Fixed support for RTLD_NEXT in dlsym()

The previous implementation of this flag was broken--it behaved identically
to RTLD_DEFAULT.  This adds a proper implementation, which examines the address
of the calling function, and uses it to determine which library to use to begin
the symbol search process.

Change-Id: I2ad2b46363f68932af63a3828a22f9c7987eea67

3 files changed, 15 insertions, 5 deletions

diff --git a/linker/dlfcn.c b/linker/dlfcn.c
index dcadce5..30f5f4c 100644
--- a/linker/dlfcn.c
+++ b/linker/dlfcn.c
@@ -90,9 +90,15 @@ void *dlsym(void *handle, const char *symbol)
     }
 
     if(handle == RTLD_DEFAULT) {
-        sym = lookup(symbol, &found);
+        sym = lookup(symbol, &found, NULL);
     } else if(handle == RTLD_NEXT) {
-        sym = lookup(symbol, &found);
+        void *ret_addr = __builtin_return_address(0);
+        soinfo *si = find_containing_library(ret_addr);
+
+        sym = NULL;
+        if(si && si->next) {
+            sym = lookup(symbol, &found, si->next);
+        }
     } else {
         found = (soinfo*)handle;
         sym = lookup_in_library(found, symbol);
diff --git a/linker/linker.c b/linker/linker.c
index 87fb19b..451e96c 100644
--- a/linker/linker.c
+++ b/linker/linker.c
@@ -512,13 +512,17 @@ Elf32_Sym *lookup_in_library(soinfo *si, const char *name)
 
 /* This is used by dl_sym().  It performs a global symbol lookup.
  */
-Elf32_Sym *lookup(const char *name, soinfo **found)
+Elf32_Sym *lookup(const char *name, soinfo **found, soinfo *start)
 {
     unsigned elf_hash = 0;
     Elf32_Sym *s = NULL;
     soinfo *si;
 
-    for(si = solist; (s == NULL) && (si != NULL); si = si->next)
+    if(start == NULL) {
+        start = solist;
+    }
+
+    for(si = start; (s == NULL) && (si != NULL); si = si->next)
     {
         if(si->flags & FLAG_ERROR)
             continue;
diff --git a/linker/linker.h b/linker/linker.h
index 8cd56b0..68ac275 100644
--- a/linker/linker.h
+++ b/linker/linker.h
@@ -224,7 +224,7 @@ extern soinfo libdl_info;
 soinfo *find_library(const char *name);
 unsigned unload_library(soinfo *si);
 Elf32_Sym *lookup_in_library(soinfo *si, const char *name);
-Elf32_Sym *lookup(const char *name, soinfo **found);
+Elf32_Sym *lookup(const char *name, soinfo **found, soinfo *start);
 soinfo *find_containing_library(void *addr);
 Elf32_Sym *find_containing_symbol(void *addr, soinfo *si);
 const char *linker_get_error(void);