[SanitizerCoverage] Make __start_/__stop_ symbols extern_weak

[MaskRay]

Summary

On ELF, we place the metadata sections (__sancov_guards, __sancov_cntrs,
__sancov_bools, __sancov_pcs in section groups (either comdat any or
comdat noduplicates).

With --gc-sections, LLD since D96753 and GNU ld -z start-stop-gc may garbage
collect such sections. If all __sancov_bools are discarded, LLD will error
error: undefined hidden symbol: __start___sancov_cntrs (other sections are similar).

% cat a.c
void discarded() {}
% clang -fsanitize-coverage=func,trace-pc-guard -fpic -fvisibility=hidden a.c -shared -fuse-ld=lld -Wl,--gc-sections
...
ld.lld: error: undefined hidden symbol: __start___sancov_guards
>>> referenced by a.c
>>>               /tmp/a-456662.o:(sancov.module_ctor_trace_pc_guard)

Use the extern_weak linkage (lowered to undefined weak symbols) to avoid the
undefined error.

[MaskRay]

drop accidental changes

[vitalybuka]

LGTM

[vitalybuka]

https://lab.llvm.org/buildbot/#/builders/127/builds/8015 fails like this

******************** TEST 'AddressSanitizer-x86_64-windows :: TestCases/Window
coverage-dll-stdio.cpp' FAILED ********************
Script:
--
: 'RUN: at line 4';   rm -rf C:\b\slave\sanitizer-windows\build\stage1\project
compiler-rt\test\asan\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dl
stdio.cpp.tmp && mkdir C:\b\slave\sanitizer-windows\build\stage1\projects\comp
er-rt\test\asan\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dll-stdi
cpp.tmp && cd C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\t
t\asan\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dll-stdio.cpp.tmp
: 'RUN: at line 5';      C:/b/slave/sanitizer-windows/build/stage1/./bin/clang
l.exe  -fsanitize=address -Wno-deprecated-declarations -WX -D_HAS_EXCEPTIONS=0
Zi     -fsanitize-coverage=func,trace-pc-guard -Od C:\b\slave\sanitizer-window
llvm-project\compiler-rt\test\asan\TestCases\Windows/dll_host.cpp -Fet.exe
: 'RUN: at line 6';      C:/b/slave/sanitizer-windows/build/stage1/./bin/clang
l.exe  -fsanitize=address -Wno-deprecated-declarations -WX -D_HAS_EXCEPTIONS=0
Zi     -fsanitize-coverage=func,trace-pc-guard -LD -Od C:\b\slave\sanitizer-wi
ows\llvm-project\compiler-rt\test\asan\TestCases\Windows\coverage-dll-stdio.cp
-Fet.dll
: 'RUN: at line 7';    ./t.exe t.dll 2>&1 | FileCheck C:\b\slave\sanitizer-win
ws\llvm-project\compiler-rt\test\asan\TestCases\Windows\coverage-dll-stdio.cpp
--
Exit Code: 1

Command Output (stdout):
--
$ ":" "RUN: at line 4"
$ "rm" "-rf" "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\t
t\asan\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dll-stdio.cpp.tmp
$ "mkdir" "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test
san\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dll-stdio.cpp.tmp"
$ "cd" "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\as
\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dll-stdio.cpp.tmp"
$ ":" "RUN: at line 5"
$ "C:/b/slave/sanitizer-windows/build/stage1/./bin/clang-cl.exe" "-fsanitize=a
ress" "-Wno-deprecated-declarations" "-WX" "-D_HAS_EXCEPTIONS=0" "-Zi" "-fsani
ze-coverage=func,trace-pc-guard" "-Od" "C:\b\slave\sanitizer-windows\llvm-proj
t\compiler-rt\test\asan\TestCases\Windows/dll_host.cpp" "-Fet.exe"
# command output:
   Creating library t.lib and object t.exp

$ ":" "RUN: at line 6"
$ "C:/b/slave/sanitizer-windows/build/stage1/./bin/clang-cl.exe" "-fsanitize=a
ress" "-Wno-deprecated-declarations" "-WX" "-D_HAS_EXCEPTIONS=0" "-Zi" "-fsani
ze-coverage=func,trace-pc-guard" "-LD" "-Od" "C:\b\slave\sanitizer-windows\llv
project\compiler-rt\test\asan\TestCases\Windows\coverage-dll-stdio.cpp" "-Fet.
l"
# command output:
   Creating library t.lib and object t.exp

$ ":" "RUN: at line 7"
$ "./t.exe" "t.dll"
note: command had no output on stdout or stderr
error: command failed with exit status: 1
$ "FileCheck" "C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\asan
estCases\Windows\coverage-dll-stdio.cpp"
# command stderr:
C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\asan\TestCases\Wind
s\coverage-dll-stdio.cpp:14:12: error: CHECK: expected string not found in inp

 // CHECK: hello world
           ^
<stdin>:1:1: note: scanning from here
Could not load DLL: t.dll (code: 1114)!
^

Input file: <stdin>
Check file: C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\asan\Te
Cases\Windows\coverage-dll-stdio.cpp

-dump-input=help explains the following input dump.

