Commit Graph

665 Commits

Author SHA1 Message Date
Matt Morehouse 7e042bb1d1 [libFuzzer] Port to Windows
Summary:
Port libFuzzer to windows-msvc.
This patch allows libFuzzer targets to be built and run on Windows, using -fsanitize=fuzzer and/or fsanitize=fuzzer-no-link. It allows these forms of coverage instrumentation to work on Windows as well.
It does not fix all issues, such as those with -fsanitize-coverage=stack-depth, which is not usable on Windows as of this patch.
It also does not fix any libFuzzer integration tests. Nearly all of them fail to compile, fixing them will come in a later patch, so libFuzzer tests are disabled on Windows until them.

Patch By: metzman

Reviewers: morehouse, rnk

Reviewed By: morehouse, rnk

Subscribers: #sanitizers, delcypher, morehouse, kcc, eraman

Differential Revision: https://reviews.llvm.org/D51022

llvm-svn: 341082
2018-08-30 15:54:44 +00:00
Matt Morehouse cf311cfc20 Revert "[libFuzzer] Port to Windows"
This reverts r340949 due to bot breakage again.

llvm-svn: 340954
2018-08-29 18:40:41 +00:00
Matt Morehouse 245ebd71ef [libFuzzer] Port to Windows
Summary:
Port libFuzzer to windows-msvc.
This patch allows libFuzzer targets to be built and run on Windows, using -fsanitize=fuzzer and/or fsanitize=fuzzer-no-link. It allows these forms of coverage instrumentation to work on Windows as well.
It does not fix all issues, such as those with -fsanitize-coverage=stack-depth, which is not usable on Windows as of this patch.
It also does not fix any libFuzzer integration tests. Nearly all of them fail to compile, fixing them will come in a later patch, so libFuzzer tests are disabled on Windows until them.

Reviewers: morehouse, rnk

Reviewed By: morehouse, rnk

Subscribers: #sanitizers, delcypher, morehouse, kcc, eraman

Differential Revision: https://reviews.llvm.org/D51022

llvm-svn: 340949
2018-08-29 18:08:34 +00:00
Matt Morehouse bab8556f01 Revert "[libFuzzer] Port to Windows"
This reverts commit r340860 due to failing tests.

llvm-svn: 340867
2018-08-28 19:07:24 +00:00
Matt Morehouse c6fff3b6f5 [libFuzzer] Port to Windows
Summary:
Port libFuzzer to windows-msvc.
This patch allows libFuzzer targets to be built and run on Windows, using -fsanitize=fuzzer and/or fsanitize=fuzzer-no-link. It allows these forms of coverage instrumentation to work on Windows as well.
It does not fix all issues, such as those with -fsanitize-coverage=stack-depth, which is not usable on Windows as of this patch.
It also does not fix any libFuzzer integration tests. Nearly all of them fail to compile, fixing them will come in a later patch, so libFuzzer tests are disabled on Windows until them.

Patch By: metzman

Reviewers: morehouse, rnk

Reviewed By: morehouse, rnk

Subscribers: morehouse, kcc, eraman

Differential Revision: https://reviews.llvm.org/D51022

llvm-svn: 340860
2018-08-28 18:34:32 +00:00
Reid Kleckner 1d432ae284 Fix global_metadata_external_comdat.ll test
llvm-svn: 340240
2018-08-21 00:03:21 +00:00
Reid Kleckner 85a8c12db8 Re-land r334313 "[asan] Instrument comdat globals on COFF targets"
If we can use comdats, then we can make it so that the global metadata
is thrown away if the prevailing definition of the global was
uninstrumented. I have only tested this on COFF targets, but in theory,
there is no reason that we cannot also do this for ELF.

This will allow us to re-enable string merging with ASan on Windows,
reducing the binary size cost of ASan on Windows.

