[asan] Default to -asan-use-private-alias=1

[MaskRay]

Summary

This enables private aliases on ELF/Mach-O/WebAssembly platforms even if
-fsanitize-address-use-odr-indicator is not specified.
Note that GCC also uses private aliases.

Pros: the following issues are fixed

• Bogus The following global variable is not properly aligned. error for interposed global variables.

(PR37545 (this patch should allow us to restore D46665) and https://github.com/google/sanitizers/issues/1017)

Global variables of non-hasExactDefinition() linkages (i.e.
linkonce/linkonce_odr/weak/weak_odr/common/external_weak) are not instrumented.
If an instrumented variable gets interposed to an uninstrumented variable due to symbol
interposition (e.g. in PR37545, _ZTS1A in foo.so is resolved to _ZTS1A in the
executable), there may be a bogus error.

With private aliases, the register code will not resolve to a definition in another module,
and thus prevent the issue.

• https://github.com/google/sanitizers/issues/398

Similar to the above, but about an instrumented global variable gets interposed
to an uninstrumented global variable (not using address sanitizer) in another
module.

Cons:

• vtable ODR issues due to interposition are no longer detectable, e.g. compiler-rt/test/asan/TestCases/Linux/odr_vtable.cpp

• ODR issues due to mixed instrumented and non-instrumented globals (interposition) are no longer detectable, e.g. compiler-rt/test/asan/TestCases/Linux/odr_c_test.c

• Can't catch overflows in globals relocated by R_*_COPY

(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68016)
This affects -fno-pic and -fpie -mpie-copy-relocations.
However, -fpie (without -mpie-copy-relocations) produced code can still
catch the overflow.

// foo.so
int f[5] = {1};
// a.out
extern int f[5]; int main() { return f[5]; }

• For ELF, minor object file size increases due to extra STT_SECTION

symbols in the symbol table (private aliases replace some relocations
referencing global symbols with .L symbols which are typically lower to
STT_SECTION symbols). The linked image usually has no size difference.

[vitalybuka]

I guess another cons was binary size increase? Would you like to run large scale testing on internal Google code?

[MaskRay]

In D92078#2427100, @vitalybuka wrote:

I guess another cons was binary size increase? Would you like to run large scale testing on internal Google code?

Did a large scale testing in internal Google code - tests passed.

For a linked shared object/executable, there is no size difference (checked with an asan clang). In object files, there are minimal differences:

% diff -U1 a.s b.s
--- a.s 2020-12-02 10:33:09.222518415 -0800
+++ b.s 2020-12-02 10:33:13.082528586 -0800
@@ -76,3 +76,3 @@
 __unnamed_1:
-       .quad   _ZN3foo1GE
+       .quad   .L__unnamed_2
        .quad   4                               # 0x4
@@ -92,2 +92,3 @@
        .quad   asan.module_dtor
+.set .L__unnamed_2, _ZN3foo1GE
        .ident  "clang version 12.0.0"
@@ -104 +105,2 @@
        .addrsig_sym __unnamed_1
+       .addrsig_sym .L__unnamed_2

• Some global symbol referenced relocations are converted to reference local symbols. Using private aliases can cause some extra STT_SECTION symbols (for .data/.bss). The cost should be acceptable.
• .llvm_addrsig: it may have additional entries for the extra STT_SECTION symbols (the encoding uses LEB128, so the increase is like one byte for each extra symbol)

[MaskRay]

Fix two clang/test/CodeGen tests

[vitalybuka]

https://reviews.llvm.org/D55156
So with this patch no code increase but we lose ODR checks.
To preserve checks we need -fsanitize-address-use-odr-indicator but then binary size increase.

[vitalybuka]

alias change is LGTM, we can try to figure-out how to roll out -fsanitize-address-use-odr-indicator

compiler-rt/test/asan/TestCases/Linux/odr-vtable.cpp

16

now we don't test default behavior
can you add CHECKs for alias=1 as well?
same below

[MaskRay]

Improve odr-vtable.cpp

[vitalybuka]

compiler-rt/test/asan/TestCases/Linux/odr-vtable.cpp

15–16

Is this going to work?

