https://luci-logdog.appspot.com/v/?s=chromium%2Fbb%2Fchromium.fyi%2FClangToTLinuxUBSanVptr%2F6310%2F%2B%2Frecipes%2Fsteps%2Fcompile%2F0%2Fstdout

[1/51901] CXX obj/base/base_static/base_switches.o
FAILED: obj/base/base_static/base_switches.o 
../../third_party/llvm-build/Release+Asserts/bin/clang++ -MMD -MF obj/base/base_static/base_switches.o.d -DV8_DEPRECATION_WARNINGS -DUSE_UDEV -DUSE_AURA=1 -DUSE_PANGO=1 -DUSE_CAIRO=1 -DUSE_GLIB=1 -DUSE_NSS_CERTS=1 -DUSE_X11=1 -DUNDEFINED_SANITIZER -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL -DCHROMIUM_BUILD -DFIELDTRIAL_TESTING_ENABLED -DCR_CLANG_REVISION=\"309566\" -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -DSANITIZER_COVERAGE -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -I../.. -Igen -fno-strict-aliasing --param=ssp-buffer-size=4 -fstack-protector -Wno-builtin-macro-redefined -D__DATE__= -D__TIME__= -D__TIMESTAMP__= -funwind-tables -fPIC -pipe -B../../third_party/binutils/Linux_x64/Release/bin -pthread -fcolor-diagnostics -m64 -march=x86-64 -Wall -Werror -Wextra -Wno-missing-field-initializers -Wno-unused-parameter -Wno-c++11-narrowing -Wno-covered-switch-default -Wno-unneeded-internal-declaration -Wno-inconsistent-missing-override -Wno-undefined-var-template -Wno-nonportable-include-path -Wno-address-of-packed-member -Wno-unused-lambda-capture -Wno-user-defined-warnings -fno-omit-frame-pointer -g1 --sysroot=../../build/linux/debian_jessie_amd64-sysroot -gline-tables-only -gcolumn-info -fno-omit-frame-pointer -fsanitize-coverage=trace-pc-guard -mllvm -sanitizer-coverage-prune-blocks=1 -fno-sanitize-recover=undefined -fsanitize=vptr -fsanitize-blacklist=../../tools/ubsan/vptr_blacklist.txt -fvisibility=hidden -Wheader-hygiene -Wstring-conversion -Wtautological-overlap-compare -O2 -fno-ident -fdata-sections -ffunction-sections -std=gnu++14 -nostdinc++ -isystem../../buildtools/third_party/libc++/trunk/include -isystem../../buildtools/third_party/libc++abi/trunk/include -fno-exceptions -fvisibility-inlines-hidden -c ../../base/base_switches.cc -o obj/base/base_static/base_switches.o
clang-6.0: error: implicitly disabling vptr sanitizer because null checking wasn't enabled [-Werror,-Wauto-disable-vptr-sanitizer]



http://llvm.org/viewvc/llvm-project?view=revision&revision=309007

I'm not sure what this warning is supposed to mean; I'll ask upstream.