I tested this change with ASan+PGO, and I fixed an issue with the
__llvm_profile_raw_version symbol. With the old version of my patch, we
would attempt to instrument that symbol on ELF because it had a comdat
with external linkage. If we had been using the linker GC-friendly
metadata scheme, everything would have worked, but clang does not enable
it by default.

llvm-svn: 340232
2018-08-20 23:35:45 +00:00
Vedant Kumar ee6c233ae0 [InstrProf] Use atomic profile counter updates for TSan
Thread sanitizer instrumentation fails to skip all loads and stores to
profile counters. This can happen if profile counter updates are merged:

  %.sink = phi i64* ...
  %pgocount5 = load i64, i64* %.sink
  %27 = add i64 %pgocount5, 1
  %28 = bitcast i64* %.sink to i8*
  call void @__tsan_write8(i8* %28)
  store i64 %27, i64* %.sink

To suppress TSan diagnostics about racy counter updates, make the
counter updates atomic when TSan is enabled. If there's general interest
in this mode it can be surfaced as a clang/swift driver option.

Testing: check-{llvm,clang,profile}

rdar://40477803

Differential Revision: https://reviews.llvm.org/D50867

llvm-svn: 339955
2018-08-16 22:24:47 +00:00
Easwaran Raman aca738b742 [BFI] Use rounding while computing profile counts.
Summary:
Profile count of a block is computed by multiplying its block frequency
by entry count and dividing the result by entry block frequency. Do
rounded division in the last step and update test cases appropriately.

Reviewers: davidxl

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D50822

llvm-svn: 339835
2018-08-16 00:26:59 +00:00
Evgeniy Stepanov 453e7ac785 [hwasan] Add -hwasan-with-ifunc flag.
Summary: Similar to asan's flag, it can be used to disable the use of ifunc to access hwasan shadow address.

Reviewers: vitalybuka, kcc

Subscribers: srhines, hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D50544

llvm-svn: 339447
2018-08-10 16:21:37 +00:00
Alexander Potapenko 75a954330b [MSan] Shrink the register save area for non-SSE builds
If code is compiled for X86 without SSE support, the register save area
doesn't contain FPU registers, so `AMD64FpEndOffset` should be equal to
`AMD64GpEndOffset`.

llvm-svn: 339414
2018-08-10 08:06:43 +00:00
Joel Galenson cfe5bc158d Fix crash in bounds checking.
In r337830 I added SCEV checks to enable us to insert fewer bounds checks.  Unfortunately, this sometimes crashes when multiple bounds checks are added due to SCEV caching issues.  This patch splits the bounds checking pass into two phases, one that computes all the conditions (using SCEV checks) and the other that adds the new instructions.

Differential Revision: https://reviews.llvm.org/D49946

llvm-svn: 338902
2018-08-03 17:12:23 +00:00
John Baldwin c5d7e04052 [ASAN] Use the correct shadow offset for ASAN on FreeBSD/mips64.
Reviewed By: atanasyan

Differential Revision: https://reviews.llvm.org/D49939

llvm-svn: 338650
2018-08-01 22:51:13 +00:00
Reid Kleckner ba82788ff6 [InstrProf] Don't register __llvm_profile_runtime_user
Refactor some FileCheck prefixes while I'm at it.

Fixes PR38340

llvm-svn: 338172
2018-07-27 22:21:35 +00:00
Reid Kleckner c6cf918f44 [InstrProf] Use comdats on COFF for available_externally functions
Summary:
r262157 added ELF-specific logic to put a comdat on the __profc_*
globals created for available_externally functions. We should be able to
generalize that logic to all object file formats that support comdats,
i.e. everything other than MachO. This fixes duplicate symbol errors,
since on COFF, linkonce_odr doesn't make the symbol weak.

Fixes PR38251.

Reviewers: davidxl, xur

Subscribers: hiraditya, dmajor, llvm-commits, aheejin

Differential Revision: https://reviews.llvm.org/D49882

llvm-svn: 338082
2018-07-26 22:59:17 +00:00
Joel Galenson 8dbcc58917 Use SCEV to avoid inserting some bounds checks.
This patch uses SCEV to avoid inserting some bounds checks when they are not needed.  This slightly improves the performance of code compiled with the bounds check sanitizer.

Differential Revision: https://reviews.llvm.org/D49602

llvm-svn: 337830
2018-07-24 15:21:54 +00:00
Alexander Potapenko 5ff3abbc31 [MSan] run materializeChecks() before materializeStores()
When pointer checking is enabled, it's important that every pointer is
checked before its value is used.
For stores MSan used to generate code that calculates shadow/origin
addresses from a pointer before checking it.
For userspace this isn't a problem, because the shadow calculation code
is quite simple and compiler is able to move it after the check on -O2.
But for KMSAN getShadowOriginPtr() creates a runtime call, so we want the
check to be performed strictly before that call.

