Minimize calls to mprotect
Implement refcounter based data protection guard
to avoid unnecessary calls to mprotect when dlopen/dlclose
is called from a constructor.
Bug: 19124318
Big: 7941716
Change-Id: Id221b84ce75443094f99756dc9950b0a1dc87222
diff --git a/linker/linker.cpp b/linker/linker.cpp
index df8e52e..f7bcd27 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -262,11 +262,6 @@
g_soinfo_links_allocator.free(entry);
}
-static void protect_data(int protection) {
- g_soinfo_allocator.protect_all(protection);
- g_soinfo_links_allocator.protect_all(protection);
-}
-
static soinfo* soinfo_alloc(const char* name, struct stat* file_stat, off64_t file_offset, uint32_t rtld_flags) {
if (strlen(name) >= SOINFO_NAME_LEN) {
DL_ERR("library name \"%s\" too long", name);
@@ -589,6 +584,34 @@
return s;
}
+class ProtectedDataGuard {
+ public:
+ ProtectedDataGuard() {
+ if (ref_count_++ == 0) {
+ protect_data(PROT_READ | PROT_WRITE);
+ }
+ }
+
+ ~ProtectedDataGuard() {
+ if (ref_count_ == 0) { // overflow
+ __libc_fatal("Too many nested calls to dlopen()");
+ }
+
+ if (--ref_count_ == 0) {
+ protect_data(PROT_READ);
+ }
+ }
+ private:
+ void protect_data(int protection) {
+ g_soinfo_allocator.protect_all(protection);
+ g_soinfo_links_allocator.protect_all(protection);
+ }
+
+ static size_t ref_count_;
+};
+
+size_t ProtectedDataGuard::ref_count_ = 0;
+
// Each size has it's own allocator.
template<size_t size>
class SizeBasedAllocator {
@@ -1237,19 +1260,18 @@
return nullptr;
}
}
- protect_data(PROT_READ | PROT_WRITE);
+
+ ProtectedDataGuard guard;
soinfo* si = find_library(name, flags, extinfo);
if (si != nullptr) {
si->call_constructors();
}
- protect_data(PROT_READ);
return si;
}
void do_dlclose(soinfo* si) {
- protect_data(PROT_READ | PROT_WRITE);
+ ProtectedDataGuard guard;
soinfo_unload(si);
- protect_data(PROT_READ);
}
static ElfW(Addr) call_ifunc_resolver(ElfW(Addr) resolver_addr) {
@@ -1595,10 +1617,6 @@
TRACE("[ Calling %s @ %p for '%s' ]", function_name, function, name);
function();
TRACE("[ Done calling %s @ %p for '%s' ]", function_name, function, name);
-
- // The function may have called dlopen(3) or dlclose(3), so we need to ensure our data structures
- // are still writable. This happens with our debug malloc (see http://b/7941716).
- protect_data(PROT_READ | PROT_WRITE);
}
void soinfo::call_pre_init_constructors() {
@@ -2522,15 +2540,19 @@
add_vdso(args);
- si->call_pre_init_constructors();
+ {
+ ProtectedDataGuard guard;
- /* After the prelink_image, the si->load_bias is initialized.
- * For so lib, the map->l_addr will be updated in notify_gdb_of_load.
- * We need to update this value for so exe here. So Unwind_Backtrace
- * for some arch like x86 could work correctly within so exe.
- */
- map->l_addr = si->load_bias;
- si->call_constructors();
+ si->call_pre_init_constructors();
+
+ /* After the prelink_image, the si->load_bias is initialized.
+ * For so lib, the map->l_addr will be updated in notify_gdb_of_load.
+ * We need to update this value for so exe here. So Unwind_Backtrace
+ * for some arch like x86 could work correctly within so exe.
+ */
+ map->l_addr = si->load_bias;
+ si->call_constructors();
+ }
#if TIMING
gettimeofday(&t1, nullptr);
@@ -2673,8 +2695,6 @@
args.abort_message_ptr = &g_abort_message;
ElfW(Addr) start_address = __linker_init_post_relocation(args, linker_addr);
- protect_data(PROT_READ);
-
INFO("[ jumping to _start ]");
// Return the address that the calling assembly stub should jump to.