[import] Fix segfault on exit in import line trace test

pymtl3/passes/backends/verilog/import_/VerilogVerilatorImportConfigs.py

@@ -130,7 +130,7 @@ class VerilogVerilatorImportConfigs( BasePassConfigs ):
 
     # We enforce the GNU makefile implicit rule that `LDLIBS` should only
     # include library linker flags/names such as `-lfoo`.
-    "ld_libs" : "",
+    "ld_libs" : "-lpthread",
 
     "c_flags" : "",
   }
@@ -269,6 +269,7 @@ def create_vl_cmd( s ):
     opt_level   = "-O3"
     loop_unroll = "--unroll-count 1000000"
     stmt_unroll = "--unroll-stmts 1000000"
+    thread      = "--threads 1"
     trace       = "--trace" if s.vl_trace else ""
     coverage    = "--coverage" if s.vl_coverage else ""
     line_cov    = "--coverage-line" if s.vl_line_coverage else ""
@@ -278,7 +279,7 @@ def create_vl_cmd( s ):
     all_opts = [
       top_module, mk_dir, include, en_assert, opt_level, loop_unroll,
       # stmt_unroll, trace, warnings, flist, src, coverage,
-      stmt_unroll, trace, warnings, src, vlibs, coverage,
+      stmt_unroll, thread, trace, warnings, src, vlibs, coverage,
       line_cov, toggle_cov,
     ]
 
@@ -325,6 +326,8 @@ def create_cc_cmd( s ):
     if not s.is_default("c_flags"):
       c_flags += f" {expand(s.c_flags)}"
 
+    c_flags += f" -std=c++11 -pthread -DVL_TIME_CONTEXT"
+
     c_include_path = " ".join("-I"+p for p in s._get_all_includes() if p)
     out_file = s.get_shared_lib_path()
     c_src_files = " ".join(s._get_c_src_files())
@@ -334,7 +337,17 @@ def create_cc_cmd( s ):
                                   s.vl_line_coverage or \
                                   s.vl_toggle_coverage else ""
 
-    # PP: try not to introduce GNU unique symbols to the shared library.
+    # PP: eliminate GNU unique symbols in the compiled shared library.
+    # See https://stackoverflow.com/a/76664985
+    # ^ this says if a shared library has UNIQUE symbols in it a dlclose
+    # may become a no-op. The solution is to mark all symbols as `hidden`
+    # except for those we want to access in the C wrapper. Note that I've
+    # tried adding the g++ flag `-fvisibility=hidden` and 
+    # __attribute__((visibility("default"))) to APIs, but the compiled
+    # shared library still contains UNIQUE symbols:
+    # % readelf -sW --dyn-syms libVRegTrace_noparam_v.so | grep '\bUNIQUE\b'
+    # The solution proposed in the above post is to use a linker version
+    # script which specifies visibility of all symbols.
     linker_version_script_filename = "verilator_import_linker_version_script.lds"
     dir_to_version_script = os.path.abspath(os.path.dirname(__file__))
     ld_flags += f" -Wl,--version-script={os.path.join(dir_to_version_script, linker_version_script_filename)}"
@@ -460,7 +473,7 @@ def _compile_vl_srcs_from_vl_class_mk( s, all_lines, path, label ):
     cxx_includes = " ".join(map(lambda x: "-I"+x, s._get_all_includes()))
     for src in srcs:
       file_path, obj_name = src
-      cxx_cmd = f"g++ {cxx_includes} -O1 -fPIC -c -o {obj_name}.o {file_path}"
+      cxx_cmd = f"g++ {cxx_includes} -std=c++11 -DVL_TIME_CONTEXT -O1 -fPIC -pthread -lpthread -c -o {obj_name}.o {file_path}"
       if os.path.exists(f"{obj_name}.o"):
         s.vprint(f"Skip compiling {obj_name}.o because it already exists.")
       else:

pymtl3/passes/backends/verilog/import_/test/ImportedObject_test.py

@@ -467,7 +467,25 @@ def construct( s ):
   # 0xFFFFFFFF unsigned
   assert a.line_trace() == 'q = 4294967295'
   a.sim_tick()
-  a.finalize()
+
+  # PP: This is a workaround to the $sformat issue I was seeing with Verilator
+  # 5.016. If I enable this finalize below, the C library will segfault after
+  # all pytest tests have finished. Digging deeper I found this could be
+  # reliably eliminated/reproduced by removing/adding the `thread_local`
+  # specifier to the temporary string used in VL_SFORMAT_X (verilated.h). Note
+  # that the program finishes just fine when this thread-local string is never
+  # used (VL_SFORMAT_X is never invoked). My theory is this could be a
+  # double-free situation: somehow the dynamically allocated memory that
+  # belongs to this thread-local string gets deleted twice: once when we unload
+  # the dynamic library (through a.finalize()) and once at the end of program
+  # execution.
+  #
+  # One stackoverflow post suggests this might be a compiler bug:
+  # https://stackoverflow.com/a/58366171
+  # I tried recompiling with the latest g++ on BRG server (scl-11) but the
+  # segfault persists.
+
+  # a.finalize()
 
 def test_reg_infer_external_trace( do_test ):
   # Test Verilog line trace
@@ -498,7 +516,7 @@ def construct( s ):
   # 0xFFFFFFFF unsigned
   assert a.line_trace() == 'q = 4294967295'
   a.sim_tick()
-  a.finalize()
+  # a.finalize()
 
 def test_incr_on_demand_vcd( do_test ):
   class VIncr( Component, VerilogPlaceholder ):

pymtl3/passes/backends/verilog/import_/verilator_wrapper_c_template.py

@@ -201,6 +201,7 @@
 void seq_eval( V{component_name}_t * m ) {{
 
   V{vl_component_name} * model = (V{vl_component_name} *) m->model;
+  VerilatedContext * context_ptr = m->context_ptr;
 
   // evaluate one time cycle
 
@@ -248,6 +249,7 @@
   #endif
 
   model->eval();
+  context_ptr->timeInc(1);
 
   #if DUMP_VCD
   if ( m->_vcd_en && (ON_DEMAND_VCD_ENABLE || !ON_DEMAND_DUMP_VCD) ) {{