Swapping materializeChecks() and materializeStores() resolves the issue:
both functions insert code before the given IR location, so the new
insertion order guarantees that the code calculating shadow address is
between the address check and the memory access.

llvm-svn: 337571
2018-07-20 16:28:49 +00:00
Peter Collingbourne 4a653fa7f1 Rename __asan_gen_* symbols to ___asan_gen_*.
This prevents gold from printing a warning when trying to export
these symbols via the asan dynamic list after ThinLTO promotes them
from private symbols to external symbols with hidden visibility.

Differential Revision: https://reviews.llvm.org/D49498

llvm-svn: 337428
2018-07-18 22:23:14 +00:00
Michael J. Spencer 7bb2767fba Recommit r335794 "Add support for generating a call graph profile from Branch Frequency Info." with fix for removed functions.
llvm-svn: 337140
2018-07-16 00:28:24 +00:00
Joel E. Denny 9fa9c9368d [FileCheck] Add -allow-deprecated-dag-overlap to failing llvm tests
See https://reviews.llvm.org/D47106 for details.

Reviewed By: probinson

Differential Revision: https://reviews.llvm.org/D47171

This commit drops that patch's changes to:

  llvm/test/CodeGen/NVPTX/f16x2-instructions.ll
  llvm/test/CodeGen/NVPTX/param-load-store.ll

For some reason, the dos line endings there prevent me from commiting
via the monorepo.  A follow-up commit (not via the monorepo) will
finish the patch.

llvm-svn: 336843
2018-07-11 20:25:49 +00:00
Alex Shlyapnikov 788764ca12 [HWASan] Do not retag allocas before return from the function.
Summary:
Retagging allocas before returning from the function might help
detecting use after return bugs, but it does not work at all in real
life, when instrumented and non-instrumented code is intermixed.
Consider the following code:

F_non_instrumented() {
  T x;
  F1_instrumented(&x);
  ...
}

{
  F_instrumented();
  F_non_instrumented();
}

- F_instrumented call leaves the stack below the current sp tagged
  randomly for UAR detection
- F_non_instrumented allocates its own vars on that tagged stack,
  not generating any tags, that is the address of x has tag 0, but the
  shadow memory still contains tags left behind by F_instrumented on the
  previous step
- F1_instrumented verifies &x before using it and traps on tag mismatch,
  0 vs whatever tag was set by F_instrumented

Reviewers: eugenis

Subscribers: srhines, llvm-commits

Differential Revision: https://reviews.llvm.org/D48664

llvm-svn: 336011
2018-06-29 20:20:17 +00:00
Benjamin Kramer 269eb21e1c Revert "Add support for generating a call graph profile from Branch Frequency Info."
This reverts commits r335794 and r335797. Breaks ThinLTO+FDO selfhost.

llvm-svn: 335851
2018-06-28 13:15:03 +00:00
Michael J. Spencer 5bf1ead377 Add support for generating a call graph profile from Branch Frequency Info.
=== Generating the CG Profile ===

The CGProfile module pass simply gets the block profile count for each BB and scans for call instructions.  For each call instruction it adds an edge from the current function to the called function with the current BB block profile count as the weight.

After scanning all the functions, it generates an appending module flag containing the data. The format looks like:
```
!llvm.module.flags = !{!0}

!0 = !{i32 5, !"CG Profile", !1}
!1 = !{!2, !3, !4} ; List of edges
!2 = !{void ()* @a, void ()* @b, i64 32} ; Edge from a to b with a weight of 32
!3 = !{void (i1)* @freq, void ()* @a, i64 11}
!4 = !{void (i1)* @freq, void ()* @b, i64 20}
```

Differential Revision: https://reviews.llvm.org/D48105

llvm-svn: 335794
2018-06-27 23:58:08 +00:00
Evgeniy Stepanov 289a7d4c7d Revert "[asan] Instrument comdat globals on COFF targets"
Causes false positive ODR violation reports on __llvm_profile_raw_version.

llvm-svn: 335681
2018-06-26 22:43:48 +00:00
Chandler Carruth aa5f4d2e23 Revert r335306 (and r335314) - the Call Graph Profile pass.
This is the first pass in the main pipeline to use the legacy PM's
ability to run function analyses "on demand". Unfortunately, it turns
out there are bugs in that somewhat-hacky approach. At the very least,
it leaks memory and doesn't support -debug-pass=Structure. Unclear if
there are larger issues or not, but this should get the sanitizer bots
back to green by fixing the memory leaks.

llvm-svn: 335320
2018-06-22 05:33:57 +00:00
Michael J. Spencer fc93dd8e18 [Instrumentation] Add Call Graph Profile pass
This patch adds support for generating a call graph profile from Branch Frequency Info.

