[Driver] Enable ShadowCallStack, not SafeStack, by default on AArch64 Fuchsia

[mcgrathr]

Summary

On AArch64, Fuchsia fully supports both SafeStack and ShadowCallStack ABIs.
The latter is now preferred and will be the default. It's possible to
enable both simultaneously, but ShadowCallStack is believed to have most
of the practical benefit of SafeStack with less cost.

[mcgrathr]

This should land only after we've done our first stages of downstream roll-out and burn-in testing. But setting it up now.

[jakehehrlich]

Landing aside, this looks good to me

[mcgrathr]

rebased

[mcgrathr]

It's time to land this now. Can one of you commit it for me?

[leonardchan]

Manually closed since git push didn't seem to automatically close this. Committed under https://github.com/llvm/llvm-project/commit/85b718f53a3575bca2f1b7fdb1b3aaa6df7c10e3.

clang/lib/Driver/ToolChains/Fuchsia.cpp

SanitizerMask Fuchsia::getSupportedSanitizers() const {
   Res |= SanitizerKind::Fuzzer;
   Res |= SanitizerKind::FuzzerNoLink;
   Res |= SanitizerKind::SafeStack;
   Res |= SanitizerKind::Scudo;
   return Res;
 }
 
 SanitizerMask Fuchsia::getDefaultSanitizers() const {
-  return SanitizerKind::SafeStack;
+  SanitizerMask Res;
+  if (getTriple().getArch() == llvm::Triple::aarch64)
+    Res |= SanitizerKind::ShadowCallStack;
+  else
+    Res |= SanitizerKind::SafeStack;
+  return Res;
 }

clang/test/Driver/fuchsia.c

 // RUN: %clang %s -### -no-canonical-prefixes --target=x86_64-fuchsia \
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     --sysroot=%S/platform -fuse-ld=lld 2>&1 \
 // RUN:     | FileCheck -check-prefixes=CHECK,CHECK-X86_64 %s
 // RUN: %clang %s -### -no-canonical-prefixes --target=aarch64-fuchsia \
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     --sysroot=%S/platform -fuse-ld=lld 2>&1 \
 // RUN:     | FileCheck -check-prefixes=CHECK,CHECK-AARCH64 %s
 // CHECK: {{.*}}clang{{.*}}" "-cc1"
 // CHECK: "--mrelax-relocations"
 // CHECK: "-munwind-tables"
 // CHECK: "-fuse-init-array"
 // CHECK: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
 // CHECK: "-isysroot" "[[SYSROOT:[^"]+]]"
 // CHECK: "-internal-externc-isystem" "[[SYSROOT]]{{/|\\\\}}include"
-// CHECK: "-fsanitize=safe-stack"
+// CHECK-AARCH64: "-fsanitize=shadow-call-stack"
+// CHECK-X86_64: "-fsanitize=safe-stack"
 // CHECK: "-stack-protector" "2"
 // CHECK: "-fno-common"
 // CHECK: {{.*}}ld.lld{{.*}}" "-z" "rodynamic" "-z" "separate-loadable-segments"
 // CHECK: "--sysroot=[[SYSROOT]]"
 // CHECK: "-pie"
 // CHECK: "--build-id"
 // CHECK: "--hash-style=gnu"
 // CHECK: "-dynamic-linker" "ld.so.1"

 // CHECK-ASAN-X86: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}libclang_rt.asan-preinit.a"
 
 // RUN: %clang %s -### --target=aarch64-fuchsia \
 // RUN:     -fsanitize=address 2>&1 \
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     -fuse-ld=lld \
 // RUN:     | FileCheck %s -check-prefix=CHECK-ASAN-AARCH64
 // CHECK-ASAN-AARCH64: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
-// CHECK-ASAN-AARCH64: "-fsanitize=address"
+// CHECK-ASAN-AARCH64: "-fsanitize=address,shadow-call-stack"
 // CHECK-ASAN-AARCH64: "-fsanitize-address-globals-dead-stripping"
 // CHECK-ASAN-AARCH64: "-dynamic-linker" "asan/ld.so.1"
 // CHECK-ASAN-AARCH64: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}aarch64-fuchsia{{/|\\\\}}libclang_rt.asan.so"
 // CHECK-ASAN-AARCH64: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}aarch64-fuchsia{{/|\\\\}}libclang_rt.asan-preinit.a"
 
 // RUN: %clang %s -### --target=x86_64-fuchsia \
 // RUN:     -fsanitize=address -fPIC -shared 2>&1 \
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \

 // CHECK-FUZZER-X86: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}libclang_rt.fuzzer.a"
 
 // RUN: %clang %s -### --target=aarch64-fuchsia \
 // RUN:     -fsanitize=fuzzer 2>&1 \
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     -fuse-ld=lld \
 // RUN:     | FileCheck %s -check-prefix=CHECK-FUZZER-AARCH64
 // CHECK-FUZZER-AARCH64: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
-// CHECK-FUZZER-AARCH64: "-fsanitize=fuzzer,fuzzer-no-link,safe-stack"
+// CHECK-FUZZER-AARCH64: "-fsanitize=fuzzer,fuzzer-no-link,shadow-call-stack"
 // CHECK-FUZZER-AARCH64: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}aarch64-fuchsia{{/|\\\\}}libclang_rt.fuzzer.a"
 
 // RUN: %clang %s -### --target=x86_64-fuchsia \
 // RUN:     -fsanitize=scudo 2>&1 \
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     -fuse-ld=lld \
 // RUN:     | FileCheck %s -check-prefix=CHECK-SCUDO-X86
 // CHECK-SCUDO-X86: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
 // CHECK-SCUDO-X86: "-fsanitize=safe-stack,scudo"
 // CHECK-SCUDO-X86: "-pie"
 // CHECK-SCUDO-X86: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}libclang_rt.scudo.so"
 
 // RUN: %clang %s -### --target=aarch64-fuchsia \
 // RUN:     -fsanitize=scudo 2>&1 \
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     -fuse-ld=lld \
 // RUN:     | FileCheck %s -check-prefix=CHECK-SCUDO-AARCH64
 // CHECK-SCUDO-AARCH64: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
-// CHECK-SCUDO-AARCH64: "-fsanitize=safe-stack,scudo"
+// CHECK-SCUDO-AARCH64: "-fsanitize=shadow-call-stack,scudo"
 // CHECK-SCUDO-AARCH64: "-pie"
 // CHECK-SCUDO-AARCH64: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}aarch64-fuchsia{{/|\\\\}}libclang_rt.scudo.so"
 
 // RUN: %clang %s -### --target=x86_64-fuchsia \
 // RUN:     -fsanitize=scudo -fPIC -shared 2>&1 \
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     -fuse-ld=lld \
 // RUN:     | FileCheck %s -check-prefix=CHECK-SCUDO-SHARED