added cli flags to enable "--careful" mode inspired by cargo careful

* based on [this PR](rust-fuzz/cargo-fuzz#292)
  to `cargo-fuzz` by @saethlin
* based on [cargo-careful](https://github.com/RalfJung/cargo-careful) by
  @RalfJung

cargo-libafl/src/options.rs

@@ -98,6 +98,19 @@ pub struct BuildOptions {
     /// Use a specific sanitizer
     pub sanitizer: Sanitizer,
 
+    #[clap(long = "build-std")]
+    /// Pass `-Zbuild-std` to cargo to build the standard library with the same build settings as
+    /// the fuzz target, such as debug assertions and sanitizers. This allows to identify a more
+    /// diverse set of bugs. But beware, some sanitizers might cause false alarms with the standard
+    /// library (e.g., thread sanitizer). Currently this conflicts with source-based coverage
+    /// instrumentation.
+    pub build_std: bool,
+
+    #[clap(short, long = "careful")]
+    /// enable "careful" mode: inspired by https://github.com/RalfJung/cargo-careful, this enables building the
+    /// standard library (implies --build-std) with debug assertions and extra const UB and init checks.
+    pub careful_mode: bool,
+
     #[clap(
         name = "triple",
         long = "target",
@@ -229,6 +242,8 @@ mod test {
             no_default_features: false,
             all_features: false,
             features: None,
+            build_std: false,
+            careful_mode: false,
             sanitizer: Sanitizer::Address,
             triple: String::from(crate::utils::default_target()),
             unstable_flags: Vec::new(),

cargo-libafl/src/options/coverage.rs

@@ -3,7 +3,7 @@ use crate::{
     project::FuzzProject,
     RunCommand,
 };
-use anyhow::Result;
+use anyhow::{bail, Result};
 use clap::{self, Parser};
 
 #[derive(Clone, Debug, Parser)]
@@ -27,6 +27,13 @@ pub struct Coverage {
 
 impl RunCommand for Coverage {
     fn run_command(&mut self) -> Result<()> {
+        if self.build.build_std {
+            bail!(
+                "-Zbuild-std is currently incompatible with -Zinstrument-coverage, \
+                    see https://github.com/rust-lang/wg-cargo-std-aware/issues/63"
+            );
+        }
+
         let project = FuzzProject::new(self.fuzz_dir_wrapper.fuzz_dir.clone())?;
         self.build.coverage = true;
         project.exec_coverage(self)

cargo-libafl/src/project.rs

@@ -159,7 +159,9 @@ impl FuzzProject {
         for flag in &build.unstable_flags {
             cmd.arg("-Z").arg(flag);
         }
-        if let Sanitizer::Memory = build.sanitizer {
+        if (matches!(build.sanitizer, Sanitizer::Memory) || build.build_std || build.careful_mode)
+            && !build.coverage
+        {
             cmd.arg("-Z").arg("build-std");
         }
 
@@ -202,8 +204,11 @@ impl FuzzProject {
         if build.triple.contains("-linux-") {
             rustflags.push_str(" -Cllvm-args=-sanitizer-coverage-stack-depth");
         }
-        if !build.release || build.debug_assertions {
-            rustflags.push_str(" -Cdebug-assertions");
+        if build.careful_mode {
+            rustflags.push_str(" -Zextra-const-ub-checks -Zstrict-init-checks --cfg careful");
+        }
+        if !build.release || build.debug_assertions || build.careful_mode {
+            rustflags.push_str(" -Cdebug-assertions=on");
         }
         if build.triple.contains("-msvc") {
             // The entrypoint is in the bundled libfuzzer rlib, this gets the linker to find it.