cfi-icall: Allow the jump table to be optionally made non-canonical.
The default behavior of Clang's indirect function call checker will replace
the address of each CFI-checked function in the output file's symbol table
with the address of a jump table entry which will pass CFI checks. We refer
to this as making the jump table `canonical`. This property allows code that
was not compiled with ``-fsanitize=cfi-icall`` to take a CFI-valid address
of a function, but it comes with a couple of caveats that are especially
relevant for users of cross-DSO CFI:
- There is a performance and code size overhead associated with each
exported function, because each such function must have an associated
jump table entry, which must be emitted even in the common case where the
function is never address-taken anywhere in the program, and must be used
even for direct calls between DSOs, in addition to the PLT overhead.
- There is no good way to take a CFI-valid address of a function written in
assembly or a language not supported by Clang. The reason is that the code
generator would need to insert a jump table in order to form a CFI-valid
address for assembly functions, but there is no way in general for the
code generator to determine the language of the function. This may be
possible with LTO in the intra-DSO case, but in the cross-DSO case the only
information available is the function declaration. One possible solution
is to add a C wrapper for each assembly function, but these wrappers can
present a significant maintenance burden for heavy users of assembly in
addition to adding runtime overhead.
For these reasons, we provide the option of making the jump table non-canonical
with the flag ``-fno-sanitize-cfi-canonical-jump-tables``. When the jump
table is made non-canonical, symbol table entries point directly to the
function body. Any instances of a function's address being taken in C will
be replaced with a jump table address.
This scheme does have its own caveats, however. It does end up breaking
function address equality more aggressively than the default behavior,
especially in cross-DSO mode which normally preserves function address
equality entirely.
Furthermore, it is occasionally necessary for code not compiled with
``-fsanitize=cfi-icall`` to take a function address that is valid
for CFI. For example, this is necessary when a function's address
is taken by assembly code and then called by CFI-checking C code. The
``__attribute__((cfi_jump_table_canonical))`` attribute may be used to make
the jump table entry of a specific function canonical so that the external
code will end up taking a address for the function that will pass CFI checks.
Fixes PR41972.
Differential Revision: https://reviews.llvm.org/D65629
llvm-svn: 368495
diff --git a/clang/docs/ControlFlowIntegrity.rst b/clang/docs/ControlFlowIntegrity.rst
index f57bdf5..03e27d3 100644
--- a/clang/docs/ControlFlowIntegrity.rst
+++ b/clang/docs/ControlFlowIntegrity.rst
@@ -235,6 +235,54 @@
``-fsanitize-cfi-icall-generalize-pointers`` is not compatible with
``-fsanitize-cfi-cross-dso``.
+.. _cfi-canonical-jump-tables:
+
+``-fsanitize-cfi-canonical-jump-tables``
+----------------------------------------
+
+The default behavior of Clang's indirect function call checker will replace
+the address of each CFI-checked function in the output file's symbol table
+with the address of a jump table entry which will pass CFI checks. We refer
+to this as making the jump table `canonical`. This property allows code that
+was not compiled with ``-fsanitize=cfi-icall`` to take a CFI-valid address
+of a function, but it comes with a couple of caveats that are especially
+relevant for users of cross-DSO CFI:
+
+- There is a performance and code size overhead associated with each
+ exported function, because each such function must have an associated
+ jump table entry, which must be emitted even in the common case where the
+ function is never address-taken anywhere in the program, and must be used
+ even for direct calls between DSOs, in addition to the PLT overhead.
+
+- There is no good way to take a CFI-valid address of a function written in
+ assembly or a language not supported by Clang. The reason is that the code
+ generator would need to insert a jump table in order to form a CFI-valid
+ address for assembly functions, but there is no way in general for the
+ code generator to determine the language of the function. This may be
+ possible with LTO in the intra-DSO case, but in the cross-DSO case the only
+ information available is the function declaration. One possible solution
+ is to add a C wrapper for each assembly function, but these wrappers can
+ present a significant maintenance burden for heavy users of assembly in
+ addition to adding runtime overhead.
