Add `--aslr` and `--no-aslr` options.

Changes

@@ -25,6 +25,7 @@ Verilator 5.041 devel
 * Add error on `virtual new` (#6486). [Alex Solomatnikov]
 * Add error on ranges with tristate values (#6534). [Alex Solomatnikov]
 * Add NORETURN warning on functions without return values (#6534). [Alex Solomatnikov]
+* Add `--aslr` and `--no-aslr` options.
 * Deprecate sensitivity list on public_flat_rw attributes (#6443). [Geza Lore]
 * Deprecate clocker attribute and --clk option (#6463). [Geza Lore]
 * Deprecate '--make cmake' option (#6540). [Geza Lore]

bin/verilator

@@ -28,6 +28,7 @@ autoflush STDOUT 1;
 autoflush STDERR 1;
 
 $Debug = 0;
+my $opt_aslr;
 my $opt_gdb;
 my $opt_rr;
 my $opt_gdbbt;
@@ -56,6 +57,7 @@ if (! GetOptions(
           "debug"            => \&debug,
           # "version!"       => \&version,   # Also passthru'ed
           # Switches
+          "aslr!"            => \$opt_aslr,
           "gdb!"             => \$opt_gdb,
           "gdbbt!"           => \$opt_gdbbt,
           "quiet!"           => \$opt_quiet_exit,  # As -quiet implies -quiet-exit
@@ -97,7 +99,7 @@ my @quoted_sw = map { sh_escape($_) } @Opt_Verilator_Sw;
 if ($opt_gdb) {
     # Generic GDB interactive
     run (ulimit_stack_unlimited()
-         . aslr_off()
+         . aslr(0)
          . ($ENV{VERILATOR_GDB} || "gdb")
          . " " . verilator_bin()
          # Note, uncomment to set breakpoints before running:
@@ -114,13 +116,13 @@ if ($opt_gdb) {
 } elsif ($opt_rr) {
     # Record with rr
     run (ulimit_stack_unlimited()
-         . aslr_off()
+         . aslr(0)
          . "rr record " . verilator_bin()
          . " " . join(' ', @quoted_sw));
 } elsif ($opt_gdbbt && $Debug) {
     # Run under GDB to get gdbbt
     run (ulimit_stack_unlimited()
-         . aslr_off()
+         . aslr(0)
          . "gdb"
          . " " . verilator_bin()
          . " --batch --quiet --return-child-result"
@@ -135,19 +137,19 @@ if ($opt_gdb) {
         );
 
     run (ulimit_stack_unlimited()
-         . aslr_off()
+         . aslr(0)
          . $valgrind_bin
          . " " . verilator_bin()
          . " " . join(' ', @quoted_sw));
 } elsif ($Debug) {
     # Debug
     run(ulimit_stack_unlimited()
-        . aslr_off()
+        . aslr(0)
         . verilator_bin()
         . " " . join(' ', @quoted_sw));
 } else {
     # Normal, non gdb
-    run(ulimit_stack_unlimited() . verilator_bin() . " " . join(' ', @quoted_sw));
+    run(ulimit_stack_unlimited() . aslr(1) . verilator_bin() . " " . join(' ', @quoted_sw));
 }
 
 #----------------------------------------------------------------------
@@ -192,13 +194,16 @@ sub gdb_works {
     return $status == 0;
 }
 
-sub aslr_off {
-    my $ok = `setarch --addr-no-randomize echo ok 2>/dev/null` || "";
-    if ($ok =~ /ok/) {
-        return "setarch --addr-no-randomize ";
-    } else {
-        return "";
+sub aslr {
+    my $want_on = shift;
+    $want_on = $opt_aslr if defined $opt_aslr;
+    if (!$want_on) {
+        my $ok = `setarch --addr-no-randomize echo ok 2>/dev/null` || "";
+        if ($ok =~ /ok/) {
+            return "setarch --addr-no-randomize ";
+        }
     }
+    return "";
 }
 
 sub ulimit_stack_unlimited {
@@ -325,6 +330,7 @@ detailed descriptions of these arguments.
      +1800-2012ext+<ext>        Use SystemVerilog 2012 with file extension <ext>
      +1800-2017ext+<ext>        Use SystemVerilog 2017 with file extension <ext>
      +1800-2023ext+<ext>        Use SystemVerilog 2023 with file extension <ext>
+    --no-aslr                   Disable address space layout randomization
     --no-assert                 Disable all assertions
     --no-assert-case            Disable unique/unique0/priority-case assertions
     --autoflush                 Flush streams after all $displays

docs/guide/exe_verilator.rst

@@ -88,12 +88,23 @@ Summary:
       grammar and other semantic extensions which might not be legal when
       set to an older standard.
 
+.. option:: --aslr
+
+.. option:: --no-aslr
+
+   Rarely needed - for developer use. With `--aslr`, do not change the
+   system default as to using Linux address space layout randomization
+   (ASLR).  With `--no-aslr` attempt to disable ASLR. If not specified,
+   ASLR will be disabled only when using :vlopt:`--debug` (or similar
+   debug-related options), so that pointers have more deterministic values,
+   aiding repeatability.
+
 .. option:: --no-assert
 
    Disable all assertions. Implies :vlopt:`--no-assert-case`.
 
-   In versions before 5.038, these were disabled by default, and `--assert`
-   was required to enable assertions.
+   In versions before 5.038, assertions were disabled by default, and
+   `--assert` was required to enable assertions.
 
 .. option:: --no-assert-case
 

docs/spelling.txt

@@ -531,6 +531,7 @@ architected
 args
 arrarys
 asan
+aslr
 assertOn
 assertcontrol
 astgen

src/V3Options.cpp

@@ -1237,6 +1237,7 @@ void V3Options::parseOptsList(FileLine* fl, const string& optdir, int argc,
                 [this](const char* optp) { addLangExt(optp, V3LangCode::L1800_2023); });
 
     // Minus options
+    DECL_OPTION("-aslr", CbOnOff, [](bool) {});  // Processed only in bin/verilator shell
     DECL_OPTION("-assert", CbOnOff, [this](bool flag) {
         m_assert = flag;
         m_assertCase = flag;

test_regress/t/t_flag_aslr.py

@@ -0,0 +1,17 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2024 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('vlt')
+test.top_filename = 't/t_EXAMPLE.v'
+
+test.lint(v_flags2=["--aslr"])
+
+test.passes()

test_regress/t/t_flag_aslr_no.py

@@ -0,0 +1,17 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2024 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('vlt')
+test.top_filename = 't/t_EXAMPLE.v'
+
+test.lint(v_flags2=["--no-aslr"])
+
+test.passes()