feat: introduce GCC disable environment variable

This change is to disable the GCC plugin version check for
GCC plugin and CMPLOG, to overcome the issues with incompatability
with expected GCC version and actual GCC version used to compile
using `AFL_GCC_DISABLE_VERSION_CHECK` environment variable.

5 files changed, 13 insertions, 7 deletions

diff --git a/include/envs.h b/include/envs.h
index 202de752..cca9baa8 100644
--- a/include/envs.h
+++ b/include/envs.h
@@ -52,9 +52,9 @@ static char *afl_environment_variables[] = {
     "AFL_FRIDA_VERBOSE", "AFL_OLD_FORKSERVER", "AFL_OPT_LEVEL",
     "AFL_FUZZER_ARGS",  // oss-fuzz
     "AFL_FUZZER_STATS_UPDATE_INTERVAL", "AFL_GDB", "AFL_GCC_ALLOWLIST",
-    "AFL_GCC_DENYLIST", "AFL_GCC_BLOCKLIST", "AFL_GCC_INSTRUMENT_FILE",
-    "AFL_GCC_OUT_OF_LINE", "AFL_GCC_SKIP_NEVERZERO", "AFL_GCJ",
-    "AFL_HANG_TMOUT", "AFL_FORKSRV_INIT_TMOUT", "AFL_HARDEN",
+    "AFL_GCC_DENYLIST", "AFL_GCC_BLOCKLIST", "AFL_GCC_DISABLE_VERSION_CHECK",
+    "AFL_GCC_INSTRUMENT_FILE", "AFL_GCC_OUT_OF_LINE", "AFL_GCC_SKIP_NEVERZERO",
+    "AFL_GCJ", "AFL_HANG_TMOUT", "AFL_FORKSRV_INIT_TMOUT", "AFL_HARDEN",
     "AFL_I_DONT_CARE_ABOUT_MISSING_CRASHES", "AFL_IGNORE_PROBLEMS",
     "AFL_IGNORE_PROBLEMS_COVERAGE", "AFL_IGNORE_SEED_PROBLEMS",
     "AFL_IGNORE_TIMEOUTS", "AFL_IGNORE_UNKNOWN_ENVS", "AFL_IMPORT_FIRST",
diff --git a/instrumentation/README.gcc_plugin.md b/instrumentation/README.gcc_plugin.md
index 011a574a..34004dc7 100644
--- a/instrumentation/README.gcc_plugin.md
+++ b/instrumentation/README.gcc_plugin.md
@@ -51,7 +51,10 @@ The idea and much of the implementation comes from Laszlo Szekeres.
 In order to leverage this mechanism, you need to have modern enough GCC (>=
 version 4.5.0) and the plugin development headers installed on your system. That
 should be all you need. On Debian machines, these headers can be acquired by
-installing the `gcc-VERSION-plugin-dev` packages.
+installing the `gcc-VERSION-plugin-dev` packages. If you're compiling a GCC 
+plugin that differs from the system-installed version and encounter issues 
+with version checks, you can use the `AFL_GCC_DISABLE_VERSION_CHECK` environment 
+variable.
 
 To build the instrumentation itself, type `make`. This will generate binaries
 called `afl-gcc-fast` and `afl-g++-fast` in the parent directory.
diff --git a/instrumentation/afl-gcc-cmplog-pass.so.cc b/instrumentation/afl-gcc-cmplog-pass.so.cc
index 774dd5fd..38fce961 100644
--- a/instrumentation/afl-gcc-cmplog-pass.so.cc
+++ b/instrumentation/afl-gcc-cmplog-pass.so.cc
@@ -370,7 +370,8 @@ Set AFL_QUIET in the environment to silence it.\n\
 int plugin_init(struct plugin_name_args   *info,
                 struct plugin_gcc_version *version) {
 
-  if (!plugin_default_version_check(version, &gcc_version))
+  if (!plugin_default_version_check(version, &gcc_version) &&
+      !getenv("AFL_GCC_DISABLE_VERSION_CHECK"))
     FATAL(G_("GCC and plugin have incompatible versions, expected GCC %s, "
              "is %s"),
           gcc_version.basever, version->basever);
diff --git a/instrumentation/afl-gcc-cmptrs-pass.so.cc b/instrumentation/afl-gcc-cmptrs-pass.so.cc
index 96bd5ba8..360b035a 100644
--- a/instrumentation/afl-gcc-cmptrs-pass.so.cc
+++ b/instrumentation/afl-gcc-cmptrs-pass.so.cc
@@ -338,7 +338,8 @@ Set AFL_QUIET in the environment to silence it.\n\
 int plugin_init(struct plugin_name_args   *info,
                 struct plugin_gcc_version *version) {
 
-  if (!plugin_default_version_check(version, &gcc_version))
+  if (!plugin_default_version_check(version, &gcc_version) &&
+      !getenv("AFL_GCC_DISABLE_VERSION_CHECK"))
     FATAL(G_("GCC and plugin have incompatible versions, expected GCC %s, "
              "is %s"),
           gcc_version.basever, version->basever);
diff --git a/instrumentation/afl-gcc-pass.so.cc b/instrumentation/afl-gcc-pass.so.cc
index 41b1e5af..26f7bd19 100644
--- a/instrumentation/afl-gcc-pass.so.cc
+++ b/instrumentation/afl-gcc-pass.so.cc
@@ -478,7 +478,8 @@ Specify -frandom-seed for reproducible instrumentation.\n\
 int plugin_init(struct plugin_name_args   *info,
                 struct plugin_gcc_version *version) {
 
-  if (!plugin_default_version_check(version, &gcc_version))
+  if (!plugin_default_version_check(version, &gcc_version) &&
+      !getenv("AFL_GCC_DISABLE_VERSION_CHECK"))
     FATAL(G_("GCC and plugin have incompatible versions, expected GCC %s, "
              "is %s"),
           gcc_version.basever, version->basever);