Re: [PATCH bpf-next] bpftool: fix linkage with statically built libllvm

[sdf@google.com]

On 12/21, Anton Protopopov wrote:
> Since the eb9d1acf634b commit ("bpftool: Add LLVM as default library for
> disassembling JIT-ed programs") we might link the bpftool program with the
> libllvm library.  This works fine when a dynamically built libllvm  
> available,
> but fails if we want to link bpftool with a statically built llvm:

>      /usr/bin/ld:  
> /usr/local/lib/libLLVMSupport.a(CrashRecoveryContext.cpp.o): in function  
> `llvm::CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup()':
>       
> CrashRecoveryContext.cpp:(.text._ZN4llvm27CrashRecoveryContextCleanupD0Ev+0x17):  
> undefined reference to `operator delete(void*, unsigned long)'
>      /usr/bin/ld:  
> /usr/local/lib/libLLVMSupport.a(CrashRecoveryContext.cpp.o): in function  
> `llvm::CrashRecoveryContext::~CrashRecoveryContext()':
>       
> CrashRecoveryContext.cpp:(.text._ZN4llvm20CrashRecoveryContextD2Ev+0xc8):  
> undefined reference to `operator delete(void*, unsigned long)'
>      ...

> To fix this we need to explicitly link bpftool with required libraries,  
> namely,
> libstdc++ and those provided by `llvm-config --system-libs`.  This patch
> doesn't change the build with a dynamically built libllvm, as the  
> `llvm-config
> --system-libs` list is empty in this case, and the bpftool is linked with  
> the
> libstdc++ in any case as this is a dynamic dependency of libLLVM.so.

> eb9d1acf634b commit ("bpftool: Add LLVM as default library for  
> disassembling JIT-ed programs")
> Signed-off-by: Anton Protopopov <aspsk@isovalent.com>
> ---
>   tools/bpf/bpftool/Makefile | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

> diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
> index 787b857d3fb5..e4c15095eac7 100644
> --- a/tools/bpf/bpftool/Makefile
> +++ b/tools/bpf/bpftool/Makefile
> @@ -144,7 +144,7 @@ ifeq ($(feature-llvm),1)
>     CFLAGS  += -DHAVE_LLVM_SUPPORT
>     LLVM_CONFIG_LIB_COMPONENTS := mcdisassembler all-targets
>     CFLAGS  += $(shell $(LLVM_CONFIG) --cflags --libs  
> $(LLVM_CONFIG_LIB_COMPONENTS))
> -  LIBS    += $(shell $(LLVM_CONFIG) --libs $(LLVM_CONFIG_LIB_COMPONENTS))
> +  LIBS    += $(shell $(LLVM_CONFIG) --libs --system-libs  
> $(LLVM_CONFIG_LIB_COMPONENTS)) -lstdc++


Why not do separate lines? We can then maybe do a bit safer approach?

LIBS += $(shell $(LLVM_CONFIG) --libs $(LLVM_CONFIG_LIB_COMPONENTS))
ifeq ($(USE_STATIC_COMPONENTS), static)
LIBS += $(shell $(LLVM_CONFIG) --system-libs))
LIBS += -lstdc++
endif

Can we use `llvm-config --shared-mode` to get USE_STATIC_COMPONENTS?

>     LDFLAGS += $(shell $(LLVM_CONFIG) --ldflags)
>   else
>     # Fall back on libbfd
> --
> 2.34.1