[VL][Ubuntu] Build fails linking libvelox.so: system libgflags.a not compiled with -fPIC

[dharanad]

Environment

• OS: Ubuntu 22.04 (also affects Ubuntu 20.04)
• Backend: Velox
• Build type: Dynamic (non-vcpkg)

Problem

Building Gluten with the Velox backend on Ubuntu fails at the libvelox.so link step with:

/usr/bin/ld: /usr/lib/x86_64-linux-gnu/libgflags.a(gflags.cc.o): relocation R_X86_64_PC32 against symbol 'stderr@@GLIBC_2.2.5' can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: final link failed: bad value
collect2: error: ld returned 1 exit status

Root Cause

scripts/setup-ubuntu.sh installs gflags via apt-get install libgflags-dev. The apt-packaged libgflags.a on Ubuntu is not compiled with -fPIC, so the linker rejects it when it is pulled into libvelox.so (a shared library).

The issue is in setup-ubuntu.sh:113:

libgflags-dev \   # <-- apt version is not PIC-compiled

Folly's installed cmake config (/usr/local/lib/cmake/folly/folly-targets.cmake) hardcodes gflags_static as a link dependency, which resolves to the non-PIC /usr/lib/x86_64-linux-gnu/libgflags.a.

Why Only Ubuntu

setup-centos8.sh and setup-openeuler24.sh both have a dedicated install_gflags function that:

1. Removes the system package (dnf remove -y gflags)
2. Builds gflags from source with cmake_install_dir gflags -DBUILD_SHARED_LIBS=ON -DBUILD_STATIC_LIBS=ON

setup-ubuntu.sh is missing this function entirely.

Fix

Add an install_gflags function to setup-ubuntu.sh, mirroring what setup-centos8.sh does:

function install_gflags {
  # Remove apt version (not PIC-compiled, cannot be linked into shared libs)
  sudo apt-get remove -y libgflags-dev
  wget_and_untar https://github.com/gflags/gflags/archive/v2.2.2.tar.gz gflags
  cmake_install_dir gflags \
    -DCMAKE_POSITION_INDEPENDENT_CODE=ON \
    -DBUILD_SHARED_LIBS=ON \
    -DBUILD_STATIC_LIBS=ON \
    -DBUILD_gflags_LIB=ON
}

And call it from install_dependencies before building Folly (since Folly's cmake export will then reference the PIC-compiled version).

Workaround

Until fixed, users on Ubuntu can manually build gflags with PIC before running the Gluten build:

sudo apt-get remove -y libgflags-dev
cd /tmp
wget https://github.com/gflags/gflags/archive/v2.2.2.tar.gz -O gflags.tar.gz
tar -xzf gflags.tar.gz && cd gflags-2.2.2
cmake -B build \
  -DCMAKE_POSITION_INDEPENDENT_CODE=ON \
  -DBUILD_SHARED_LIBS=ON \
  -DBUILD_STATIC_LIBS=ON \
  -DBUILD_gflags_LIB=ON \
  -DCMAKE_INSTALL_PREFIX=/usr/local \
  -DCMAKE_BUILD_TYPE=Release
sudo cmake --build build -j4 --target install
# Reinstall glog-dev (removed as a side effect)
sudo apt-get install -y libgoogle-glog-dev

Note

Removing libgflags-dev also removes libgoogle-glog-dev as a side effect (apt dependency), causing a secondary glog/logging.h: No such file or directory error. The workaround above includes reinstalling libgoogle-glog-dev.

[dharanad]

Suggested Fix

The change is in ep/build-velox/src/setup-ubuntu.sh (the Gluten-maintained wrapper around Velox's Ubuntu setup script). Two modifications are needed:

1. Remove libgflags-dev from the apt install list

In install_velox_deps_from_apt, remove libgflags-dev so the non-PIC apt package is never installed:

 function install_velox_deps_from_apt {
   ${SUDO} apt update
   ${SUDO} apt install -y \
     libc-ares-dev \
     libcurl4-openssl-dev \
     libssl-dev \
     libicu-dev \
     libdouble-conversion-dev \
     libgoogle-glog-dev \
     libbz2-dev \
-    libgflags-dev \
     libgtest-dev \
     libgmock-dev \

2. Add install_gflags function and call it before install_folly

Mirrors the pattern already used in setup-centos8.sh and setup-openeuler24.sh. Must be called before install_folly since Folly's cmake export bakes in the gflags library path at build time.

+function install_gflags {
+  # The apt-packaged libgflags.a is not compiled with -fPIC, which causes a
+  # linker error when it is pulled into libvelox.so (a shared library).
+  # Build from source with PIC enabled, matching what setup-centos8.sh does.
+  ${SUDO} apt-get remove -y libgflags-dev || true
+  wget_and_untar https://github.com/gflags/gflags/archive/v2.2.2.tar.gz gflags
+  cmake_install_dir gflags \
+    -DCMAKE_POSITION_INDEPENDENT_CODE=ON \
+    -DBUILD_SHARED_LIBS=ON \
+    -DBUILD_STATIC_LIBS=ON \
+    -DBUILD_gflags_LIB=ON
+}
+
 function install_velox_deps {
   run_and_time install_velox_deps_from_apt
+  run_and_time install_gflags
   run_and_time install_fmt
   run_and_time install_protobuf
   run_and_time install_grpc
   run_and_time install_boost
   run_and_time install_fast_float
   run_and_time install_folly

Why this ordering matters

Folly's installed cmake config (/usr/local/lib/cmake/folly/folly-targets.cmake) hardcodes the gflags library path at the time Folly is built. If install_gflags runs first and installs a PIC-compiled libgflags.a to /usr/local/lib, Folly will link against that version and export the correct path in its cmake targets. The subsequent libvelox.so link then resolves gflags_static to the PIC library and succeeds.

Note on libgoogle-glog-dev

libgoogle-glog-dev has libgflags-dev as an apt dependency. After the apt-get remove in install_gflags, glog headers (glog/logging.h) may be missing if they were only pulled in transitively. The existing libgoogle-glog-dev in install_velox_deps_from_apt (line 111) runs before install_gflags, so the headers are present during compilation. However, the apt-get remove in install_gflags may pull glog-dev out as well depending on apt's dependency resolution. A safe guard is to re-install it after:

 function install_gflags {
   ${SUDO} apt-get remove -y libgflags-dev || true
   wget_and_untar https://github.com/gflags/gflags/archive/v2.2.2.tar.gz gflags
   cmake_install_dir gflags \
     -DCMAKE_POSITION_INDEPENDENT_CODE=ON \
     -DBUILD_SHARED_LIBS=ON \
     -DBUILD_STATIC_LIBS=ON \
     -DBUILD_gflags_LIB=ON
+  # Reinstall glog-dev in case apt removed it as a side effect of removing libgflags-dev
+  ${SUDO} apt-get install -y libgoogle-glog-dev
 }