+
+For these reasons, we provide the option of making the jump table non-canonical
+with the flag ``-fno-sanitize-cfi-canonical-jump-tables``. When the jump
+table is made non-canonical, symbol table entries point directly to the
+function body. Any instances of a function's address being taken in C will
+be replaced with a jump table address.
+
+This scheme does have its own caveats, however. It does end up breaking
+function address equality more aggressively than the default behavior,
+especially in cross-DSO mode which normally preserves function address
+equality entirely.
+
+Furthermore, it is occasionally necessary for code not compiled with
+``-fsanitize=cfi-icall`` to take a function address that is valid
+for CFI. For example, this is necessary when a function's address
+is taken by assembly code and then called by CFI-checking C code. The
+``__attribute__((cfi_canonical_jump_table))`` attribute may be used to make
+the jump table entry of a specific function canonical so that the external
+code will end up taking a address for the function that will pass CFI checks.
``-fsanitize=cfi-icall`` and ``-fsanitize=function``
----------------------------------------------------
diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index 9f9292d..db13e91 100644
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -2436,6 +2436,12 @@
let ASTNode = 0;
}
+def CFICanonicalJumpTable : InheritableAttr {
+ let Spellings = [Clang<"cfi_canonical_jump_table">];
+ let Subjects = SubjectList<[Function], ErrorDiag>;
+ let Documentation = [CFICanonicalJumpTableDocs];
+}
+
// C/C++ Thread safety attributes (e.g. for deadlock, data race checking)
// Not all of these attributes will be given a [[]] spelling. The attributes
// which require access to function parameter names cannot use the [[]] spelling
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index 0f10d90..1d6c1ab 100644
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -2221,6 +2221,18 @@
}];
}
+def CFICanonicalJumpTableDocs : Documentation {
+ let Category = DocCatFunction;
+ let Heading = "cfi_canonical_jump_table";
+ let Content = [{
+.. _langext-cfi_canonical_jump_table:
+
+Use ``__attribute__((cfi_canonical_jump_table))`` on a function declaration to
+make the function's CFI jump table canonical. See :ref:`the CFI documentation
+<cfi-canonical-jump-tables>` for more details.
+ }];
+}
+
def DocCatTypeSafety : DocumentationCategory<"Type Safety Checking"> {
let Content = [{
Clang supports additional attributes to enable checking type safety properties
diff --git a/clang/include/clang/Basic/CodeGenOptions.def b/clang/include/clang/Basic/CodeGenOptions.def
index 400711e..736f201 100644
--- a/clang/include/clang/Basic/CodeGenOptions.def
+++ b/clang/include/clang/Basic/CodeGenOptions.def
@@ -195,6 +195,8 @@
///< diagnostics.
CODEGENOPT(SanitizeCfiICallGeneralizePointers, 1, 0) ///< Generalize pointer types in
///< CFI icall function signatures
+CODEGENOPT(SanitizeCfiCanonicalJumpTables, 1, 0) ///< Make jump table symbols canonical
+ ///< instead of creating a local jump table.
CODEGENOPT(SanitizeCoverageType, 2, 0) ///< Type of sanitizer coverage
///< instrumentation.