16

It was more about llvm/test/Instrumentation test

You just flipped to asan-use-private-alias=0 so we do not test =1. it was an issue before but now as with that as default we need to test it.

llvm/test/Instrumentation/AddressSanitizer/global_metadata.ll

1–4 ↗

(On Diff #309058)

llvm/test/Instrumentation/AddressSanitizer/global_metadata_darwin.ll

4–6 ↗

(On Diff #309058)

llvm/test/Instrumentation/AddressSanitizer/local_alias.ll

2–13

I didn't update FileCheck here

llvm/test/Instrumentation/AddressSanitizer/odr-check-ignore.ll

1–2 ↗

(On Diff #309058)

[MaskRay]

Pre-committed test improvement in 190b4374c00a9cf090ea73f9eddf3d8f71b11ec8
Rebase

compiler-rt/test/asan/TestCases/Linux/odr-vtable.cpp

15–16

Yes. -asan-use-odr-indicator=1 adds a named global symbol which can detect such issues.

[vitalybuka]

I've chatted about that with @kcc and @eugenis . It seems the problem the patch is trying to solve is less important than regressions. Even with the current state when rare false ODR reports are possible it still useful.
It would be nice with -fsanitize-address-use-odr-indicator, but someone will need to figure-out what to do with few users broken by binary size increase.

[vitalybuka]

I assume we are not moving forward with this patch?

[MaskRay]

Obsoleted by D137227

clang/test/CodeGen/asan-globals-odr.cpp

-// RUN: %clang_cc1 -fsanitize=address -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefixes=CHECK,INDICATOR0,GLOB_VAR,ALIAS0
+// RUN: %clang_cc1 -fsanitize=address -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefixes=CHECK,INDICATOR0,GLOB_ALIAS,ALIAS1
 // RUN: %clang_cc1 -fsanitize=address -fsanitize-address-use-odr-indicator -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefixes=CHECK,INDICATOR1,GLOB_ALIAS_INDICATOR,ALIAS1
-// RUN: %clang_cc1 -fsanitize=address -fno-sanitize-address-use-odr-indicator -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefixes=CHECK,INDICATOR0,GLOB_VAR,ALIAS0
+// RUN: %clang_cc1 -fsanitize=address -fno-sanitize-address-use-odr-indicator -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefixes=CHECK,INDICATOR0,GLOB_ALIAS,ALIAS1
 // RUN: %clang_cc1 -fsanitize=address -fno-sanitize-address-use-odr-indicator -fsanitize-address-use-odr-indicator -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefixes=CHECK,INDICATOR1,GLOB_ALIAS_INDICATOR,ALIAS1
-// RUN: %clang_cc1 -fsanitize=address -fsanitize-address-use-odr-indicator -fno-sanitize-address-use-odr-indicator -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefixes=CHECK,INDICATOR0,GLOB_VAR,ALIAS0
+// RUN: %clang_cc1 -fsanitize=address -fsanitize-address-use-odr-indicator -fno-sanitize-address-use-odr-indicator -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefixes=CHECK,INDICATOR0,GLOB_ALIAS,ALIAS1
 
 // No alias on Windows but indicators should work.
 // RUN: %clang_cc1 -fsanitize=address -emit-llvm -o - -triple x86_64-windows-msvc %s | FileCheck %s --check-prefixes=CHECK,GLOB_VAR,ALIAS0
 // RUN: %clang_cc1 -fsanitize=address -fsanitize-address-use-odr-indicator -emit-llvm -o - -triple x86_64-windows-msvc %s | FileCheck %s --check-prefixes=CHECK,INDICATOR1,GLOB_VAR_INDICATOR,ALIAS0
 
 int global;
 
 int main() {

clang/test/CodeGen/asan-static-odr.cpp

-// RUN: %clang_cc1 -fsanitize=address -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s
+// RUN: %clang_cc1 -fsanitize=address -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefixes=CHECK,ELF
 
