Build Linux apps against libwebrtc with custom libstdc++

[Aaron Clauson]

Hi,

I've spent some time experimenting with building libwebrtc on Linux. I have managed to find a happy path where my app can link to libwebrtc-full.a but only in the case where it is built with a gn arg of "use_custom_libcxx=false". I'd like to know how to build an app that can use the custom libstdc++, which is the default from the libwebrtc build instructions.

A summary of the steps for my attempts are at the end of this email. But in short my question boils down to how can I build the webrtc_lib_link_test app that is part of the webrtc source tree when libwebrtc is built with "gn gen out/Default", i.e. no args?

After attempting to copy the clang++ instructions from the main build I came up with the compile and link commands below which do work but the executable fails with a segmentation fault. I'm not at all familiar with using sysroot so could be doing something silly.

$ clang++ -D_LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS -D_LIBCPP_DEBUG=0 -D_DEBUG -DWEBRTC_POSIX -DWEBRTC_LINUX -I/src/webrtc-checkout/src -I/src/webrtc-checkout/src/third_party/abseil-cpp -fstack-protector -funwind-tables -fPIC -O0 -g2 -ggnu-pubnames -std=c++14 -fno-trigraphs -nostdinc++ -isystem/src/webrtc-checkout/src/buildtools/third_party/libc++/trunk/include --sysroot=/src/webrtc-checkout/src/build/linux/debian_sid_amd64-sysroot -c webrtc_lib_link_test.cc -o webrtc_lib_link_test.o

$ clang++ -fuse-ld=lld -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now  -Wl,-z,defs -Wl,--as-needed --sysroot=/src/webrtc-checkout/src/build/linux/debian_sid_amd64-sysroot -L/src/webrtc-checkout/src/build/linux/debian_sid_amd64-sysroot/lib/x86_64-linux-gnu -L/src/webrtc-checkout/src/build/linux/debian_sid_amd64-sysroot/usr/lib/x86_64-linux-gnu -L/src/webrtc-checkout/src/out/Default -pie -o webrtc_lib_link_test webrtc_lib_link_test.o -lwebrtc-full -ldl -lpthread -lX11 -lglib-2.0

$ ./webrtc_lib_link_test
(audio_device_impl.cc:84): CreateForTest
    Segmentation fault (core dumped)

Thanks,

Aaron

Detailed steps for build experiments:

## Common set up steps:

sudo apt update && DEBIAN_FRONTEND="noninteractive" apt install -y curl git \
  lsb-release python sudo wget
 
# Get depot_tools
mkdir /src && chown $USER:$USER /src && cd /src
git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git --depth 1 depot_tools
export PATH="/src/depot_tools:${PATH}"

# Get libwebrtc source.
mkdir /src/webrtc-checkout && cd /src/webrtc-checkout
fetch --nohooks webrtc
cd /src/webrtc-checkout/src
git pull origin master
gclient sync
build/install-build-deps.sh

## Run build tests on Ubuntu Xenial 16.04:

 # xenial.1: Test default build steps
   $ gn gen out/Default
   $ ninja all -C out/Default
   $ out/Default/webrtc_lib_link_test
   