Input was:
<<<<<<
          1: Could not load DLL: t.dll (code: 1114)!
check:14     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
          2: =================================================================
check:14     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          3: ==6276==ERROR: AddressSanitizer: access-violation on unknown addr
s 0x7ffb669b458c (pc 0x7ffb669b458c bp 0x000000000002 sp 0x002d80a8f458 T0)
check:14     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          4: ==6276==The signal is caused by a UNKNOWN memory access.
check:14     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          5:  #0 0x7ffb669b458b (<unknown module>)
check:14     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          6:  #1 0x7ffb84aed596 (C:\windows\SYSTEM32\ntdll.dll+0x18001d596)
check:14     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          .
          .
          .
>>>>>>

error: command failed with exit status: 1

--

********************
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90..
********************
Failed Tests (1):
  AddressSanitizer-x86_64-windows :: TestCases/Windows/coverage-dll-stdio.cpp

reverting change helps

[MaskRay]

In D98903#2643589, @vitalybuka wrote:

https://lab.llvm.org/buildbot/#/builders/127/builds/8015 fails like this

******************** TEST 'AddressSanitizer-x86_64-windows :: TestCases/Window
coverage-dll-stdio.cpp' FAILED ********************
Script:
--
: 'RUN: at line 4';   rm -rf C:\b\slave\sanitizer-windows\build\stage1\project
compiler-rt\test\asan\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dl
stdio.cpp.tmp && mkdir C:\b\slave\sanitizer-windows\build\stage1\projects\comp
er-rt\test\asan\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dll-stdi
cpp.tmp && cd C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\t
t\asan\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dll-stdio.cpp.tmp
: 'RUN: at line 5';      C:/b/slave/sanitizer-windows/build/stage1/./bin/clang
l.exe  -fsanitize=address -Wno-deprecated-declarations -WX -D_HAS_EXCEPTIONS=0
Zi     -fsanitize-coverage=func,trace-pc-guard -Od C:\b\slave\sanitizer-window
llvm-project\compiler-rt\test\asan\TestCases\Windows/dll_host.cpp -Fet.exe
: 'RUN: at line 6';      C:/b/slave/sanitizer-windows/build/stage1/./bin/clang
l.exe  -fsanitize=address -Wno-deprecated-declarations -WX -D_HAS_EXCEPTIONS=0
Zi     -fsanitize-coverage=func,trace-pc-guard -LD -Od C:\b\slave\sanitizer-wi
ows\llvm-project\compiler-rt\test\asan\TestCases\Windows\coverage-dll-stdio.cp
-Fet.dll
: 'RUN: at line 7';    ./t.exe t.dll 2>&1 | FileCheck C:\b\slave\sanitizer-win
ws\llvm-project\compiler-rt\test\asan\TestCases\Windows\coverage-dll-stdio.cpp
--
Exit Code: 1

Command Output (stdout):
--
$ ":" "RUN: at line 4"
$ "rm" "-rf" "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\t
t\asan\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dll-stdio.cpp.tmp
$ "mkdir" "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test
san\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dll-stdio.cpp.tmp"
$ "cd" "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\as
\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dll-stdio.cpp.tmp"
$ ":" "RUN: at line 5"
$ "C:/b/slave/sanitizer-windows/build/stage1/./bin/clang-cl.exe" "-fsanitize=a
ress" "-Wno-deprecated-declarations" "-WX" "-D_HAS_EXCEPTIONS=0" "-Zi" "-fsani
ze-coverage=func,trace-pc-guard" "-Od" "C:\b\slave\sanitizer-windows\llvm-proj
t\compiler-rt\test\asan\TestCases\Windows/dll_host.cpp" "-Fet.exe"
# command output:
   Creating library t.lib and object t.exp