 // No alias on Windows but indicators should work.
-// RUN: %clang_cc1 -fsanitize=address -emit-llvm -o - -triple x86_64-windows-msvc %s | FileCheck %s
+// RUN: %clang_cc1 -fsanitize=address -emit-llvm -o - -triple x86_64-windows-msvc %s | FileCheck %s --check-prefixes=CHECK,COFF
 
 static int global;
 
 int main() {
   return global;
 }
 
 // CHECK-NOT: __odr_asan_gen
 // CHECK-NOT: private alias
 // CHECK: [[VAR:@.*global.*]] ={{.*}} global { i32, [60 x i8] } zeroinitializer, align 32
-// CHECK: @0 = internal global {{.*}} [[VAR]] to i64), {{.*}}, i64 -1 }]
+// ELF:   @0 = internal global {{.*}} @1 to i64), {{.*}}, i64 -1 }]
+// ELF:   @1 = private alias { i32, [60 x i8] }, { i32, [60 x i8] }* [[VAR]]
+// WIN:   @0 = internal global {{.*}} [[VAR]] to i64), {{.*}}, i64 -1 }]
+// WIN-NOT: private alias
 // CHECK: call void @__asan_register_globals(i64 ptrtoint ([1 x { i64, i64, i64, i64, i64, i64, i64, i64 }]* @0 to i64), i64 1)
 // CHECK: call void @__asan_unregister_globals(i64 ptrtoint ([1 x { i64, i64, i64, i64, i64, i64, i64, i64 }]* @0 to i64), i64 1)

compiler-rt/test/asan/TestCases/Linux/odr-violation.cpp

 // FIXME: https://code.google.com/p/address-sanitizer/issues/detail?id=316
 // XFAIL: android
 // Fails with debug checks: https://bugs.llvm.org/show_bug.cgi?id=46862
 // XFAIL: !compiler-rt-optimized && !riscv64
 //
 // We use fast_unwind_on_malloc=0 to have full unwinding even w/o frame
 // pointers. This setting is not on by default because it's too expensive.
 //
+// Note, -asan-use-private-alias=1 -asan-use-odr-indicator=0 is the default.
+//
 // Different size: detect a bug if detect_odr_violation>=1
-// RUN: %clangxx_asan -DBUILD_SO=1 -fPIC -shared %s -o %dynamiclib
-// RUN: %clangxx_asan %s %ld_flags_rpath_exe -o %t-ODR-EXE
+// RUN: %clangxx_asan -DBUILD_SO=1 -fPIC -shared -mllvm -asan-use-private-alias=0 %s -o %dynamiclib
+// RUN: %clangxx_asan -mllvm -asan-use-private-alias=0 %s %ld_flags_rpath_exe -o %t-ODR-EXE
 // RUN: %env_asan_opts=fast_unwind_on_malloc=0:detect_odr_violation=1 not %run %t-ODR-EXE 2>&1 | FileCheck %s
 // RUN: %env_asan_opts=fast_unwind_on_malloc=0:detect_odr_violation=2 not %run %t-ODR-EXE 2>&1 | FileCheck %s
 // RUN: %env_asan_opts=fast_unwind_on_malloc=0:detect_odr_violation=0     %run %t-ODR-EXE 2>&1 | FileCheck %s --check-prefix=DISABLED
 // RUN: %env_asan_opts=fast_unwind_on_malloc=0                        not %run %t-ODR-EXE 2>&1 | FileCheck %s
 //
 // Same size: report a bug only if detect_odr_violation>=2.
-// RUN: %clangxx_asan -DBUILD_SO=1 -fPIC -shared %s -o %dynamiclib -DSZ=100
+// RUN: %clangxx_asan -DBUILD_SO=1 -fPIC -shared -mllvm -asan-use-private-alias=0 %s -o %dynamiclib -DSZ=100
 // RUN: %env_asan_opts=fast_unwind_on_malloc=0:detect_odr_violation=1     %run %t-ODR-EXE 2>&1 | FileCheck %s --check-prefix=DISABLED
 // RUN: %env_asan_opts=fast_unwind_on_malloc=0:detect_odr_violation=2 not %run %t-ODR-EXE 2>&1 | FileCheck %s
 // RUN: %env_asan_opts=fast_unwind_on_malloc=0                        not %run %t-ODR-EXE 2>&1 | FileCheck %s
 // RUN: echo "odr_violation:foo::ZZZ" > %t.supp
 // RUN: %env_asan_opts=fast_unwind_on_malloc=0:detect_odr_violation=2:suppressions=%t.supp  not %run %t-ODR-EXE 2>&1 | FileCheck %s
 // RUN: echo "odr_violation:foo::G" > %t.supp
 // RUN: %env_asan_opts=fast_unwind_on_malloc=0:detect_odr_violation=2:suppressions=%t.supp      %run %t-ODR-EXE 2>&1 | FileCheck %s --check-prefix=DISABLED
 // RUN: rm -f %t.supp
 //
 // Use private aliases for global variables without indicator symbol.
-// RUN: %clangxx_asan -DBUILD_SO=1 -fPIC -shared -mllvm -asan-use-private-alias %s -o %dynamiclib -DSZ=100
+// RUN: %clangxx_asan -DBUILD_SO=1 -fPIC -shared %s -o %dynamiclib -DSZ=100
 // RUN: %clangxx_asan -mllvm -asan-use-private-alias %s %ld_flags_rpath_exe -o %t-ODR-EXE
 // RUN: %env_asan_opts=fast_unwind_on_malloc=0 %run %t-ODR-EXE 2>&1 | FileCheck %s --check-prefix=DISABLED
 