   result: OK
   
  # xenial.2: Test default steps followed by re-build webrtc_lib_link_test
    $ gn gen out/Default
    $ ninja all -C out/Default
    $ out/Default/webrtc_lib_link_test
$ ar crs out/Default/libwebrtc-full.a $(find out/Default/obj -name '*\.o')
$ export PATH="/src/webrtc-checkout/src/third_party/llvm-build/Release+Asserts/bin":${PATH}
    $ clang++ -D_LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS -D_LIBCPP_DEBUG=0 -D_DEBUG -DWEBRTC_POSIX -DWEBRTC_LINUX -I/src/webrtc-checkout/src -I/src/webrtc-checkout/src/third_party/abseil-cpp -fstack-protector -funwind-tables -fPIC -O0 -g2 -ggnu-pubnames -std=c++14 -fno-trigraphs -nostdinc++ -isystem/src/webrtc-checkout/src/buildtools/third_party/libc++/trunk/include --sysroot=/src/webrtc-checkout/src/build/linux/debian_sid_amd64-sysroot -c webrtc_lib_link_test.cc -o webrtc_lib_link_test.o
$ clang++ -fuse-ld=lld -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now  -Wl,-z,defs -Wl,--as-needed --sysroot=/src/webrtc-checkout/src/build/linux/debian_sid_amd64-sysroot -L/src/webrtc-checkout/src/build/linux/debian_sid_amd64-sysroot/lib/x86_64-linux-gnu -L/src/webrtc-checkout/src/build/linux/debian_sid_amd64-sysroot/usr/lib/x86_64-linux-gnu -L/src/webrtc-checkout/src/out/Default -pie -o webrtc_lib_link_test webrtc_lib_link_test.o -lwebrtc-full -ldl -lpthread -lX11 -lglib-2.0
$ ./webrtc_lib_link_test

result: Segmentation fault
$ ./webrtc_lib_link_test
(audio_device_impl.cc:84): CreateForTest
    Segmentation fault (core dumped)

  # xenial.3: Test no custom libcxx build
    $ gn gen out/Default --args="is_component_build=false use_custom_libcxx=false use_custom_libcxx_for_host=false rtc_enable_protobuf=false"
$ ninja all -C out/Default

result: build fails, compilation error.

  # xenial.4: Test no custom libcxx build with patch
    $ git apply patch-nocustomlibcxx.diff
$ pushd base; git apply ../patch-base-nocustomlibcxx.diff; popd
$ gn gen out/Default --args="is_component_build=false use_custom_libcxx=false use_custom_libcxx_for_host=false rtc_enable_protobuf=false"
$ ninja all -C out/Default
$ out/Default/webrtc_lib_link_test

result: webrtc_lib_link_test execution fails: out/Default/webrtc_lib_link_test: /usr/lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.22' not found (required by out/Default/webrtc_lib_link_test)

  # xenial.5: Test no custom libcxx build with patch and libstdc++ update
    $ git apply patch-nocustomlibcxx.diff
$ pushd base; git apply ../patch-base-nocustomlibcxx.diff; popd
$ gn gen out/Default --args="is_component_build=false use_custom_libcxx=false use_custom_libcxx_for_host=false rtc_enable_protobuf=false"
$ ninja all -C out/Default
$ sudo apt install software-properties-common
    $ sudo add-apt-repository ppa:ubuntu-toolchain-r/test
    $ sudo apt update
    $ sudo apt install libstdc++-9-dev
$ out/Default/webrtc_lib_link_test

result: OK

  # xenial.6: Test no custom libcxx build with patch and libstdc++ update followed by re-build webrtc_lib_link_test
    $ git apply patch-nocustomlibcxx.diff
$ pushd base; git apply ../patch-base-nocustomlibcxx.diff; popd
$ gn gen out/Default --args="is_component_build=false use_custom_libcxx=false use_custom_libcxx_for_host=false rtc_enable_protobuf=false"
$ ninja all -C out/Default
$ sudo apt install software-properties-common
    $ sudo add-apt-repository ppa:ubuntu-toolchain-r/test
    $ sudo apt update
    $ sudo apt install libstdc++-9-dev
$ out/Default/webrtc_lib_link_test
$ ar crs out/Default/libwebrtc-full.a $(find out/Default/obj -name '*\.o')
$ export PATH="/src/webrtc-checkout/src/third_party/llvm-build/Release+Asserts/bin":${PATH}
$ clang++ -D_LIBCPP_ABI_UNSTABLE -D_LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS -D_DEBUG -DWEBRTC_POSIX -DWEBRTC_LINUX -I/src/webrtc-checkout/src -I/src/webrtc-checkout/src/third_party/abseil-cpp -fstack-protector -funwind-tables -fPIC -O0 -g2 -std=c++14 -c webrtc_lib_link_test.cc -o webrtc_lib_link_test.o
$ clang++ -fuse-ld=lld -Wl,-z,noexecstack -Wl,-z,relro -L/src/webrtc-checkout/src/out/Default -pie -o webrtc_lib_link_test webrtc_lib_link_test.o -lwebrtc-full -ldl -lpthread -lX11 -lglib-2.0 -lstdc++ -latomic
$ ./webrtc_lib_link_test

