[Driver] Support for disabling sanitizer runtime linking

[phosek]

Summary

This change introduces a pair of -fsanitize-link-runtime and
-fno-sanitize-link-runtime flags which can be used to control linking of
sanitizer runtimes. This is useful in certain environments like kernels
where existing runtime libraries cannot be used.

[morehouse]

LGTM

[MaskRay]

There is an existing option -fsanitize-minimal-runtime, will -fsanitize-no-runtime be a name providing more consistency?

[pcc]

It's also worth asking whether -nodefaultlibs would work for this use case as @filcab suggested on D64547.

[phosek]

In D65029#1594437, @pcc wrote:

It's also worth asking whether -nodefaultlibs would work for this use case as @filcab suggested on D64547.

It wouldn't, -nodefaultlibs (same as -nostdlib) disables linking of runtime dependencies, but not the runtime itself, e.g. -fsanitize=address -nodefaultlibs disables linking of -lpthread -lrt -lm -ldl which are all dependencies of ASan, but doesn't disable linking of libclang_rt.asan.a which is what we care about.

In D65029#1594409, @MaskRay wrote:

There is an existing option -fsanitize-minimal-runtime, will -fsanitize-no-runtime be a name providing more consistency?

That's fine with me, I used -f[no-]sanitize-link-deps for consistency with XRay, but -fsanitize-no-runtime would work as well.

[phosek]

I've updated the change and renamed the flag to -fsanitize-no-runtime although I'm not sure if it's necessarily better. I was thinking that ideal interface might be -fsanitize-runtime=(none|minimal|shared|static) which could also replace -fshared-libsan and -fstatic-libsan, but it'd be a breaking change so we might have to keep the existing flag and maybe print a deprecation warning. WDYT?

[MaskRay]

In D65029#1613315, @phosek wrote:

I've updated the change and renamed the flag to -fsanitize-no-runtime although I'm not sure if it's necessarily better. I was thinking that ideal interface might be -fsanitize-runtime=(none|minimal|shared|static) which could also replace -fshared-libsan and -fstatic-libsan, but it'd be a breaking change so we might have to keep the existing flag and maybe print a deprecation warning. WDYT?

+1 for -fsanitize-runtime=

[phosek]

I've decided to go with the original -f[no-]sanitize-link-deps: -fsanitize-minimal-runtime is also a cc1 flag which affects codegen, -fshared-libsan and -fstatic-libsan are orthogonal, e.g. it's possible to have minimal shared or static runtime, so these really need to be different flags.

[phosek]

One more change, I went with -fsanitize-runtime and -fno-sanitize-runtime in the end which seems like the best fit.

clang/include/clang/Driver/Options.td

def fno_sanitize_thread_atomics : Flag<["-"], "fno-sanitize-thread-atomics">,
                                   Group<f_clang_Group>,
                                   Flags<[CoreOption, DriverOption]>,
                                   HelpText<"Disable atomic operations instrumentation in ThreadSanitizer">;
 def fsanitize_undefined_strip_path_components_EQ : Joined<["-"], "fsanitize-undefined-strip-path-components=">,
   Group<f_clang_Group>, MetaVarName<"<number>">,
   HelpText<"Strip (or keep only, if negative) a given number of path components "
            "when emitting check metadata.">;
 
+def fsanitize_link_deps : Flag<["-"], "fsanitize-link-deps">,
+                          Group<f_Group>,
+                          Flags<[CC1Option]>,
+                          HelpText<"Enable linking of sanitizer dependencies">;
+def fno_sanitize_link_deps : Flag<["-"], "fno-sanitize-link-deps">,
+                             Group<f_Group>,
+                             Flags<[CC1Option]>,
+                             HelpText<"Disable linking of sanitizer dependencies">;
+
 } // end -f[no-]sanitize* flags
 
 def funsafe_math_optimizations : Flag<["-"], "funsafe-math-optimizations">,
   Group<f_Group>;
 def fno_unsafe_math_optimizations : Flag<["-"], "fno-unsafe-math-optimizations">,
   Group<f_Group>;
 def fassociative_math : Flag<["-"], "fassociative-math">, Group<f_Group>;
 def fno_associative_math : Flag<["-"], "fno-associative-math">, Group<f_Group>;

clang/lib/Driver/ToolChains/CommonArgs.cpp

if (SanArgs.needsScudoRt()) {
     }
   }
 }
 
 // Should be called before we add system libraries (C++ ABI, libstdc++/libc++,
 // C runtime, etc). Returns true if sanitizer system deps need to be linked in.
 bool tools::addSanitizerRuntimes(const ToolChain &TC, const ArgList &Args,
                                  ArgStringList &CmdArgs) {
+  if (!Args.hasFlag(options::OPT_fsanitize_link_deps,
+                    options::OPT_fno_sanitize_link_deps, true))
+    return false;
+
   SmallVector<StringRef, 4> SharedRuntimes, StaticRuntimes,
       NonWholeStaticRuntimes, HelperStaticRuntimes, RequiredSymbols;
   collectSanitizerRuntimes(TC, Args, SharedRuntimes, StaticRuntimes,
                            NonWholeStaticRuntimes, HelperStaticRuntimes,
                            RequiredSymbols);
 
   // Inject libfuzzer dependencies.
   if (TC.getSanitizerArgs().needsFuzzer()

clang/test/Driver/sanitizer-ld.c

 // CHECK-DSO_SHARED-HWASAN-AARCH64-LINUX: "-pie"
 // CHECK-DSO-SHARED-HWASAN-AARCH64-LINUX-NOT: "-lc"
 // CHECK-DSO-SHARED-HWASAN-AARCH64-LINUX: libclang_rt.hwasan-aarch64.so"
 // CHECK-DSO-SHARED-HWASAN-AARCH64-LINUX-NOT: "-lpthread"
 // CHECK-DSO-SHARED-HWASAN-AARCH64-LINUX-NOT: "-lrt"
 // CHECK-DSO-SHARED-HWASAN-AARCH64-LINUX-NOT: "-ldl"
 // CHECK-DSO-SHARED-HWASAN-AARCH64-LINUX-NOT: "--export-dynamic"
 // CHECK-DSO-SHARED-HWASAN-AARCH64-LINUX-NOT: "--dynamic-list"
+
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -target i386-unknown-linux -fuse-ld=ld -fsanitize=address -fsanitize-link-deps \
+// RUN:     -resource-dir=%S/Inputs/resource_dir \
+// RUN:     --sysroot=%S/Inputs/basic_linux_tree \
+// RUN:   | FileCheck --check-prefix=CHECK-SANITIZE-LINK-DEPS %s
+//
+// CHECK-SANITIZE-LINK-DEPS: libclang_rt.asan-i386.a"
+
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -target i386-unknown-linux -fuse-ld=ld -fsanitize=address -fno-sanitize-link-deps \
+// RUN:     -resource-dir=%S/Inputs/resource_dir \
+// RUN:     --sysroot=%S/Inputs/basic_linux_tree \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-SANITIZE-LINK-DEPS %s
+//
+// CHECK-NO-SANITIZE-LINK-DEPS-NOT: libclang_rt.asan-i386.a"