 // Use private aliases for global variables: use indicator symbol to detect ODR violation.
-// RUN: %clangxx_asan -DBUILD_SO=1 -fPIC -shared -mllvm -asan-use-private-alias -mllvm -asan-use-odr-indicator  %s -o %dynamiclib -DSZ=100
+// RUN: %clangxx_asan -DBUILD_SO=1 -fPIC -shared -mllvm -asan-use-odr-indicator %s -o %dynamiclib -DSZ=100
 // RUN: %clangxx_asan -mllvm -asan-use-private-alias -mllvm -asan-use-odr-indicator %s %ld_flags_rpath_exe -o %t-ODR-EXE
 // RUN: %env_asan_opts=fast_unwind_on_malloc=0 not %run %t-ODR-EXE 2>&1 | FileCheck %s
 
 // Same as above but with clang switches.
 // RUN: %clangxx_asan -DBUILD_SO=1 -fPIC -shared -fsanitize-address-use-odr-indicator %s -o %dynamiclib -DSZ=100
 // RUN: %clangxx_asan -fsanitize-address-use-odr-indicator %s %ld_flags_rpath_exe -o %t-ODR-EXE
 // RUN: %env_asan_opts=fast_unwind_on_malloc=0 not %run %t-ODR-EXE 2>&1 | FileCheck %s
 

compiler-rt/test/asan/TestCases/Linux/odr-vtable.cpp

 // Fails with debug checks: https://bugs.llvm.org/show_bug.cgi?id=46862
 // XFAIL: !compiler-rt-optimized && !riscv64
 
 /// Not using private alias or enabling ODR indicator can detect ODR issues.
 // RUN: %clangxx_asan -fno-rtti -DBUILD_SO1 -fPIC -shared -mllvm -asan-use-private-alias=0 %s -o %dynamiclib1
 // RUN: %clangxx_asan -fno-rtti -DBUILD_SO2 -fPIC -shared -mllvm -asan-use-private-alias=0 %s -o %dynamiclib2
 // RUN: %env_asan_opts=fast_unwind_on_malloc=0:detect_odr_violation=2 not %run %t 2>&1 | FileCheck %s
 
 // RUN: %clangxx_asan -fno-rtti -DBUILD_SO1 -fPIC -shared -mllvm -asan-use-odr-indicator=1 %s -o %dynamiclib1
 // RUN: %clangxx_asan -fno-rtti -DBUILD_SO2 -fPIC -shared -mllvm -asan-use-odr-indicator=1 %s -o %dynamiclib2
 // RUN: %env_asan_opts=fast_unwind_on_malloc=0:detect_odr_violation=2 not %run %t 2>&1 | FileCheck %s
 
-/// By default we can detect ODR issues in vtables.
+/// By default we cannot detect ODR issues in vtables.
 // RUN: %clangxx_asan -fno-rtti -DBUILD_SO1 -fPIC -shared %s -o %dynamiclib1
 // RUN: %clangxx_asan -fno-rtti -DBUILD_SO2 -fPIC -shared %s -o %dynamiclib2
 // RUN: %clangxx_asan -fno-rtti %s %ld_flags_rpath_exe1 %ld_flags_rpath_exe2 -o %t
-// RUN: %env_asan_opts=fast_unwind_on_malloc=0:detect_odr_violation=2 not %run %t 2>&1 | FileCheck %s
+// RUN: %env_asan_opts=fast_unwind_on_malloc=0:detect_odr_violation=2 %run %t 2>&1 | count 0
 
 struct XYZ {
   virtual void foo();
 };
 
