dladdr support for dynamic linker (nonstandard extension)

based on patches submitted by boris brezillon. this commit also fixes
the issue whereby the main application and libc don't have the address
ranges of their mappings stored, which was theoretically a problem for
RTLD_NEXT support in dlsym; it didn't actually matter because libc
never calls dlsym, and it seemed to be doing the right thing (by
chance) for symbols in the main program as well.

include/dlfcn.h

@@ -18,6 +18,16 @@ char  *dlerror(void);
 void  *dlopen(const char *, int);
 void  *dlsym(void *, const char *);
 
+#ifdef _GNU_SOURCE
+typedef struct {
+	const char *dli_fname;
+	void *dli_fbase;
+	const char *dli_sname;
+	void *dli_saddr;
+} Dl_info;
+int dladdr(void *, Dl_info *);
+#endif
+
 #ifdef __cplusplus
 }
 #endif

src/ldso/dladdr.c

+#define _GNU_SOURCE
+#include <dlfcn.h>
+
+int __dladdr(void *, Dl_info *);
+
+int dladdr(void *addr, Dl_info *info)
+{
+	return __dladdr(addr, info);
+}

src/ldso/dynlink.c

+#define _GNU_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -584,6 +585,22 @@ static size_t find_dyn(Phdr *ph, size_t cnt, size_t stride)
 	return 0;
 }
 
+static void find_map_range(Phdr *ph, size_t cnt, size_t stride, struct dso *p)
+{
+	size_t min_addr = -1, max_addr = 0;
+	for (; cnt--; ph = (void *)((char *)ph + stride)) {
+		if (ph->p_type != PT_LOAD) continue;
+		if (ph->p_vaddr < min_addr)
+			min_addr = ph->p_vaddr;
+		if (ph->p_vaddr+ph->p_memsz > max_addr)
+			max_addr = ph->p_vaddr+ph->p_memsz;
+	}
+	min_addr &= -PAGE_SIZE;
+	max_addr = (max_addr + PAGE_SIZE-1) & -PAGE_SIZE;
+	p->map = p->base + min_addr;
+	p->map_len = max_addr - min_addr;
+}
+
 static void do_init_fini(struct dso *p)
 {
 	size_t dyn[DYN_CNT] = {0};
@@ -647,6 +664,8 @@ void *__dynlink(int argc, char **argv)
 	lib->name = lib->shortname = "libc.so";
 	lib->global = 1;
 	ehdr = (void *)lib->base;
+	find_map_range((void *)(aux[AT_BASE]+ehdr->e_phoff),
+		ehdr->e_phnum, ehdr->e_phentsize, lib);
 	lib->dynv = (void *)(lib->base + find_dyn(
 		(void *)(aux[AT_BASE]+ehdr->e_phoff),
 		ehdr->e_phnum, ehdr->e_phentsize));
@@ -666,6 +685,8 @@ void *__dynlink(int argc, char **argv)
 		app->name = argv[0];
 		app->dynv = (void *)(app->base + find_dyn(
 			(void *)aux[AT_PHDR], aux[AT_PHNUM], aux[AT_PHENT]));
+		find_map_range((void *)aux[AT_PHDR],
+			aux[AT_PHNUM], aux[AT_PHENT], app);
 	} else {
 		int fd;
 		char *ldname = argv[0];
@@ -891,6 +912,67 @@ failed:
 	return 0;
 }
 
+int __dladdr(void *addr, Dl_info *info)
+{
+	struct dso *p;
+	Sym *sym;
+	uint32_t nsym;
+	char *strings;
+	size_t i;
+	void *best = 0;
+	char *bestname;
+
+	pthread_rwlock_rdlock(&lock);
+	for (p=head; p && (unsigned char *)addr-p->map>p->map_len; p=p->next);
+	pthread_rwlock_unlock(&lock);
+
+	if (!p) return 0;
+
+	sym = p->syms;
+	strings = p->strings;
+	if (p->hashtab) {
+		nsym = p->hashtab[1];
+	} else {
+		uint32_t *buckets;
+		uint32_t *hashval;
+		buckets = p->ghashtab + 4 + (p->ghashtab[2]*sizeof(size_t)/4);
+		sym += p->ghashtab[1];
+		for (i = 0; i < p->ghashtab[0]; i++) {
+			if (buckets[i] > nsym)
+				nsym = buckets[i];
+		}
+		if (nsym) {
+			nsym -= p->ghashtab[1];
+			hashval = buckets + p->ghashtab[0] + nsym;
+			do nsym++;
+			while (!(*hashval++ & 1));
+		}
+	}
+
+	for (; nsym; nsym--, sym++) {
+		if (sym->st_shndx && sym->st_value
+		 && (1<<(sym->st_info&0xf) & OK_TYPES)
+		 && (1<<(sym->st_info>>4) & OK_BINDS)) {
+			void *symaddr = p->base + sym->st_value;
+			if (symaddr > addr || symaddr < best)
+				continue;
+			best = symaddr;
+			bestname = strings + sym->st_name;
+			if (addr == symaddr)
+				break;
+		}
+	}
+
+	if (!best) return 0;
+
+	info->dli_fname = p->name;
+	info->dli_fbase = p->base;
+	info->dli_sname = bestname;
+	info->dli_saddr = best;
+
+	return 1;
+}
+
 void *__dlsym(void *p, const char *s, void *ra)
 {
 	void *res;
@@ -908,6 +990,10 @@ void *__dlsym(void *p, const char *s, void *ra)
 {
 	return 0;
 }
+int __dladdr (void *addr, Dl_info *info)
+{
+	return 0;
+}
 #endif
 
 char *dlerror()