systemc: Get sc_main to work even when dynamically linked.

Unfortunately multiply defined weak symbols don't work like they're
supposed to when the different versions are across dynamic linking
boundaries.

Fortunately, a weak symbol with no definition at all will still
consistently evaluate as 0, and a singularly defined weak symbol will
still resolve correctly.

Instead of relying on a weak version of sc_main being overridden by a
strong/non-default definition, this change leaves it as undefined and
detects at run time whether the symbol resolves to 0 or to an actual
code location.

Change-Id: I31c4ff769b0c52277c6cf4845ca3f85000009583
Reviewed-on: https://gem5-review.googlesource.com/11610
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

1 files changed, 8 insertions, 11 deletions

diff --git a/src/systemc/core/sc_main.cc b/src/systemc/core/sc_main.cc
index 2ca5ed494..fec3faeb0 100644
--- a/src/systemc/core/sc_main.cc
+++ b/src/systemc/core/sc_main.cc
@@ -38,16 +38,8 @@
 #include "systemc/ext/core/sc_main.hh"
 #include "systemc/ext/utils/sc_report_handler.hh"
 
-// A default version of this function in case one isn't otherwise defined.
-// This ensures everything will link properly whether or not the user defined
-// a custom sc_main function. If they didn't but still try to call it, throw
-// an error and die.
-[[gnu::weak]] int
-sc_main(int argc, char *argv[])
-{
-    // If python attempts to call sc_main but no sc_main was defined...
-    fatal("sc_main called but not defined.\n");
-}
+// A weak symbol to detect if sc_main has been defined, and if so where it is.
+[[gnu::weak]] int sc_main(int argc, char *argv[]);
 
 namespace sc_core
 {
@@ -65,7 +57,12 @@ class ScMainFiber : public Fiber
     void
     main()
     {
-        ::sc_main(_argc, _argv);
+        if (::sc_main) {
+            ::sc_main(_argc, _argv);
+        } else {
+            // If python tries to call sc_main but no sc_main was defined...
+            fatal("sc_main called but not defined.\n");
+        }
     }
 };