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fix(cmake): verify CBLAS symbols link, not just that cblas.h exists #257

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Merged
cjpais merged 1 commit into from
Nov 11, 2026
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fix(cmake): verify CBLAS symbols link, not just that cblas.h exists #257

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57 changes: 48 additions & 9 deletions src/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -225,18 +225,57 @@ elseif(TRANSCRIBE_USE_SYSTEM_BLAS)
# (e.g. -DBLA_VENDOR=OpenBLAS). find_package probes the system.
find_package(BLAS QUIET)
if(BLAS_FOUND)
# find_package(BLAS) may find a Fortran-only BLAS (e.g. libblas3
# on Debian/Ubuntu) that lacks the cblas C wrappers. Verify that
# cblas.h exists before enabling; otherwise the build compiles
# cblas_sgemv calls but the linker can't resolve them.
include(CheckIncludeFile)
check_include_file(cblas.h HAVE_CBLAS_H)
# find_package(BLAS) may find a Fortran-only BLAS that lacks the cblas
# C wrappers (e.g. Netlib `blas` on Arch/Fedora, where they live in a
# separate libcblas). The header can be present while the library is
# not, and a shared libtranscribe still links (undefined symbols are
# allowed), then dies at runtime with "undefined symbol: cblas_sgemm".
# So check that the symbols actually link, not just that cblas.h exists.
# OpenBLAS on Arch (blas-openblas) and Fedora (openblas-devel) puts
# cblas.h under include/openblas/, off the default search path.
include(CheckSymbolExists)
include(CMakePushCheckState)
find_path(TRANSCRIBE_CBLAS_INCLUDE_DIR cblas.h PATH_SUFFIXES openblas)
if(TRANSCRIBE_CBLAS_INCLUDE_DIR)
set(HAVE_CBLAS_H TRUE)
else()
set(HAVE_CBLAS_H FALSE)
endif()
set(_transcribe_cblas_libs "")
if(HAVE_CBLAS_H)
target_link_libraries(transcribe PRIVATE ${BLAS_LIBRARIES})
cmake_push_check_state(RESET)
set(CMAKE_REQUIRED_INCLUDES ${TRANSCRIBE_CBLAS_INCLUDE_DIR})
set(CMAKE_REQUIRED_LIBRARIES ${BLAS_LIBRARIES})
check_symbol_exists(cblas_sgemm "cblas.h" TRANSCRIBE_BLAS_HAS_CBLAS_SGEMM)
check_symbol_exists(cblas_sgemv "cblas.h" TRANSCRIBE_BLAS_HAS_CBLAS_SGEMV)
cmake_pop_check_state()
if(TRANSCRIBE_BLAS_HAS_CBLAS_SGEMM AND TRANSCRIBE_BLAS_HAS_CBLAS_SGEMV)
set(_transcribe_cblas_libs ${BLAS_LIBRARIES})
else()
# Fortran-only BLAS: try the separate reference CBLAS library.
find_library(TRANSCRIBE_CBLAS_LIBRARY NAMES cblas)
if(TRANSCRIBE_CBLAS_LIBRARY)
cmake_push_check_state(RESET)
set(CMAKE_REQUIRED_INCLUDES ${TRANSCRIBE_CBLAS_INCLUDE_DIR})
set(CMAKE_REQUIRED_LIBRARIES ${TRANSCRIBE_CBLAS_LIBRARY} ${BLAS_LIBRARIES})
check_symbol_exists(cblas_sgemm "cblas.h" TRANSCRIBE_LIBCBLAS_HAS_CBLAS_SGEMM)
check_symbol_exists(cblas_sgemv "cblas.h" TRANSCRIBE_LIBCBLAS_HAS_CBLAS_SGEMV)
cmake_pop_check_state()
if(TRANSCRIBE_LIBCBLAS_HAS_CBLAS_SGEMM AND TRANSCRIBE_LIBCBLAS_HAS_CBLAS_SGEMV)
set(_transcribe_cblas_libs ${TRANSCRIBE_CBLAS_LIBRARY} ${BLAS_LIBRARIES})
endif()
endif()
endif()
endif()
if(_transcribe_cblas_libs)
target_include_directories(transcribe PRIVATE ${TRANSCRIBE_CBLAS_INCLUDE_DIR})
target_link_libraries(transcribe PRIVATE ${_transcribe_cblas_libs})
target_compile_definitions(transcribe PRIVATE TRANSCRIBE_HAS_BLAS=1)
message(STATUS "transcribe: BLAS found — decoder will use cblas_sgemv")
message(STATUS "transcribe: CBLAS found (${_transcribe_cblas_libs}) — decoder will use cblas_sgemm/cblas_sgemv")
elseif(NOT HAVE_CBLAS_H)
message(STATUS "transcribe: BLAS found but cblas.h missing — decoder uses scalar fallback (install OpenBLAS)")
else()
message(STATUS "transcribe: BLAS found but cblas.h missing — decoder uses scalar fallback (install libopenblas-dev)")
message(WARNING "transcribe: BLAS found (${BLAS_LIBRARIES}) but it does not provide cblas_sgemm/cblas_sgemv — decoder uses scalar fallback (install OpenBLAS or pass -DBLA_VENDOR=OpenBLAS)")
endif()
else()
message(STATUS "transcribe: no BLAS found — decoder uses scalar fallback")
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