CODEGENOPT(SanitizeCoverageIndirectCalls, 1, 0) ///< Enable sanitizer coverage
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 19022b4..0f2c314 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -1061,6 +1061,13 @@
def fsanitize_cfi_icall_generalize_pointers : Flag<["-"], "fsanitize-cfi-icall-generalize-pointers">,
Group<f_clang_Group>,
HelpText<"Generalize pointers in CFI indirect call type signature checks">;
+def fsanitize_cfi_canonical_jump_tables : Flag<["-"], "fsanitize-cfi-canonical-jump-tables">,
+ Group<f_clang_Group>,
+ HelpText<"Make the jump table addresses canonical in the symbol table">;
+def fno_sanitize_cfi_canonical_jump_tables : Flag<["-"], "fno-sanitize-cfi-canonical-jump-tables">,
+ Group<f_clang_Group>,
+ Flags<[CoreOption, DriverOption]>,
+ HelpText<"Do not make the jump table addresses canonical in the symbol table">;
def fsanitize_stats : Flag<["-"], "fsanitize-stats">,
Group<f_clang_Group>,
HelpText<"Enable sanitizer statistics gathering.">;
diff --git a/clang/include/clang/Driver/SanitizerArgs.h b/clang/include/clang/Driver/SanitizerArgs.h
index e7de509..c37499e 100644
--- a/clang/include/clang/Driver/SanitizerArgs.h
+++ b/clang/include/clang/Driver/SanitizerArgs.h
@@ -32,6 +32,7 @@
bool MsanUseAfterDtor = true;
bool CfiCrossDso = false;
bool CfiICallGeneralizePointers = false;
+ bool CfiCanonicalJumpTables = false;
int AsanFieldPadding = 0;
bool SharedRuntime = false;
bool AsanUseAfterScope = true;
diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index eafe266..f7d9c82 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -762,6 +762,9 @@
if (CGM.getCodeGenOpts().ProfileSampleAccurate)
Fn->addFnAttr("profile-sample-accurate");
+ if (D && D->hasAttr<CFICanonicalJumpTableAttr>())
+ Fn->addFnAttr("cfi-canonical-jump-table");
+
if (getLangOpts().OpenCL) {
// Add metadata for a kernel function.
if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D))
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index b650526..8943b40 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -535,6 +535,12 @@
getModule().addModuleFlag(llvm::Module::Override, "Cross-DSO CFI", 1);
}
+ if (LangOpts.Sanitize.has(SanitizerKind::CFIICall)) {
+ getModule().addModuleFlag(llvm::Module::Override,
+ "CFI Canonical Jump Tables",
+ CodeGenOpts.SanitizeCfiCanonicalJumpTables);
+ }
+
if (CodeGenOpts.CFProtectionReturn &&
Target.checkCFProtectionReturnSupported(getDiags())) {
// Indicate that we want to instrument return control flow protection.
@@ -1605,10 +1611,17 @@
F->setAlignment(2);
}
- // In the cross-dso CFI mode, we want !type attributes on definitions only.
- if (CodeGenOpts.SanitizeCfiCrossDso)
- if (auto *FD = dyn_cast<FunctionDecl>(D))
- CreateFunctionTypeMetadataForIcall(FD, F);
+ // In the cross-dso CFI mode with canonical jump tables, we want !type
+ // attributes on definitions only.
+ if (CodeGenOpts.SanitizeCfiCrossDso &&
+ CodeGenOpts.SanitizeCfiCanonicalJumpTables) {
+ if (auto *FD = dyn_cast<FunctionDecl>(D)) {
+ // Skip available_externally functions. They won't be codegen'ed in the
+ // current module anyway.
+ if (getContext().GetGVALinkageForFunction(FD) != GVA_AvailableExternally)
+ CreateFunctionTypeMetadataForIcall(FD, F);
+ }
+ }
// Emit type metadata on member functions for member function pointer checks.
// These are only ever necessary on definitions; we're guaranteed that the
@@ -1765,14 +1778,6 @@
if (isa<CXXMethodDecl>(FD) && !cast<CXXMethodDecl>(FD)->isStatic())
return;
- // Additionally, if building with cross-DSO support...
- if (CodeGenOpts.SanitizeCfiCrossDso) {
- // Skip available_externally functions. They won't be codegen'ed in the
- // current module anyway.
