Fix stack_trace_compressor builds for Clang < 6.0

[hctim]

Summary

Clang 4.* doesn't supply -fsanitize=fuzzer, and Clang 5.* doesn't supply
-fsanitize=fuzzer-no-link. Generally, in LLVM, fuzz targets are added through
the add_llvm_fuzzer build rule, which can't be used in compiler-rt (as it has
to be able to be standalone built).

Instead of adding tooling to add a dummy main (which kind of defeats the
purpose of these fuzz targets), we instead build the fuzz target only when the
Clang version is >= 6.*.

[tejohnson]

LGTM. Fixes my build issue!

[sylvestre.ledru]

@hctim

On Ubuntu Xenial with cmake 3.5.1, it fails with:

Make Error at projects/compiler-rt/lib/gwp_asan/CMakeLists.txt:108 (if):
  if given arguments:

    "COMPILER_RT_BUILD_LIBFUZZER" "AND" "GNU" "STREQUAL" "Clang" "AND" "CMAKE_CXX_COMPILER_VERSION" "VERSION_GREATER_EQUAL" "6.0"

  Unknown arguments specified

Any idea how to fix this? Thanks

[tejohnson]

In D66682#1644286, @sylvestre.ledru wrote:

@hctim

On Ubuntu Xenial with cmake 3.5.1, it fails with:

Make Error at projects/compiler-rt/lib/gwp_asan/CMakeLists.txt:108 (if):
  if given arguments:

    "COMPILER_RT_BUILD_LIBFUZZER" "AND" "GNU" "STREQUAL" "Clang" "AND" "CMAKE_CXX_COMPILER_VERSION" "VERSION_GREATER_EQUAL" "6.0"

  Unknown arguments specified

Any idea how to fix this? Thanks

Looks like cmake evaluates the VERSION_GREATER_EQUAL before the AND (https://cmake.org/cmake/help/v3.5/command/if.html#condition-syntax), which presumably leads to this issue since GNU must not have CMAKE_CXX_COMPILER_VERSION defined. According to that cmake documentation, parentheses could be added to force the correct evaluation order. Can you check if the following fixes your issue:

if (COMPILER_RT_BUILD_LIBFUZZER AND
    ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang") AND
    CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 6.0)

If that still fails then I guess it will be necessary to use nested ifs.

[sylvestre.ledru]

@tejohnson Nested if ? :)

CMake Error at projects/compiler-rt/lib/gwp_asan/CMakeLists.txt:108 (if):
  if given arguments:

    "COMPILER_RT_BUILD_LIBFUZZER" "AND" "(" "GNU" "STREQUAL" "Clang" ")" "AND" "CMAKE_CXX_COMPILER_VERSION" "VERSION_GREATER_EQUAL" "6.0"

  Unknown arguments specified

[dyung]

In D66682#1644676, @sylvestre.ledru wrote:

@tejohnson Nested if ? :)

CMake Error at projects/compiler-rt/lib/gwp_asan/CMakeLists.txt:108 (if):
  if given arguments:

    "COMPILER_RT_BUILD_LIBFUZZER" "AND" "(" "GNU" "STREQUAL" "Clang" ")" "AND" "CMAKE_CXX_COMPILER_VERSION" "VERSION_GREATER_EQUAL" "6.0"

  Unknown arguments specified

We are seeing the same failure in our internal upstream builder using CMake 3.4.3.

Looking at the CMake documentation, the problem might be the use of VERSION_GREATER_EQUAL.. It appears that binary test operator was not added to CMake until 3.7.

So the best fix would probably be to use two comparisons, maybe something like this:

((CMAKE_CXX_COMPILER_VERSION VERSION_EQUAL 6.0) OR (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 6.0))

[bjope]

FYI: I made a fixup here https://reviews.llvm.org/rL369891

I see here that you suspect other problems (around usage of AND). The problem I solved was related to older cmake versions not supporting VERSION_GREATER_EQUAL.

[tejohnson]

In D66682#1644676, @sylvestre.ledru wrote:

@tejohnson Nested if ? :)

I meant something like:
if (...)

if (...)

but in any case this wasn't the problem at all.

In D66682#1644869, @bjope wrote:

FYI: I made a fixup here https://reviews.llvm.org/rL369891

I see here that you suspect other problems (around usage of AND). The problem I solved was related to older cmake versions not supporting VERSION_GREATER_EQUAL.

Got it thanks.

[sylvestre.ledru]

In D66682#1645092, @tejohnson wrote:

In D66682#1644676, @sylvestre.ledru wrote:

@tejohnson Nested if ? :)

I meant something like:
if (...)

if (...)

Sure, I meant that we could try with this solution :)

compiler-rt/trunk/lib/gwp_asan/CMakeLists.txt

add_compiler_rt_object_libraries(RTGwpAsanBacktraceLibc
       ADDITIONAL_HEADERS ${GWP_ASAN_BACKTRACE_HEADERS}
       CFLAGS ${GWP_ASAN_CFLAGS})
   add_compiler_rt_object_libraries(RTGwpAsanBacktraceSanitizerCommon
       ARCHS ${GWP_ASAN_SUPPORTED_ARCH}
       SOURCES optional/backtrace_sanitizer_common.cpp
       ADDITIONAL_HEADERS ${GWP_ASAN_BACKTRACE_HEADERS}
       CFLAGS ${GWP_ASAN_CFLAGS} ${SANITIZER_COMMON_CFLAGS})
 
-  # Build the stack trace compressor fuzzer.
-  if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang" AND
-      COMPILER_RT_BUILD_LIBFUZZER)
+  # Build the stack trace compressor fuzzer. Note that clang versions 4.* did
+  # not have -fsanitize=fuzzer, and Clang versions 5.* didn't have
+  # -fsanitize=fuzzer-no-link. In general, the way we build fuzz targets in LLVM
+  # core is to link it against a dummy main when DLLVM_USE_SANITIZE_COVERAGE
+  # isn't specified. Instead, here we only build fuzz targets if clang version
+  # is >= 6.0.
+  if (COMPILER_RT_BUILD_LIBFUZZER AND
+      "${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang" AND
+      CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 6.0)
     add_executable(stack_trace_compressor_fuzzer
         stack_trace_compressor_fuzzer.cpp
         ${GWP_ASAN_SOURCES}
         ${GWP_ASAN_HEADERS})
     set_target_properties(
         stack_trace_compressor_fuzzer PROPERTIES FOLDER "Fuzzers")
     target_compile_options(
         stack_trace_compressor_fuzzer PRIVATE -fsanitize=fuzzer-no-link)