 #if defined(BUILD_SO1)
 
 void XYZ::foo() {}

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

 static cl::opt<uint32_t> ClForceExperiment(
     "asan-force-experiment",
     cl::desc("Force optimization experiment (for testing)"), cl::Hidden,
     cl::init(0));
 
 static cl::opt<bool>
     ClUsePrivateAlias("asan-use-private-alias",
                       cl::desc("Use private aliases for global variables"),
-                      cl::Hidden, cl::init(false));
+                      cl::Hidden, cl::init(true));
 
 static cl::opt<bool>
     ClUseOdrIndicator("asan-use-odr-indicator",
                       cl::desc("Use odr indicators to improve ODR reporting"),
                       cl::Hidden, cl::init(false));
 
 static cl::opt<bool>
     ClUseGlobalsGC("asan-globals-live-support",

llvm/test/Instrumentation/AddressSanitizer/local_alias.ll

 ; Defaults
-; RUN: opt < %s -asan -asan-module -enable-new-pm=0 -S | FileCheck %s --check-prefixes=CHECK-NOALIAS,CHECK-NOINDICATOR
-; RUN: opt < %s -passes='asan-pipeline' -S | FileCheck %s --check-prefixes=CHECK-NOALIAS,CHECK-NOINDICATOR
+; RUN: opt < %s -asan -asan-module -enable-new-pm=0 -S | FileCheck %s --check-prefixes=CHECK-ALIAS,CHECK-NOINDICATOR
+; RUN: opt < %s -passes='asan-pipeline' -S | FileCheck %s --check-prefixes=CHECK-ALIAS,CHECK-NOINDICATOR
 
 ; {newPM,legacyPM} x {alias0,alias1} x {odr0,odr1}
 ; RUN: opt < %s -asan -asan-module -enable-new-pm=0 -asan-use-private-alias=0 -asan-use-odr-indicator=0 -S | FileCheck %s --check-prefixes=CHECK-NOALIAS,CHECK-NOINDICATOR
 ; RUN: opt < %s -passes='asan-pipeline'             -asan-use-private-alias=0 -asan-use-odr-indicator=0 -S | FileCheck %s --check-prefixes=CHECK-NOALIAS,CHECK-NOINDICATOR
 ; RUN: opt < %s -asan -asan-module -enable-new-pm=0 -asan-use-private-alias=1 -asan-use-odr-indicator=0 -S | FileCheck %s --check-prefixes=CHECK-ALIAS,CHECK-NOINDICATOR
 ; RUN: opt < %s -passes='asan-pipeline'             -asan-use-private-alias=1 -asan-use-odr-indicator=0 -S | FileCheck %s --check-prefixes=CHECK-ALIAS,CHECK-NOINDICATOR
 ; RUN: opt < %s -asan -asan-module -enable-new-pm=0 -asan-use-private-alias=0 -asan-use-odr-indicator=1 -S | FileCheck %s --check-prefixes=CHECK-NOALIAS,CHECK-INDICATOR
 ; RUN: opt < %s -passes='asan-pipeline'             -asan-use-private-alias=0 -asan-use-odr-indicator=1 -S | FileCheck %s --check-prefixes=CHECK-NOALIAS,CHECK-INDICATOR
 ; RUN: opt < %s -asan -asan-module -enable-new-pm=0 -asan-use-private-alias=1 -asan-use-odr-indicator=1 -S | FileCheck %s --check-prefixes=CHECK-ALIAS,CHECK-INDICATOR
 ; RUN: opt < %s -passes='asan-pipeline'             -asan-use-private-alias=1 -asan-use-odr-indicator=1 -S | FileCheck %s --check-prefixes=CHECK-ALIAS,CHECK-INDICATOR
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 @a = dso_local global [2 x i32] zeroinitializer, align 4
 @b = private global [2 x i32] zeroinitializer, align 4
 @c = internal global [2 x i32] zeroinitializer, align 4
 @d = unnamed_addr global [2 x i32] zeroinitializer, align 4