mem: Add option to remove shared memory at the end

Add a new option `auto_unlink_shared_backstore` to System so it will
remove the shared backstore used in physical memories when the System is
getting destructed. This will prevent unintended memory leak.

If the shared memory is designed to live through multiple round of
simulations, you may set the option to false to prevent the removal.

Test: Run a simulation with shared_backstore set, and see whether there
    is anything left in /dev/shm/ after simulation ends.
Change-Id: I0267b643bd24e62cb7571674fe98f831c13a586d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/57469
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Daniel Carvalho <odanrc@yahoo.com.br>
Tested-by: kokoro <noreply+kokoro@google.com>

src/mem/physical.cc

@@ -55,6 +55,7 @@
 #include "debug/Checkpoint.hh"
 #include "mem/abstract_mem.hh"
 #include "sim/serialize.hh"
+#include "sim/sim_exit.hh"
 
 /**
  * On Linux, MAP_NORESERVE allow us to simulate a very large memory
@@ -77,10 +78,16 @@ namespace memory
 PhysicalMemory::PhysicalMemory(const std::string& _name,
                                const std::vector<AbstractMemory*>& _memories,
                                bool mmap_using_noreserve,
-                               const std::string& shared_backstore) :
+                               const std::string& shared_backstore,
+                               bool auto_unlink_shared_backstore) :
     _name(_name), size(0), mmapUsingNoReserve(mmap_using_noreserve),
     sharedBackstore(shared_backstore), sharedBackstoreSize(0)
 {
+    // Register cleanup callback if requested.
+    if (auto_unlink_shared_backstore && !sharedBackstore.empty()) {
+        registerExitCallback([=]() { shm_unlink(shared_backstore.c_str()); });
+    }
+
     if (mmap_using_noreserve)
         warn("Not reserving swap space. May cause SIGSEGV on actual usage\n");
 

src/mem/physical.hh

@@ -174,7 +174,8 @@ class PhysicalMemory : public Serializable
     PhysicalMemory(const std::string& _name,
                    const std::vector<AbstractMemory*>& _memories,
                    bool mmap_using_noreserve,
-                   const std::string& shared_backstore);
+                   const std::string& shared_backstore,
+                   bool auto_unlink_shared_backstore);
 
     /**
      * Unmap all the backing store we have used.

src/sim/System.py

@@ -87,6 +87,9 @@ class System(SimObject):
     shared_backstore = Param.String("", "backstore's shmem segment filename, "
         "use to directly address the backstore from another host-OS process. "
         "Leave this empty to unset the MAP_SHARED flag.")
+    auto_unlink_shared_backstore = Param.Bool(False, "Automatically remove the "
+        "shmem segment file upon destruction. This is used only if "
+        "shared_backstore is non-empty.")
 
     cache_line_size = Param.Unsigned(64, "Cache line size in bytes")
 

src/sim/system.cc

@@ -182,7 +182,7 @@ System::System(const Params &p)
       physProxy(_systemPort, p.cache_line_size),
       workload(p.workload),
       physmem(name() + ".physmem", p.memories, p.mmap_using_noreserve,
-              p.shared_backstore),
+              p.shared_backstore, p.auto_unlink_shared_backstore),
       ShadowRomRanges(p.shadow_rom_ranges.begin(),
                       p.shadow_rom_ranges.end()),
       memoryMode(p.mem_mode),