$ ":" "RUN: at line 6"
$ "C:/b/slave/sanitizer-windows/build/stage1/./bin/clang-cl.exe" "-fsanitize=a
ress" "-Wno-deprecated-declarations" "-WX" "-D_HAS_EXCEPTIONS=0" "-Zi" "-fsani
ze-coverage=func,trace-pc-guard" "-LD" "-Od" "C:\b\slave\sanitizer-windows\llv
project\compiler-rt\test\asan\TestCases\Windows\coverage-dll-stdio.cpp" "-Fet.
l"
# command output:
   Creating library t.lib and object t.exp

$ ":" "RUN: at line 7"
$ "./t.exe" "t.dll"
note: command had no output on stdout or stderr
error: command failed with exit status: 1
$ "FileCheck" "C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\asan
estCases\Windows\coverage-dll-stdio.cpp"
# command stderr:
C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\asan\TestCases\Wind
s\coverage-dll-stdio.cpp:14:12: error: CHECK: expected string not found in inp

 // CHECK: hello world
           ^
<stdin>:1:1: note: scanning from here
Could not load DLL: t.dll (code: 1114)!
^

Input file: <stdin>
Check file: C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\asan\Te
Cases\Windows\coverage-dll-stdio.cpp

-dump-input=help explains the following input dump.

Input was:
<<<<<<
          1: Could not load DLL: t.dll (code: 1114)!
check:14     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
          2: =================================================================
check:14     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          3: ==6276==ERROR: AddressSanitizer: access-violation on unknown addr
s 0x7ffb669b458c (pc 0x7ffb669b458c bp 0x000000000002 sp 0x002d80a8f458 T0)
check:14     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          4: ==6276==The signal is caused by a UNKNOWN memory access.
check:14     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          5:  #0 0x7ffb669b458b (<unknown module>)
check:14     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          6:  #1 0x7ffb84aed596 (C:\windows\SYSTEM32\ntdll.dll+0x18001d596)
check:14     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          .
          .
          .
>>>>>>

error: command failed with exit status: 1

--

********************
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90..
********************
Failed Tests (1):
  AddressSanitizer-x86_64-windows :: TestCases/Windows/coverage-dll-stdio.cpp

reverting change helps

How about hacking Windows to not use extern_weak?

[vitalybuka]

LGTM, I assume problem the patch is solving is not an issues on Windows?

In D98903#2643603, @MaskRay wrote:

In D98903#2643589, @vitalybuka wrote:

https://lab.llvm.org/buildbot/#/builders/127/builds/8015 fails like this

******************** TEST 'AddressSanitizer-x86_64-windows :: TestCases/Window
coverage-dll-stdio.cpp' FAILED ********************
Script:
--
: 'RUN: at line 4';   rm -rf C:\b\slave\sanitizer-windows\build\stage1\project
compiler-rt\test\asan\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dl
stdio.cpp.tmp && mkdir C:\b\slave\sanitizer-windows\build\stage1\projects\comp
er-rt\test\asan\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dll-stdi
cpp.tmp && cd C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\t
t\asan\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dll-stdio.cpp.tmp
: 'RUN: at line 5';      C:/b/slave/sanitizer-windows/build/stage1/./bin/clang
l.exe  -fsanitize=address -Wno-deprecated-declarations -WX -D_HAS_EXCEPTIONS=0
Zi     -fsanitize-coverage=func,trace-pc-guard -Od C:\b\slave\sanitizer-window
llvm-project\compiler-rt\test\asan\TestCases\Windows/dll_host.cpp -Fet.exe
: 'RUN: at line 6';      C:/b/slave/sanitizer-windows/build/stage1/./bin/clang
l.exe  -fsanitize=address -Wno-deprecated-declarations -WX -D_HAS_EXCEPTIONS=0
Zi     -fsanitize-coverage=func,trace-pc-guard -LD -Od C:\b\slave\sanitizer-wi
ows\llvm-project\compiler-rt\test\asan\TestCases\Windows\coverage-dll-stdio.cp
-Fet.dll
: 'RUN: at line 7';    ./t.exe t.dll 2>&1 | FileCheck C:\b\slave\sanitizer-win
ws\llvm-project\compiler-rt\test\asan\TestCases\Windows\coverage-dll-stdio.cpp
--
Exit Code: 1

