;
+}
+#endif
+
+char *dlerror()
+{
+	if (!errflag) return 0;
+	errflag = 0;
+	return errbuf;
+}
+
+int dlclose(void *p)
+{
+	return 0;
+}