- if (getContext().GetGVALinkageForFunction(FD) == GVA_AvailableExternally)
- return;
- }
-
llvm::Metadata *MD = CreateMetadataIdentifierForType(FD->getType());
F->addTypeMetadata(0, MD);
F->addTypeMetadata(0, CreateMetadataIdentifierGeneralized(FD->getType()));
@@ -1849,8 +1854,11 @@
F->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
// Don't emit entries for function declarations in the cross-DSO mode. This
- // is handled with better precision by the receiving DSO.
- if (!CodeGenOpts.SanitizeCfiCrossDso)
+ // is handled with better precision by the receiving DSO. But if jump tables
+ // are non-canonical then we need type metadata in order to produce the local
+ // jump table.
+ if (!CodeGenOpts.SanitizeCfiCrossDso ||
+ !CodeGenOpts.SanitizeCfiCanonicalJumpTables)
CreateFunctionTypeMetadataForIcall(FD, F);
if (getLangOpts().OpenMP && FD->hasAttr<OMPDeclareSimdDeclAttr>())
diff --git a/clang/lib/Driver/SanitizerArgs.cpp b/clang/lib/Driver/SanitizerArgs.cpp
index 8e59e19..7d4cc53 100644
--- a/clang/lib/Driver/SanitizerArgs.cpp
+++ b/clang/lib/Driver/SanitizerArgs.cpp
@@ -636,6 +636,10 @@
D.Diag(diag::err_drv_argument_not_allowed_with)
<< "-fsanitize-cfi-cross-dso"
<< "-fsanitize-cfi-icall-generalize-pointers";
+
+ CfiCanonicalJumpTables =
+ Args.hasFlag(options::OPT_fsanitize_cfi_canonical_jump_tables,
+ options::OPT_fno_sanitize_cfi_canonical_jump_tables, true);
}
Stats = Args.hasFlag(options::OPT_fsanitize_stats,
@@ -976,6 +980,9 @@
if (CfiICallGeneralizePointers)
CmdArgs.push_back("-fsanitize-cfi-icall-generalize-pointers");
+ if (CfiCanonicalJumpTables)
+ CmdArgs.push_back("-fsanitize-cfi-canonical-jump-tables");
+
if (Stats)
CmdArgs.push_back("-fsanitize-stats");
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 7d1b196..fb5f1cc 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1139,6 +1139,8 @@
Opts.SanitizeCfiCrossDso = Args.hasArg(OPT_fsanitize_cfi_cross_dso);
Opts.SanitizeCfiICallGeneralizePointers =
Args.hasArg(OPT_fsanitize_cfi_icall_generalize_pointers);
+ Opts.SanitizeCfiCanonicalJumpTables =
+ Args.hasArg(OPT_fsanitize_cfi_canonical_jump_tables);
Opts.SanitizeStats = Args.hasArg(OPT_fsanitize_stats);
if (Arg *A = Args.getLastArg(
OPT_fsanitize_address_poison_custom_array_cookie,
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 950dcac..2a72f7d 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -7198,6 +7198,9 @@
// Interacts with -fstack-protector options.