The CGProfile module pass simply gets the block profile count for each BB and scans for call instructions. For each call instruction it adds an edge from the current function to the called function with the current BB block profile count as the weight.

After scanning all the functions, it generates an appending module flag containing the data. The format looks like:

!llvm.module.flags = !{!0}

!0 = !{i32 5, !"CG Profile", !1}
!1 = !{!2, !3, !4} ; List of edges
!2 = !{void ()* @a, void ()* @b, i64 32} ; Edge from a to b with a weight of 32
!3 = !{void (i1)* @freq, void ()* @a, i64 11}
!4 = !{void (i1)* @freq, void ()* @b, i64 20}

Differential Revision: https://reviews.llvm.org/D48105

llvm-svn: 335306
2018-06-21 23:31:10 +00:00
Reid Kleckner 12395b7795 [WinASan] Don't instrument globals in sections containing '$'
Such globals are very likely to be part of a sorted section array, such
the .CRT sections used for dynamic initialization. The uses its own
sorted sections called ATL$__a, ATL$__m, and ATL$__z. Instead of special
casing them, just look for the dollar sign, which is what invokes linker
section sorting for COFF.

Avoids issues with ASan and the ATL uncovered after we started
instrumenting comdat globals on COFF.

llvm-svn: 334653
2018-06-13 20:47:21 +00:00
Reid Kleckner 0bab222084 [asan] Instrument comdat globals on COFF targets
Summary:
If we can use comdats, then we can make it so that the global metadata
is thrown away if the prevailing definition of the global was
uninstrumented. I have only tested this on COFF targets, but in theory,
there is no reason that we cannot also do this for ELF.

This will allow us to re-enable string merging with ASan on Windows,
reducing the binary size cost of ASan on Windows.

Reviewers: eugenis, vitalybuka

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D47841

llvm-svn: 334313
2018-06-08 18:33:16 +00:00
Evgeniy Stepanov 28f330fd6f [msan] Don't check divisor shadow in fdiv.
Summary:
Floating point division by zero or even undef does not have undefined
behavior and may occur due to optimizations.

Fixes https://bugs.llvm.org/show_bug.cgi?id=37523.

Reviewers: kcc

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D47085

llvm-svn: 332761
2018-05-18 20:19:53 +00:00
Walter Lee cdbb207bd1 [asan] Add instrumentation support for Myriad
1. Define Myriad-specific ASan constants.

2. Add code to generate an outer loop that checks that the address is
   in DRAM range, and strip the cache bit from the address.  The
   former is required because Myriad has no memory protection, and it
   is up to the instrumentation to range-check before using it to
   index into the shadow memory.

3. Do not add an unreachable instruction after the error reporting
   function; on Myriad such function may return if the run-time has
   not been initialized.

4. Add a test.

Differential Revision: https://reviews.llvm.org/D46451

llvm-svn: 332692
2018-05-18 04:10:38 +00:00
Evgeniy Stepanov 091fed94ae [msan] Instrument masked.store, masked.load intrinsics.
Summary: Instrument masked store/load intrinsics.

Reviewers: kcc

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D46785

llvm-svn: 332402
2018-05-15 21:28:25 +00:00
Craig Topper 38ad7ddabc [X86] Remove and autoupgrade cvtsi2ss/cvtsi2sd intrinsics to match what clang has used for a very long time.
llvm-svn: 332186
2018-05-12 23:14:39 +00:00
Kostya Serebryany a2759327fd [sanitizer-coverage] don't instrument a function if it's entry block ends with 'unreachable'
llvm-svn: 332072
2018-05-11 01:09:39 +00:00
Shiva Chen 2c864551df [DebugInfo] Add DILabel metadata and intrinsic llvm.dbg.label.
In order to set breakpoints on labels and list source code around
labels, we need collect debug information for labels, i.e., label
name, the function label belong, line number in the file, and the
address label located. In order to keep these information in LLVM
IR and to allow backend to generate debug information correctly.
We create a new kind of metadata for labels, DILabel. The format
of DILabel is