Command Output (stdout):
--
$ ":" "RUN: at line 4"
$ "rm" "-rf" "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\t
t\asan\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dll-stdio.cpp.tmp
$ "mkdir" "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test
san\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dll-stdio.cpp.tmp"
$ "cd" "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\as
\X86_64WindowsConfig\TestCases\Windows\Output\coverage-dll-stdio.cpp.tmp"
$ ":" "RUN: at line 5"
$ "C:/b/slave/sanitizer-windows/build/stage1/./bin/clang-cl.exe" "-fsanitize=a
ress" "-Wno-deprecated-declarations" "-WX" "-D_HAS_EXCEPTIONS=0" "-Zi" "-fsani
ze-coverage=func,trace-pc-guard" "-Od" "C:\b\slave\sanitizer-windows\llvm-proj
t\compiler-rt\test\asan\TestCases\Windows/dll_host.cpp" "-Fet.exe"
# command output:
   Creating library t.lib and object t.exp

$ ":" "RUN: at line 6"
$ "C:/b/slave/sanitizer-windows/build/stage1/./bin/clang-cl.exe" "-fsanitize=a
ress" "-Wno-deprecated-declarations" "-WX" "-D_HAS_EXCEPTIONS=0" "-Zi" "-fsani
ze-coverage=func,trace-pc-guard" "-LD" "-Od" "C:\b\slave\sanitizer-windows\llv
project\compiler-rt\test\asan\TestCases\Windows\coverage-dll-stdio.cpp" "-Fet.
l"
# command output:
   Creating library t.lib and object t.exp

$ ":" "RUN: at line 7"
$ "./t.exe" "t.dll"
note: command had no output on stdout or stderr
error: command failed with exit status: 1
$ "FileCheck" "C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\asan
estCases\Windows\coverage-dll-stdio.cpp"
# command stderr:
C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\asan\TestCases\Wind
s\coverage-dll-stdio.cpp:14:12: error: CHECK: expected string not found in inp

 // CHECK: hello world
           ^
<stdin>:1:1: note: scanning from here
Could not load DLL: t.dll (code: 1114)!
^

Input file: <stdin>
Check file: C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\asan\Te
Cases\Windows\coverage-dll-stdio.cpp

-dump-input=help explains the following input dump.

Input was:
<<<<<<
          1: Could not load DLL: t.dll (code: 1114)!
check:14     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
          2: =================================================================
check:14     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          3: ==6276==ERROR: AddressSanitizer: access-violation on unknown addr
s 0x7ffb669b458c (pc 0x7ffb669b458c bp 0x000000000002 sp 0x002d80a8f458 T0)
check:14     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          4: ==6276==The signal is caused by a UNKNOWN memory access.
check:14     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          5:  #0 0x7ffb669b458b (<unknown module>)
check:14     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          6:  #1 0x7ffb84aed596 (C:\windows\SYSTEM32\ntdll.dll+0x18001d596)
check:14     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          .
          .
          .
>>>>>>

error: command failed with exit status: 1

--

********************
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90..
********************
Failed Tests (1):
  AddressSanitizer-x86_64-windows :: TestCases/Windows/coverage-dll-stdio.cpp

reverting change helps

How about hacking Windows to not use extern_weak?

[aeubanks]

In D98903#2643608, @vitalybuka wrote:

LGTM, I assume problem the patch is solving is not an issues on Windows?

It was a Linux issue.

[MaskRay]

Fixed by 3c81822ec5d2375d243ef2d43468807aa96383ec. I used this comment:

+ Windows defines the start/stop symbols in compiler-rt so no need for
+ ExternalWeak.

(See lib/sanitizer_common/sanitizer_coverage_win_sections.cpp)

The comment could be improved if I knew why the test (https://lab.llvm.org/buildbot/#/builders/127/builds/8015) failed... @rnk

[vitalybuka]

Thanks!

llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp

PreservedAnalyses ModuleSanitizerCoveragePass::run(Module &M,
   if (ModuleSancov.instrumentModule(M, DTCallback, PDTCallback))
     return PreservedAnalyses::none();
   return PreservedAnalyses::all();
 }
 
 std::pair<Value *, Value *>
 ModuleSanitizerCoverage::CreateSecStartEnd(Module &M, const char *Section,
                                            Type *Ty) {
+  // Use ExternalWeak so that if all sections are discarded due to section
+  // garbage collection, the linker will not report undefined symbol errors.
   GlobalVariable *SecStart = new GlobalVariable(
-      M, Ty->getPointerElementType(), false, GlobalVariable::ExternalLinkage,
-      nullptr, getSectionStart(Section));
+      M, Ty->getPointerElementType(), false,
+      GlobalVariable::ExternalWeakLinkage, nullptr, getSectionStart(Section));
   SecStart->setVisibility(GlobalValue::HiddenVisibility);
   GlobalVariable *SecEnd = new GlobalVariable(
-      M, Ty->getPointerElementType(), false, GlobalVariable::ExternalLinkage,
-      nullptr, getSectionEnd(Section));
+      M, Ty->getPointerElementType(), false,
+      GlobalVariable::ExternalWeakLinkage, nullptr, getSectionEnd(Section));
   SecEnd->setVisibility(GlobalValue::HiddenVisibility);
   IRBuilder<> IRB(M.getContext());
   if (!TargetTriple.isOSBinFormatCOFF())
     return std::make_pair(SecStart, SecEnd);
 
