[svsim] Use -no_save instead of ASLR workarounds (#4845)

For the internal installation of VCS and RHEL, our simulations do not work
due to VCS' save/restore functionality which will launch a simulation,
detect if ASLR is present, and then kill the simulation and relaunch it
with ASLR disabled.  The workaround employed here has been empirically
shown to be problematic for at least one user (#4837).  Drop the ASLR
workaround and add the runtime option `-no_save` which turns off VCS
save/restore functionality.  svsim doesn't support this and it's ill
advised to use non-standard workarounds.

Signed-off-by: Schuyler Eldridge <[email protected]>

Author: seldridge

svsim/src/main/resources/simulation-driver.cpp

@@ -37,10 +37,6 @@
 #include <strings.h>
 #include <unistd.h>
 
-#ifdef SVSIM_BACKEND_ENGAGES_IN_ASLR_SHENANIGANS
-#include <sys/personality.h>
-#endif
-
 #ifdef SVSIM_ENABLE_VERILATOR_SUPPORT
 #include "verilated-sources/VsvsimTestbench__Dpi.h"
 #define DPI_TASK_RETURN_TYPE int
@@ -188,8 +184,6 @@ static struct {
 
   const char *simulationTraceFilepath = NULL;
 
-  bool aslrShenanigansDetected = false;
-
   // Track any outstanding commands that are executing while `run_simulation` is
   // called.  This will be cleared by `simulation_final` before termination.
   //
@@ -862,10 +856,6 @@ static bool processCommand() {
 }
 
 DPI_TASK_RETURN_TYPE simulation_body() {
-  if (state.aslrShenanigansDetected) {
-    failWithError("Backend did not relaunch the executable with ASLR disabled "
-                  "as expected.");
-  }
   /// If we have made it to `simulation_body`, there were no errors on startup
   /// and the first thing we do is send a READY message.
   sendReady();
@@ -930,16 +920,6 @@ DPI_TASK_RETURN_TYPE simulation_final() {
 
 int main(int argc, const char *argv[]) {
 
-#ifdef SVSIM_BACKEND_ENGAGES_IN_ASLR_SHENANIGANS
-  if (!(personality(0xffffffff) & ADDR_NO_RANDOMIZE)) {
-    // See note in `Workspace.scala` on
-    // SVSIM_BACKEND_ENGAGES_IN_ASLR_SHENANIGANS
-    state.aslrShenanigansDetected = true;
-    simulation_main(argc, argv);
-    failWithError("simulation_main returned.");
-  }
-#endif
-
   // Remap `stdin` and `stdout` so we can use the original `stdin` and `stdout`
   // for commands and messages.
   int stdinCopy = dup(STDIN_FILENO);

svsim/src/main/scala/Backend.scala

@@ -213,10 +213,6 @@ final object Backend {
     /** Verilator does not currently support delay (`#delay`) in DPI functions, so we omit the SystemVerilog definition of the `run_simulation` function and instead provide a C implementation.
       */
     val supportsDelayInPublicFunctions = "SVSIM_BACKEND_SUPPORTS_DELAY_IN_PUBLIC_FUNCTIONS"
-
-    /** VCS first checks whether address-space layout randomization (ASLR) is enabled, and if it is, _helpfully_ relaunches this executable with ASLR disabled. Unfortunately, this causes code executed prior to `simulation_main` to be executed twice, which is problematic, especially since we redirect `stdin` and `stdout`.
-      */
-    val backendEngagesInASLRShenanigans = "SVSIM_BACKEND_ENGAGES_IN_ASLR_SHENANIGANS"
   }
 
   object Exceptions {

svsim/src/main/scala/vcs/Backend.scala

@@ -378,8 +378,6 @@ final class Backend(
               Seq(
                 // Enable VCS support
                 s"-D${svsim.Backend.HarnessCompilationFlags.enableVCSSupport}",
-                // VCS engages in ASLR shenanigans
-                s"-D${svsim.Backend.HarnessCompilationFlags.backendEngagesInASLRShenanigans}",
               )
             )),
           ).collect {
@@ -422,6 +420,14 @@ final class Backend(
           backendSpecificSettings.simulationSettings.coverageDirectory.map(_.toFlags).getOrElse(Seq.empty),
           backendSpecificSettings.simulationSettings.coverageName.map(_.toFlags).getOrElse(Seq.empty),
           commonSettings.simulationSettings.plusArgs.map(_.simulatorFlags),
+          // In order to support save/restore functionality, VCS will detect if
+          // Address Space Layout Randomization (ASLR) is ocurring when the
+          // simulation starts.  If it is, then VCS will relaunch the simulation
+          // with ASLR turned off.  This double-launch confuses svsim.  To avoid
+          // this, and because svsim doesn't support save/restore functionality,
+          // we turn off VCS save/restore features.  The simulation binary will
+          // then only run once.
+          Seq("-no_save")
         ).flatten,
         environment = environment
       )