[UBsan] add -fsanitize-handler-preserve-all-regs flag (#168644)

This is currently a no op.
This will be supported for the minimal runtime in a follow up. This
allows
to improve codegen for fsanitize-recover by compiling the handlers with
[[clang::preserve_all]]. This makes sure that the caller does not need
to spill any registers. We do not expect this function to be called
frequently, so this is beneficial for code size.

Author: fmayer

clang/include/clang/Basic/CodeGenOptions.def

@@ -270,6 +270,8 @@ CODEGENOPT(SanitizeMemoryUseAfterDtor, 1, 0, Benign) ///< Enable use-after-delet
 CODEGENOPT(SanitizeCfiCrossDso, 1, 0, Benign) ///< Enable cross-dso support in CFI.
 CODEGENOPT(SanitizeMinimalRuntime, 1, 0, Benign) ///< Use "_minimal" sanitizer runtime for
                                                  ///< diagnostics.
+CODEGENOPT(SanitizeHandlerPreserveAllRegs, 1, 0, Benign) ///< Use "_preserve" sanitizer runtime for
+                                                 ///< diagnostics.
 CODEGENOPT(SanitizeCfiICallGeneralizePointers, 1, 0, Benign) ///< Generalize pointer types in
                                                              ///< CFI icall function signatures
 CODEGENOPT(SanitizeCfiICallNormalizeIntegers, 1, 0, Benign) ///< Normalize integer types in

clang/include/clang/Driver/SanitizerArgs.h

@@ -68,6 +68,7 @@ class SanitizerArgs {
   bool TsanAtomics = true;
   bool MinimalRuntime = false;
   bool TysanOutlineInstrumentation = true;
+  bool HandlerPreserveAllRegs = false;
   // True if cross-dso CFI support if provided by the system (i.e. Android).
   bool ImplicitCfiRuntime = false;
   bool NeedsMemProfRt = false;

clang/include/clang/Options/Options.td

@@ -2666,6 +2666,15 @@ defm sanitize_minimal_runtime : BoolOption<"f", "sanitize-minimal-runtime",
   PosFlag<SetTrue>,
   NegFlag<SetFalse>>,
   Group<f_clang_Group>;
+defm sanitize_handler_preserve_all_regs
+    : BoolOption<
+          "f", "sanitize-handler-preserve-all-regs",
+          CodeGenOpts<"SanitizeHandlerPreserveAllRegs">, DefaultFalse,
+          PosFlag<SetTrue, [], [],
+                  "Enable handlers with preserve_all calling convention">,
+          NegFlag<SetFalse, [], [],
+                  "Disable handlers with preserve_all calling convention">>,
+      Group<f_clang_Group>;
 def fsanitize_link_runtime : Flag<["-"], "fsanitize-link-runtime">,
                            Group<f_clang_Group>;
 def fno_sanitize_link_runtime : Flag<["-"], "fno-sanitize-link-runtime">,

clang/lib/Driver/SanitizerArgs.cpp

@@ -423,6 +423,10 @@ SanitizerArgs::SanitizerArgs(const ToolChain &TC,
   MinimalRuntime =
       Args.hasFlag(options::OPT_fsanitize_minimal_runtime,
                    options::OPT_fno_sanitize_minimal_runtime, MinimalRuntime);
+  HandlerPreserveAllRegs =
+      Args.hasFlag(options::OPT_fsanitize_handler_preserve_all_regs,
+                   options::OPT_fno_sanitize_handler_preserve_all_regs,
+                   HandlerPreserveAllRegs);
 
   // The object size sanitizer should not be enabled at -O0.
   Arg *OptLevel = Args.getLastArg(options::OPT_O_Group);
@@ -1476,6 +1480,9 @@ void SanitizerArgs::addArgs(const ToolChain &TC, const llvm::opt::ArgList &Args,
   if (MinimalRuntime)
     CmdArgs.push_back("-fsanitize-minimal-runtime");
 
+  if (HandlerPreserveAllRegs)
+    CmdArgs.push_back("-fsanitize-handler-preserve-all-regs");
+
   if (AsanFieldPadding)
     CmdArgs.push_back(Args.MakeArgString("-fsanitize-address-field-padding=" +
                                          Twine(AsanFieldPadding)));

clang/test/Driver/fsanitize.c

@@ -984,6 +984,11 @@
 // CHECK-UBSAN-MINIMAL: "-fsanitize={{((signed-integer-overflow|integer-divide-by-zero|shift-base|shift-exponent|unreachable|return|vla-bound|alignment|null|pointer-overflow|float-cast-overflow|array-bounds|enum|bool|builtin|returns-nonnull-attribute|nonnull-attribute|function),?){18}"}}
 // CHECK-UBSAN-MINIMAL: "-fsanitize-minimal-runtime"
 
+// RUN: %clang --target=x86_64-linux-gnu -fsanitize=undefined -fsanitize-minimal-runtime -fsanitize-handler-preserve-all-regs %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-UBSAN-MINIMAL-PRESERVE
+// CHECK-UBSAN-MINIMAL-PRESERVE: "-fsanitize={{((signed-integer-overflow|integer-divide-by-zero|shift-base|shift-exponent|unreachable|return|vla-bound|alignment|null|pointer-overflow|float-cast-overflow|array-bounds|enum|bool|builtin|returns-nonnull-attribute|nonnull-attribute|function),?){18}"}}
+// CHECK-UBSAN-MINIMAL-PRESERVE: "-fsanitize-minimal-runtime"
+// CHECK-UBSAN-MINIMAL-PRESERVE: "-fsanitize-handler-preserve-all-regs
+
 // RUN: %clang --target=x86_64-linux-gnu -fsanitize=integer -fsanitize-trap=integer %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-INTSAN-TRAP
 // CHECK-INTSAN-TRAP: "-fsanitize-trap=integer-divide-by-zero,shift-base,shift-exponent,signed-integer-overflow,unsigned-integer-overflow,unsigned-shift-base,implicit-unsigned-integer-truncation,implicit-signed-integer-truncation,implicit-integer-sign-change"