   // Account for the fact that on windows-msvc __start_* symbols actually
   // point to a uint64_t before the start of the array.
   auto SecStartI8Ptr = IRB.CreatePointerCast(SecStart, Int8PtrTy);

llvm/test/Instrumentation/SanitizerCoverage/inline-8bit-counters.ll

 ; Test -sanitizer-coverage-inline-8bit-counters=1
 ; RUN: opt < %s -sancov -sanitizer-coverage-level=1 -sanitizer-coverage-inline-8bit-counters=1  -S -enable-new-pm=0 | FileCheck %s
 ; RUN: opt < %s -passes='module(sancov-module)' -sanitizer-coverage-level=1 -sanitizer-coverage-inline-8bit-counters=1  -S | FileCheck %s
 
+; CHECK:      @__sancov_gen_ = private global [1 x i8] zeroinitializer, section "__sancov_cntrs", comdat($foo), align 1
+; CHECK:      @__start___sancov_cntrs = extern_weak hidden global i8
+; CHECK-NEXT: @__stop___sancov_cntrs = extern_weak hidden global i8
+
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
 target triple = "x86_64-unknown-linux-gnu"
 define void @foo() {
 entry:
-; CHECK: section "__sancov_cntrs", comdat($foo), align 1
 ; CHECK:  %0 = load i8, i8* getelementptr inbounds ([1 x i8], [1 x i8]* @__sancov_gen_, i64 0, i64 0), align 1, !nosanitize
 ; CHECK:  %1 = add i8 %0, 1
 ; CHECK:  store i8 %1, i8* getelementptr inbounds ([1 x i8], [1 x i8]* @__sancov_gen_, i64 0, i64 0), align 1, !nosanitize
   ret void
 }
 ; CHECK: call void @__sanitizer_cov_8bit_counters_init(i8* @__start___sancov_cntrs, i8* @__stop___sancov_cntrs)

llvm/test/Instrumentation/SanitizerCoverage/inline-bool-flag.ll

 ; Test -sanitizer-coverage-inline-bool-flag=1
 ; RUN: opt < %s -sancov -sanitizer-coverage-level=1 -sanitizer-coverage-inline-bool-flag=1  -S -enable-new-pm=0 | FileCheck %s
 ; RUN: opt < %s -passes='module(sancov-module)' -sanitizer-coverage-level=1 -sanitizer-coverage-inline-bool-flag=1  -S | FileCheck %s
 
 ; CHECK:      $foo = comdat noduplicates
 ; CHECK:      @__sancov_gen_ = private global [1 x i1] zeroinitializer, section "__sancov_bools", comdat($foo), align 1{{$}}
+; CHECK:      @__start___sancov_bools = extern_weak hidden global i1
+; CHECK-NEXT: @__stop___sancov_bools = extern_weak hidden global i1
 ; CHECK-NOT:  @llvm.used =
 ; CHECK:      @llvm.compiler.used = appending global [1 x i8*] [i8* bitcast ([1 x i1]* @__sancov_gen_ to i8*)], section "llvm.metadata"
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
 target triple = "x86_64-unknown-linux-gnu"
 define void @foo() {
 ; CHECK-LABEL: @foo(
 ; CHECK-NEXT:  entry:

llvm/test/Instrumentation/SanitizerCoverage/pc-table.ll

entry:
   store i32 0, i32* %a, align 4
   br label %if.end
 
   if.end:                                           ; preds = %entry, %if.then
   ret void
 }
 
 ; CHECK: private constant [6 x i64*] [{{.*}}@foo{{.*}}blockaddress{{.*}}blockaddress{{.*}}], section "__sancov_pcs", comdat($foo), align 8
+; CHECK:      @__start___sancov_pcs = extern_weak hidden global i64
+; CHECK-NEXT: @__stop___sancov_pcs = extern_weak hidden global i64
 ; CHECK: define internal void @sancov.module_ctor
 ; CHECK: call void @__sanitizer_cov
 ; CHECK: call void @__sanitizer_cov_pcs_init