From e97134841409b48fbf13401273bde9769746120f Mon Sep 17 00:00:00 2001
From: Patrick Kopper <patrick.kopper@cern.ch>
Date: Tue, 25 Aug 2026 15:14:54 +0200
Subject: [PATCH] nvcc: Allow host compiler different to CXX

CUDA uses the environment variable `NVCC_CCBIN` to specify the host compiler used by nvcc, e.g., in case of an incompatible system GCC version. Respect this variable in the Makefile.
---
 Makefile | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 17b5e8a31..831b97a1e 100644
--- a/Makefile
+++ b/Makefile
@@ -35,10 +35,13 @@ HOST_CXXFLAGS := -O2 -fPIC -fdiagnostics-show-option -felide-constructors -fmess
 # Compiler flags supported by GCC but not by the LLVM-based compilers (clang, hipcc, icpx, etc.)
 LLVM_UNSUPPORTED_CXXFLAGS := --param vect-max-version-for-alias-checks=50 -Werror=format-contains-nul -Wno-non-template-friend -Werror=return-local-addr -Werror=unused-but-set-variable
 
+# In case nvcc uses a different compiler than CXX
+CUDA_NVCC_HOST_COMPILER := $(if $(NVCC_CCBIN),$(NVCC_CCBIN),$(CXX))
+
 export CXXFLAGS := -std=c++20 $(HOST_CXXFLAGS) $(USER_CXXFLAGS) -g
 export NVCXX_CXXFLAGS := -std=c++20 -O0 -cuda -gpu=managed -stdpar -fpic -gopt $(USER_CXXFLAGS)
 export LDFLAGS := -O2 -fPIC -pthread -Wl,-E -lstdc++fs -ldl
-export LDFLAGS_NVCC := -ccbin $(CXX) --linker-options '-E' --linker-options '-lstdc++fs'
+export LDFLAGS_NVCC := -ccbin $(CUDA_NVCC_HOST_COMPILER) --linker-options '-E' --linker-options '-lstdc++fs'
 export LDFLAGS_NVCXX := -cuda -Wl,-E -ldl -gpu=managed -stdpar
 export SO_LDFLAGS := -Wl,-z,defs
 export SO_LDFLAGS_NVCC := --linker-options '-z,defs'
@@ -87,7 +90,7 @@ CUDA_DEBUG_FLAGS := --generate-line-info --source-in-ptx
 endif
 define CUFLAGS_template
 $(2)NVCC_FLAGS := $$(foreach ARCH,$(1),-gencode arch=compute_$$(ARCH),code=[sm_$$(ARCH),compute_$$(ARCH)]) -Wno-deprecated-gpu-targets -Xcudafe --diag_suppress=esa_on_defaulted_function_ignored --expt-relaxed-constexpr --expt-extended-lambda $(CUDA_DEBUG_FLAGS) --display-error-number --threads $$(words $(1)) --cudart=shared
-$(2)NVCC_COMMON := -std=c++20 -O3 -g $$($(2)NVCC_FLAGS) -ccbin $(CXX) --compiler-options '$(HOST_CXXFLAGS) $(USER_CXXFLAGS)'
+$(2)NVCC_COMMON := -std=c++20 -O3 -g $$($(2)NVCC_FLAGS) -ccbin $(CUDA_NVCC_HOST_COMPILER) --compiler-options '$(HOST_CXXFLAGS) $(USER_CXXFLAGS)'
 $(2)CUDA_CUFLAGS := -dc $$($(2)NVCC_COMMON) $(USER_CUDAFLAGS)
 $(2)CUDA_DLINKFLAGS := -dlink $$($(2)NVCC_COMMON)
 endef