handleSimpleAttribute<NoStackProtectorAttr>(S, D, AL);
break;
+ case ParsedAttr::AT_CFICanonicalJumpTable:
+ handleSimpleAttribute<CFICanonicalJumpTableAttr>(S, D, AL);
+ break;
case ParsedAttr::AT_StdCall:
case ParsedAttr::AT_CDecl:
case ParsedAttr::AT_FastCall:
diff --git a/clang/test/CodeGen/cfi-icall-canonical-jump-tables.c b/clang/test/CodeGen/cfi-icall-canonical-jump-tables.c
new file mode 100644
index 0000000..cf7ca42
--- /dev/null
+++ b/clang/test/CodeGen/cfi-icall-canonical-jump-tables.c
@@ -0,0 +1,24 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -fsanitize=cfi-icall -fsanitize-cfi-cross-dso -emit-llvm -o - %s | FileCheck --check-prefixes=CHECK,NOCANON %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -fsanitize=cfi-icall -fsanitize-cfi-cross-dso -fsanitize-cfi-canonical-jump-tables -emit-llvm -o - %s | FileCheck --check-prefixes=CHECK,CANON %s
+
+void ext(void);
+
+// CHECK: define void @f({{.*}} [[ATTR1:#[0-9]+]]
+void f() {
+ ext();
+}
+
+// NOCANON: declare !type {{.*}} @ext()
+// CANON: declare void @ext()
+
+// CHECK: define void @g({{.*}} [[ATTR2:#[0-9]+]]
+__attribute__((cfi_canonical_jump_table)) void g() {}
+
+// CHECK: [[ATTR1]] = {
+// CHECK-NOT: "cfi-canonical-jump-table"
+// CHECK: }
+
+// CHECK: [[ATTR2]] = { {{.*}} "cfi-canonical-jump-table" {{.*}} }
+
+// NOCANON: !{i32 4, !"CFI Canonical Jump Tables", i32 0}
+// CANON: !{i32 4, !"CFI Canonical Jump Tables", i32 1}
diff --git a/clang/test/CodeGen/cfi-icall-cross-dso.c b/clang/test/CodeGen/cfi-icall-cross-dso.c
index 67901c4..fbfe213 100644
--- a/clang/test/CodeGen/cfi-icall-cross-dso.c
+++ b/clang/test/CodeGen/cfi-icall-cross-dso.c
@@ -1,27 +1,27 @@
// RUN: %clang_cc1 -triple x86_64-unknown-linux -O1 -fno-experimental-new-pass-manager \
// RUN: -fsanitize=cfi-icall -fsanitize-cfi-cross-dso \
-// RUN: -emit-llvm -o - %s | FileCheck \
+// RUN: -fsanitize-cfi-canonical-jump-tables -emit-llvm -o - %s | FileCheck \
// RUN: --check-prefix=CHECK --check-prefix=CHECK-DIAG \
// RUN: --check-prefix=ITANIUM --check-prefix=ITANIUM-DIAG \
// RUN: %s
// RUN: %clang_cc1 -triple x86_64-unknown-linux -O1 -fno-experimental-new-pass-manager \
// RUN: -fsanitize=cfi-icall -fsanitize-cfi-cross-dso -fsanitize-trap=cfi-icall \
-// RUN: -emit-llvm -o - %s | FileCheck \
+// RUN: -fsanitize-cfi-canonical-jump-tables -emit-llvm -o - %s | FileCheck \
// RUN: --check-prefix=CHECK \
// RUN: --check-prefix=ITANIUM --check-prefix=ITANIUM-TRAP \
// RUN: %s
// RUN: %clang_cc1 -triple x86_64-pc-windows-msvc -O1 -fno-experimental-new-pass-manager \
// RUN: -fsanitize=cfi-icall -fsanitize-cfi-cross-dso \
-// RUN: -emit-llvm -o - %s | FileCheck \
+// RUN: -fsanitize-cfi-canonical-jump-tables -emit-llvm -o - %s | FileCheck \
// RUN: --check-prefix=CHECK --check-prefix=CHECK-DIAG \
// RUN: --check-prefix=MS --check-prefix=MS-DIAG \
// RUN: %s
// RUN: %clang_cc1 -triple x86_64-pc-windows-msvc -O1 -fno-experimental-new-pass-manager \
// RUN: -fsanitize=cfi-icall -fsanitize-cfi-cross-dso -fsanitize-trap=cfi-icall \
-// RUN: -emit-llvm -o - %s | FileCheck \
+// RUN: -fsanitize-cfi-canonical-jump-tables -emit-llvm -o - %s | FileCheck \
// RUN: --check-prefix=CHECK \
// RUN: --check-prefix=MS --check-prefix=MS-TRAP \
// RUN: %s
