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[LLVM] Check if zstd static libraries are built with -fPIC flag #15970

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[LLVM] Check if zstd static libraries are built with -fPIC flag #15970

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37 changes: 36 additions & 1 deletion llvm/cmake/config-ix.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -167,7 +167,42 @@ if(LLVM_USE_STATIC_ZSTD AND NOT TARGET zstd::libzstd_static)
endif()
set(LLVM_ENABLE_ZSTD OFF)
else()
set(LLVM_ENABLE_ZSTD ${zstd_FOUND})
# Check if the zstd static library is usable when BUILD_SHARED_LIBS is ON
# Test linking zstd::libzstd_static with a shared library. This is to ensure
# that the static library is built with -fPIC flag.
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i havent seen this kind of issue before, is that because almost everything is built with -fPIC so it just works?

are there any other examples in llvm or other open source projects of solving it this way?

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i havent seen this kind of issue before, is that because almost everything is built with -fPIC so it just works?

This issue was observed when DPC++ is built in shared lib configuration on Ubuntu 24.04. Apparently, the zstd static library that comes with Ubuntu 24.04 was built without the -fPIC flag and thus it gives error when linking to dynamic libraries. I've filed a bug report about the zstd package in Ubuntu 24.04 here: https://bugs.launchpad.net/ubuntu/+source/libzstd/+bug/2086543

We did not observe this error before because the zstd package that we use in CI (Ubuntu 22.04) was built correctly with fPIC flag.

are there any other examples in llvm or other open source projects of solving it this way?

I'm not aware of any. Let me dig around.

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@sarnex sarnex Nov 4, 2024 •
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yeah my overalll question is i've never seen this kind of issue before so i don't know what the fix should look like so i can't give a good review :)

if(zstd_FOUND AND LLVM_USE_STATIC_ZSTD AND TARGET zstd::libzstd_static AND BUILD_SHARED_LIBS)
cmake_push_check_state()

set(CMAKE_REQUIRED_FLAGS "-fPIC -shared")
set(CMAKE_REQUIRED_INCLUDES ${ZSTD_INCLUDE_DIRS})
set(CMAKE_REQUIRED_LIBRARIES zstd::libzstd_static)
check_c_source_compiles("
#include <zstd.h>
int main() {
ZSTD_CCtx* cctx = ZSTD_createCCtx();
ZSTD_freeCCtx(cctx);
return 0;
}"
IS_ZSTD_STATIC_LIB_USABLE_WITH_SHARED_LIBRARIES
OUTPUT_VARIABLE CMAKE_ERROR_MESSAGE)

cmake_pop_check_state()

# If the test program failed to compile, disable zstd or fail if LLVM_ENABLE_ZSTD is FORCE_ON.
if(NOT IS_ZSTD_STATIC_LIB_USABLE_WITH_SHARED_LIBRARIES)
message(WARNING "ZSTD static library is not usable. Error compiling the test program.")
message(WARNING "Build log:\n ${CMAKE_ERROR_MESSAGE}")

# Fail if LLVM_ENABLE_ZSTD is FORCE_ON.
if(LLVM_ENABLE_ZSTD STREQUAL FORCE_ON)
message(FATAL_ERROR "zstd static library is not usable, but LLVM_USE_STATIC_ZSTD=ON and LLVM_ENABLE_ZSTD=FORCE_ON.")
endif()
endif()

set(LLVM_ENABLE_ZSTD IS_ZSTD_STATIC_LIB_USABLE_WITH_SHARED_LIBRARIES)
else()
set(LLVM_ENABLE_ZSTD ${zstd_FOUND})
endif()
endif()

if(LLVM_ENABLE_LIBXML2)
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