result: OK

  # xenial.7:  Test no custom libcxx build with patch and libstdc++ update followed by re-build webrtc_lib_link_test including libevent dependency
    $ git apply patch-nocustomlibcxx.diff
$ pushd base; git apply ../patch-base-nocustomlibcxx.diff; popd
$ gn gen out/Default --args="is_component_build=false use_custom_libcxx=false use_custom_libcxx_for_host=false rtc_enable_protobuf=false"
$ ninja all -C out/Default
$ sudo apt install software-properties-common
    $ sudo add-apt-repository ppa:ubuntu-toolchain-r/test
    $ sudo apt update
    $ sudo apt install libstdc++-9-dev
$ out/Default/webrtc_lib_link_test
$ ar crs out/Default/libwebrtc-full.a $(find out/Default/obj -name '*\.o')
$ export PATH="/src/webrtc-checkout/src/third_party/llvm-build/Release+Asserts/bin":${PATH}
$ apt install libevent-dev
    $ clang++ -D_LIBCPP_ABI_UNSTABLE -D_LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS -D_DEBUG -DWEBRTC_POSIX -DWEBRTC_LINUX -I/src/webrtc-checkout/src -I/src/webrtc-checkout/src/third_party/abseil-cpp -fstack-protector -funwind-tables -fPIC -O0 -g2 -std=c++14 -c webrtc_lib_link_test_libevent.cc -o webrtc_lib_link_test_libevent.o
$ clang++ -fuse-ld=lld -Wl,-z,noexecstack -Wl,-z,relro -L/src/webrtc-checkout/src/out/Default -pie -o webrtc_lib_link_test_libevent webrtc_lib_link_test_libevent.o -lwebrtc-full -levent -ldl -lpthread -lX11 -lglib-2.0 -lstdc++ -latomic
$ ./webrtc_lib_link_test

result: OK
 (audio_device_impl.cc:319): ~AudioDeviceModuleImpl
      (audio_device_buffer.cc:75): AudioDeviceBuffer::~dtor
      libevnet version 1.4.13-stable.

# Note this patch adds single include of, #include <cstdint>, to modules/video_coding/decoding_state.h.
cat patch-nocustomlibcxx.diff
diff --git a/modules/video_coding/decoding_state.h b/modules/video_coding/decoding_state.h
index b87fb2d..ec97294 100644
--- a/modules/video_coding/decoding_state.h
+++ b/modules/video_coding/decoding_state.h
@@ -11,6 +11,7 @@
 #ifndef MODULES_VIDEO_CODING_DECODING_STATE_H_
 #define MODULES_VIDEO_CODING_DECODING_STATE_H_

+#include <cstdint>
 #include <map>
 #include <set>
 #include <vector>

# Note this patch adds single include of, #include <cstring>, to base/profiler/stack_copier_signal.cc.
cat patch-base-nocustomlibcxx.diff
diff --git a/profiler/stack_copier_signal.cc b/profiler/stack_copier_signal.cc
index cd3133d..047db3b 100644
--- a/profiler/stack_copier_signal.cc
+++ b/profiler/stack_copier_signal.cc
@@ -10,6 +10,7 @@
 #include <syscall.h>

 #include <atomic>
+#include <cstring>

 #include "base/notreached.h"
 #include "base/profiler/register_context.h"
 
Misc Notes:
 - Ubuntu Xenial 16.04 is mentioned as the main Chromium develoment platform https://chromium.googlesource.com/chromium/src/+/master/docs/linux/build_instructions.md.
 - PR submitted for patch to modules/video_coding/decoding_state.h https://webrtc-review.googlesource.com/c/src/+/211762