diff --git a/clang/test/Driver/fsanitize.c b/clang/test/Driver/fsanitize.c
index 0caac04..6e8e61b 100644
--- a/clang/test/Driver/fsanitize.c
+++ b/clang/test/Driver/fsanitize.c
@@ -621,6 +621,12 @@
// RUN: %clang -target x86_64-linux-gnu -fsanitize=cfi-icall -fsanitize-cfi-icall-generalize-pointers -fsanitize-cfi-cross-dso -fvisibility=hidden -flto -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-CFI-GENERALIZE-AND-CROSS-DSO
// CHECK-CFI-GENERALIZE-AND-CROSS-DSO: error: invalid argument '-fsanitize-cfi-cross-dso' not allowed with '-fsanitize-cfi-icall-generalize-pointers'
+// RUN: %clang -target x86_64-linux-gnu -fsanitize=cfi-icall -fsanitize-cfi-canonical-jump-tables -fvisibility=hidden -flto -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-CFI-CANONICAL-JUMP-TABLES
+// RUN: %clang -target x86_64-linux-gnu -fsanitize=cfi-icall -fno-sanitize-cfi-canonical-jump-tables -fvisibility=hidden -flto -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-NO-CFI-CANONICAL-JUMP-TABLES
+// RUN: %clang -target x86_64-linux-gnu -fsanitize=cfi-icall -fvisibility=hidden -flto -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-CFI-CANONICAL-JUMP-TABLES
+// CHECK-CFI-CANONICAL-JUMP-TABLES: -fsanitize-cfi-canonical-jump-tables
+// CHECK-NO-CFI-CANONICAL-JUMP-TABLES-NOT: -fsanitize-cfi-canonical-jump-tables
+
// RUN: %clang -target x86_64-linux-gnu -fsanitize=cfi -fsanitize-stats -flto -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-CFI-STATS
// CHECK-CFI-STATS: -fsanitize-stats
diff --git a/clang/test/Misc/pragma-attribute-supported-attributes-list.test b/clang/test/Misc/pragma-attribute-supported-attributes-list.test
index cc2d380..83b8b9f 100644
--- a/clang/test/Misc/pragma-attribute-supported-attributes-list.test
+++ b/clang/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -21,6 +21,7 @@
// CHECK-NEXT: Availability ((SubjectMatchRule_record, SubjectMatchRule_enum, SubjectMatchRule_enum_constant, SubjectMatchRule_field, SubjectMatchRule_function, SubjectMatchRule_namespace, SubjectMatchRule_objc_category, SubjectMatchRule_objc_implementation, SubjectMatchRule_objc_interface, SubjectMatchRule_objc_method, SubjectMatchRule_objc_property, SubjectMatchRule_objc_protocol, SubjectMatchRule_record, SubjectMatchRule_type_alias, SubjectMatchRule_variable))
// CHECK-NEXT: CFAuditedTransfer (SubjectMatchRule_function)
// CHECK-NEXT: CFConsumed (SubjectMatchRule_variable_is_parameter)
+// CHECK-NEXT: CFICanonicalJumpTable (SubjectMatchRule_function)
// CHECK-NEXT: CFUnknownTransfer (SubjectMatchRule_function)
// CHECK-NEXT: CPUDispatch (SubjectMatchRule_function)
// CHECK-NEXT: CPUSpecific (SubjectMatchRule_function)
diff --git a/clang/test/SemaCXX/attr-cfi-canonical-jump-table.cpp b/clang/test/SemaCXX/attr-cfi-canonical-jump-table.cpp
new file mode 100644
index 0000000..a53fbae
--- /dev/null
+++ b/clang/test/SemaCXX/attr-cfi-canonical-jump-table.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -fsyntax-only -verify %s
+
+__attribute__((cfi_canonical_jump_table)) void fdecl();
+
+__attribute__((cfi_canonical_jump_table)) void f() {}
+
+struct S {
+ __attribute__((cfi_canonical_jump_table)) void f() {}
+};
+
+__attribute__((cfi_canonical_jump_table)) int i; // expected-error {{'cfi_canonical_jump_table' attribute only applies to functions}}