configure options at link time

src/gc/config.d

@@ -7,25 +7,27 @@
 
 module gc.config;
 
-// The default way to confige the GC is by passing command line argument --DRT-gcopt to
+// The default way to configure the GC is by passing command line argument --DRT-gcopt to
 // the executable, use --DRT-gcopt=help for a list of available options.
 //
-// Configuration can be disabled by building this module with version noinitGCFromCommandline
-// and linking it with your executable:
-//      dmd -version=noinitGCFromCommandline main.d /path/to/druntime/src/gc/config.d
+// Configuration via the command line can be disabled by declaring a variable for the
+// linker to pick up before using it's defult from the runtime:
 //
-// If you want to allow configuration by an environment variable DRT_GCOPT aswell, compile
-// gc.config with version initGCFromEnvironment:
-//      dmd -version=initGCFromEnvironment main.d /path/to/druntime/src/gc/config.d
-
-//version = initGCFromEnvironment; // read settings from environment variable DRT_GCOPT
-version(noinitGCFromCommandline) {} else
-version = initGCFromCommandLine; // read settings from command line argument "--DRT-gcopt=options"
-
-version(initGCFromEnvironment)
-    version = configurable;
-version(initGCFromCommandLine)
-    version = configurable;
+//   extern(C) __gshared bool drt_cmdline_enabled = false;
+//
+// Likewise, declare a boolean drt_envvars_enabled to enable configuration via the
+// environment variable DRT_GCOPT:
+//
+//   extern(C) __gshared bool drt_envvars_enabled = true;
+//
+// Setting default configuration properties in the executable can be done by specifying an
+// array of options named drt_args:
+//
+//   extern(C) __gshared string[] drt_args = [ "gcopt=precise=1 profile=1"];
+//
+// Evaluation order of options is drt_args, then environment variables, then command
+// line arguments, i.e. if command line arguments are not disabled, they can override
+// options specified through the environment or embedded in the executable.
 
 import core.stdc.stdlib;
 import core.stdc.stdio;
@@ -35,6 +37,20 @@ import core.vararg;
 
 extern extern(C) string[] rt_args();
 
+// put each variable in its own COMDAT by making them template instances
+template drt_envvars_enabled()
+{
+    pragma(mangle,"drt_envvars_enabled") extern(C) __gshared bool drt_envvars_enabled = false;
+}
+template drt_cmdline_enabled()
+{
+    pragma(mangle,"drt_cmdline_enabled") extern(C) __gshared bool drt_cmdline_enabled = true;
+}
+template drt_args()
+{
+    pragma(mangle,"drt_args") extern(C) __gshared string[] drt_args = [];
+}
+
 struct Config
 {
     bool disable;            // start disabled
@@ -49,14 +65,20 @@ struct Config
 
     bool initialize(...) // avoid inlining
     {
-        version(initGCFromEnvironment)
+        foreach (a; drt_args!())
+        {
+            if(a.length >= 6 && a[0..6] == "gcopt=")
+                if (!parseOptions(a[6 .. $]))
+                    return false;
+        }
+        if(drt_envvars_enabled!())
         {
             auto p = getenv("DRT_GCOPT");
             if (p)
                 if (!parseOptions(p[0 .. strlen(p)]))
                     return false;
         }
-        version(initGCFromCommandLine)
+        if(drt_cmdline_enabled!())
         {
             foreach (a; rt_args)
             {
@@ -68,8 +90,6 @@ struct Config
         return true;
     }
 
-    version (configurable):
-
     string help() @nogc
     {
         return "GC options are specified as white space separated assignments: