PNaCl Dynamic Linking: Using unordered_set to disallow duplicate modules.

src/untrusted/pll_loader/pll_loader.cc

Index: src/untrusted/pll_loader/pll_loader.cc
diff --git a/src/untrusted/pll_loader/pll_loader.cc b/src/untrusted/pll_loader/pll_loader.cc
index aa7724e0c02ae42149d6f13dbdb39152ac9a2116..4c47665817c49043baffb9202af4f0e2c711dead 100644
--- a/src/untrusted/pll_loader/pll_loader.cc
+++ b/src/untrusted/pll_loader/pll_loader.cc
@@ -6,6 +6,7 @@
 
 #include <stdlib.h>
 #include <string.h>
+#include <sys/stat.h>
 
 #include <algorithm>
 
@@ -84,6 +85,33 @@ void *PLLModule::InstantiateTLSBlock() {
   return base;
 }
 
+void ModuleSet::SetSonameSearchPaths(const std::vector<std::string> &dir_list) {
+  search_paths_ = dir_list;
+}
+
+void ModuleSet::AddBySoname(const char *soname) {
+  // TODO(smklein): Deduplicate rather than failing once dependencies are added.
+  if (sonames_.count(soname) != 0) {
+    NaClLog(LOG_FATAL, "PLL Loader found duplicate soname: %s\n", soname);
+  }
+  sonames_.insert(soname);
+
+  // Actually load the module implied by the soname.
+  struct stat buf;

[Mark Seaborn, 2016/03/26 00:30:10]

Nit: putting this immediately before the stat() call is more idiomatic (i.e. put
var definitions as closer as possible to their uses), and just as efficient.

[Sean Klein, 2016/03/26 00:47:25]

Done.

+  for (auto path : search_paths_) {
+    // Appending "/" might be unnecessary, but "foo/bar" and "foo//bar" should
+    // point to the same file.
+    path.append("/");
+    path.append(soname);
+    if (stat(path.c_str(), &buf) == 0) {
+      AddByFilename(path.c_str());
+      return;
+    }
+  }
+
+  NaClLog(LOG_FATAL, "PLL Loader cannot find shared object file: %s\n", soname);
+}
+
 void ModuleSet::AddByFilename(const char *filename) {
   void *pso_root;
   int err = pnacl_load_elf_file(filename, &pso_root);