Re: [PATCH bpf-next v2] bpftool: fix linkage with statically built libllvm

[sdf@google.com]

On 12/22, 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 shared libllvm library is  
> 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)'
>      ...

> So in the case of static libllvm we need to explicitly link bpftool with
> required libraries, namely, libstdc++ and those provided by the  
> `llvm-config
> --system-libs` command.  We can distinguish between the shared and static  
> cases
> by using the `llvm-config --shared-mode` command.

> eb9d1acf634b commit ("bpftool: Add LLVM as default library for  
> disassembling JIT-ed programs")
> Signed-off-by: Anton Protopopov <aspsk@isovalent.com>

Acked-by: Stanislav Fomichev <sdf@google.com>

Thank you!

> ---
> v2:
>    Use llvm-config to distinguish between shared and static modes  
> (Stanislav)

>   tools/bpf/bpftool/Makefile | 4 ++++
>   1 file changed, 4 insertions(+)

> diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
> index 313fd1b09189..ab20ecc5acce 100644
> --- a/tools/bpf/bpftool/Makefile
> +++ b/tools/bpf/bpftool/Makefile
> @@ -145,6 +145,10 @@ ifeq ($(feature-llvm),1)
>     LLVM_CONFIG_LIB_COMPONENTS := mcdisassembler all-targets
>     CFLAGS  += $(shell $(LLVM_CONFIG) --cflags --libs  
> $(LLVM_CONFIG_LIB_COMPONENTS))
>     LIBS    += $(shell $(LLVM_CONFIG) --libs $(LLVM_CONFIG_LIB_COMPONENTS))
> +  ifeq ($(shell $(LLVM_CONFIG) --shared-mode),static)
> +    LIBS += $(shell $(LLVM_CONFIG) --system-libs  
> $(LLVM_CONFIG_LIB_COMPONENTS))
> +    LIBS += -lstdc++
> +  endif
>     LDFLAGS += $(shell $(LLVM_CONFIG) --ldflags)
>   else
>     # Fall back on libbfd
> --
> 2.34.1