!DILabel(scope: !1, name: "foo", file: !2, line: 3)

We hope to keep debug information as much as possible even the
code is optimized. So, we create a new kind of intrinsic for label
metadata to avoid the metadata is eliminated with basic block.
The intrinsic will keep existing if we keep it from optimized out.
The format of the intrinsic is

llvm.dbg.label(metadata !1)

It has only one argument, that is the DILabel metadata. The
intrinsic will follow the label immediately. Backend could get the
label metadata through the intrinsic's parameter.

We also create DIBuilder API for labels to be used by Frontend.
Frontend could use createLabel() to allocate DILabel objects, and use
insertLabel() to insert llvm.dbg.label intrinsic in LLVM IR.

Differential Revision: https://reviews.llvm.org/D45024

Patch by Hsiangkai Wang.

llvm-svn: 331841
2018-05-09 02:40:45 +00:00
Chandler Carruth 16429acacb [x86] Revert r330322 (& r330323): Lowering x86 adds/addus/subs/subus intrinsics
The LLVM commit introduces a crash in LLVM's instruction selection.

I filed http://llvm.org/PR37260 with the test case.

llvm-svn: 330997
2018-04-26 21:46:01 +00:00
Alex Shlyapnikov 99cf54baa6 [HWASan] Introduce non-zero based and dynamic shadow memory (LLVM).
Summary:
Support the dynamic shadow memory offset (the default case for user
space now) and static non-zero shadow memory offset
(-hwasan-mapping-offset option). Keeping the the latter case around
for functionality and performance comparison tests (and mostly for
-hwasan-mapping-offset=0 case).

The implementation is stripped down ASan one, picking only the relevant
parts in the following assumptions: shadow scale is fixed, the shadow
memory is dynamic, it is accessed via ifunc global, shadow memory address
rematerialization is suppressed.

Keep zero-based shadow memory for kernel (-hwasan-kernel option) and
calls instreumented case (-hwasan-instrument-with-calls option), which
essentially means that the generated code is not changed in these cases.

Reviewers: eugenis

Subscribers: srhines, llvm-commits

Differential Revision: https://reviews.llvm.org/D45840

llvm-svn: 330475
2018-04-20 20:04:04 +00:00
Alexander Ivchenko e8fed1546e Lowering x86 adds/addus/subs/subus intrinsics (llvm part)
This is the patch that lowers x86 intrinsics to native IR
in order to enable optimizations. The patch also includes folding
of previously missing saturation patterns so that IR emits the same
machine instructions as the intrinsics.

Patch by tkrupa

Differential Revision: https://reviews.llvm.org/D44785

llvm-svn: 330322
2018-04-19 12:13:30 +00:00
Andrey Konovalov 1ba9d9c6ca hwasan: add -fsanitize=kernel-hwaddress flag
This patch adds -fsanitize=kernel-hwaddress flag, that essentially enables
-hwasan-kernel=1 -hwasan-recover=1 -hwasan-match-all-tag=0xff.

Differential Revision: https://reviews.llvm.org/D45046

llvm-svn: 330044
2018-04-13 18:05:21 +00:00
Evgeniy Stepanov 1f1a7a719d hwasan: add -hwasan-match-all-tag flag
Sometimes instead of storing addresses as is, the kernel stores the address of
a page and an offset within that page, and then computes the actual address
when it needs to make an access. Because of this the pointer tag gets lost
(gets set to 0xff). The solution is to ignore all accesses tagged with 0xff.

This patch adds a -hwasan-match-all-tag flag to hwasan, which allows to ignore
accesses through pointers with a particular pointer tag value for validity.

Patch by Andrey Konovalov.

Differential Revision: https://reviews.llvm.org/D44827

llvm-svn: 329228
2018-04-04 20:44:59 +00:00
Alexander Potapenko ac70668cff MSan: introduce the conservative assembly handling mode.
The default assembly handling mode may introduce false positives in the
cases when MSan doesn't understand that the assembly call initializes
the memory pointed to by one of its arguments.

