i#4014 dr$sim phys: Avoid malloc in physaddr_t

Switches from std::unordered_map in physaddr_t to a drcontainers
hashtable to avoid malloc and make things safe for statically-linked
drmemtrace.

Similarly, switches from std::ostringstream to dr_snprintf in
physaddr_t::init() to avoid malloc.

Tested on a multi-threaded app which hits the post-init malloc warning
without both fixes (test will be added in a forthcoming PR: it cannot
be added now as physaddr_t is not thread-safe yet).

Issue: #4014

clients/drcachesim/tracer/physaddr.cpp

@@ -1,5 +1,5 @@
 /* **********************************************************
- * Copyright (c) 2015-2020 Google, Inc.  All rights reserved.
+ * Copyright (c) 2015-2022 Google, Inc.  All rights reserved.
  * **********************************************************/
 
 /*
@@ -73,18 +73,29 @@ physaddr_t::physaddr_t()
     // No destructor needed either: ifstream closes when destroyed.
 }
 
+physaddr_t::~physaddr_t()
+{
+    hashtable_delete(&v2p_);
+}
+
 bool
 physaddr_t::init()
 {
 #ifdef LINUX
-    std::ostringstream oss;
-    std::string pagemap =
-        dynamic_cast<std::ostringstream &>(oss << "/proc/" << getpid() << "/pagemap")
-            .str();
+    // Some threads may not do much, so start out small.
+    constexpr int V2P_INITIAL_BITS = 9;
+    hashtable_init_ex(&v2p_, V2P_INITIAL_BITS, HASH_INTPTR, /*strdup=*/false,
+                      /*synch=*/false, nullptr, nullptr, nullptr);
+
+    // We avoid std::ostringstream to avoid malloc use for static linking.
+    constexpr int MAX_PAGEMAP_FNAME = 64;
+    char fname[MAX_PAGEMAP_FNAME];
+    dr_snprintf(fname, sizeof(fname), "/proc/%d/pagemap", getpid());
+    fname[MAX_PAGEMAP_FNAME - 1] = '\0';
     // We can't read pagemap with any buffered i/o, like ifstream, as we'll
     // get EINVAL on any non-8-aligned size, and ifstream at least likes to
     // read buffers of non-aligned sizes.
-    fd_ = open(pagemap.c_str(), O_RDONLY);
+    fd_ = open(fname, O_RDONLY);
     // Accessing /proc/pid/pagemap requires privileges on some distributions,
     // such as Fedora with recent kernels.  We have no choice but to fail there.
     return (fd_ != -1);
@@ -105,7 +116,7 @@ physaddr_t::virtual2physical(addr_t virt)
         // Flush the cache and re-sync with the kernel
         use_cache = false;
         last_vpage_ = PAGE_INVALID;
-        v2p_.clear();
+        hashtable_clear(&v2p_);
         count_ = 0;
     }
     if (use_cache) {
@@ -115,10 +126,14 @@ physaddr_t::virtual2physical(addr_t virt)
             return last_ppage_ + PAGE_OFFS(virt);
         // XXX i#1703: add (debug-build-only) internal stats here and
         // on cache_t::request() fastpath.
-        std::unordered_map<addr_t, addr_t>::iterator exists = v2p_.find(vpage);
-        if (exists != v2p_.end()) {
+        void *lookup = hashtable_lookup(&v2p_, reinterpret_cast<void *>(vpage));
+        if (lookup != nullptr) {
+            addr_t ppage = reinterpret_cast<addr_t>(lookup);
+            // Restore a 0 payload.
+            if (ppage == 1)
+                ppage = 0;
             last_vpage_ = vpage;
-            last_ppage_ = exists->second;
+            last_ppage_ = ppage;
             return last_ppage_ + PAGE_OFFS(virt);
         }
     }
@@ -142,7 +157,9 @@ physaddr_t::virtual2physical(addr_t virt)
         std::cerr << "virtual " << virt << " => physical "
                   << (last_ppage_ + PAGE_OFFS(virt)) << std::endl;
     }
-    v2p_[vpage] = last_ppage_;
+    // Store 0 as 1 since 0 means no entry.
+    hashtable_add(&v2p_, reinterpret_cast<void *>(vpage),
+                  reinterpret_cast<void *>(last_ppage_ == 0 ? 1 : last_ppage_));
     last_vpage_ = vpage;
     return last_ppage_ + PAGE_OFFS(virt);
 #else

clients/drcachesim/tracer/physaddr.h

@@ -1,5 +1,5 @@
 /* **********************************************************
- * Copyright (c) 2015-2020 Google, Inc.  All rights reserved.
+ * Copyright (c) 2015-2022 Google, Inc.  All rights reserved.
  * **********************************************************/
 
 /*
@@ -38,11 +38,14 @@
 
 #include <fstream>
 #include <unordered_map>
+#include "dr_api.h"
+#include "hashtable.h"
 #include "../common/trace_entry.h"
 
 class physaddr_t {
 public:
     physaddr_t();
+    ~physaddr_t();
     bool
     init();
     addr_t
@@ -54,7 +57,9 @@ class physaddr_t {
     addr_t last_vpage_;
     addr_t last_ppage_;
     int fd_;
-    std::unordered_map<addr_t, addr_t> v2p_;
+    // We would use std::unordered_map, but that is not compatible with
+    // statically linking drmemtrace into an app.
+    hashtable_t v2p_;
     unsigned int count_;
 #endif
 };

clients/drcachesim/tracer/tracer.cpp

@@ -3116,14 +3116,6 @@ drmemtrace_client_main(client_id_t id, int argc, const char *argv[])
         have_phys = physaddr.init();
         if (!have_phys)
             NOTIFY(0, "Unable to open pagemap: using virtual addresses.\n");
-        /* Unfortunately the use of std::unordered_map in physaddr_t calls malloc
-         * and thus we cannot support it for static linking, so we override the
-         * DR_DISALLOW_UNSAFE_STATIC declaration.
-         */
-        dr_allow_unsafe_static_behavior();
-#ifdef DRMEMTRACE_STATIC
-        NOTIFY(0, "-use_physical is unsafe with statically linked clients\n");
-#endif
     }
 #ifdef HAS_SNAPPY
     if (op_offline.get_value() && snappy_enabled()) {