We introduce the conservative mode, which initializes the first
|sizeof(type)| bytes for every |type*| pointer passed into the
assembly statement.

llvm-svn: 329054
2018-04-03 09:50:06 +00:00
Peter Collingbourne d03bf12c1b DataFlowSanitizer: wrappers of functions with local linkage should have the same linkage as the function being wrapped
This patch resolves link errors when the address of a static function is taken, and that function is uninstrumented by DFSan.

This change resolves bug 36314.

Patch by Sam Kerner!

Differential Revision: https://reviews.llvm.org/D44784

llvm-svn: 328890
2018-03-30 18:37:55 +00:00
Evgeniy Stepanov 50635dab26 Add msan custom mapping options.
Similarly to https://reviews.llvm.org/D18865 this adds options to provide custom mapping for msan.
As discussed in http://lists.llvm.org/pipermail/llvm-dev/2018-February/121339.html

Patch by vit9696(at)avp.su.

Differential Revision: https://reviews.llvm.org/D44926

llvm-svn: 328830
2018-03-29 21:18:17 +00:00
Alex Shlyapnikov 83e7841419 [HWASan] Port HWASan to Linux x86-64 (LLVM)
Summary:
Porting HWASan to Linux x86-64, first of the three patches, LLVM part.

The approach is similar to ARM case, trap signal is used to communicate
memory tag check failure. int3 instruction is used to generate a signal,
access parameters are stored in nop [eax + offset] instruction immediately
following the int3 one.

One notable difference is that x86-64 has to untag the pointer before use
due to the lack of feature comparable to ARM's TBI (Top Byte Ignore).

Reviewers: eugenis

Subscribers: kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D44699

llvm-svn: 328342
2018-03-23 17:57:54 +00:00
Kuba Mracek 8842da8e07 [asan] Fix a false positive ODR violation due to LTO ConstantMerge pass [llvm part, take 3]
This fixes a false positive ODR violation that is reported by ASan when using LTO. In cases, where two constant globals have the same value, LTO will merge them, which breaks ASan's ODR detection.

Differential Revision: https://reviews.llvm.org/D43959

llvm-svn: 327061
2018-03-08 21:02:18 +00:00
Kuba Mracek f0bcbfef5c Revert r327053.
llvm-svn: 327055
2018-03-08 20:13:39 +00:00
Kuba Mracek 584bd10803 [asan] Fix a false positive ODR violation due to LTO ConstantMerge pass [llvm part, take 2]
This fixes a false positive ODR violation that is reported by ASan when using LTO. In cases, where two constant globals have the same value, LTO will merge them, which breaks ASan's ODR detection.

Differential Revision: https://reviews.llvm.org/D43959

llvm-svn: 327053
2018-03-08 20:05:45 +00:00
David Zarzycki c71c9aace8 [Tests] Remove empty test file that causes the test suite to fail
This empty file was "created" by r327033, which attempted to revert
r327029, which introduced the file.

llvm-svn: 327036
2018-03-08 18:03:15 +00:00
Kuba Mracek e834b22874 Revert r327029
llvm-svn: 327033
2018-03-08 17:32:00 +00:00
Kuba Mracek 0e06d37dba [asan] Fix a false positive ODR violation due to LTO ConstantMerge pass [llvm part]
This fixes a false positive ODR violation that is reported by ASan when using LTO. In cases, where two constant globals have the same value, LTO will merge them, which breaks ASan's ODR detection.

Differential Revision: https://reviews.llvm.org/D43959

llvm-svn: 327029
2018-03-08 17:24:06 +00:00
Vedant Kumar 9a041a7522 [InstrProfiling] Emit the runtime hook when no counters are lowered
The API verification tool tapi has difficulty processing frameworks
which enable code coverage, but which have no code. The profile lowering
pass does not emit the runtime hook in this case because no counters are
lowered.

While the hook is not needed for program correctness (the profile
runtime doesn't have to be linked in), it's needed to allow tapi to
validate the exported symbol set of instrumented binaries.

It was not possible to add a workaround in tapi for empty binaries due
to an architectural issue: tapi generates its expected symbol set before
it inspects a binary. Changing that model has a higher cost than simply
forcing llvm to always emit the runtime hook.

rdar://36076904

Differential Revision: https://reviews.llvm.org/D43794

llvm-svn: 326350
2018-02-28 19:00:08 +00:00