Re: [PATCH dwarves] dwarf_loader: handle DWARF5 DW_OP_addrx properly

[Yonghong Song <yhs@fb.com>]

On 4/4/21 10:25 AM, Sedat Dilek wrote:
> On Sun, Apr 4, 2021 at 6:40 PM Yonghong Song <yhs@fb.com> wrote:
>>
>>
>>
>> On 4/4/21 5:46 AM, Sedat Dilek wrote:
[...]
>>> Next build-error:
>>>
>>> g++ -g -rdynamic -Wall -O2 -DHAVE_GENHDR
>>> -I/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf
>>> -I/home/dileks/src/linux-kernel/git/tools/testing/selftests/b
>>> pf/tools/include -I/home/dileks/src/linux-kernel/git/include/generated
>>> -I/home/dileks/src/linux-kernel/git/tools/lib
>>> -I/home/dileks/src/linux-kernel/git/tools/include
>>> -I/home/dileks/src/linux-kernel/git/tools/include/uapi
>>> -I/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf
>>> -Dbpf_prog_load=bpf_prog_test_load
>>> -Dbpf_load_program=bpf_test_load_program test_cpp.cpp
>>> /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/test_core_extern.skel.h
>>> /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/tools/build/libbpf/libbpf.a
>>> /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/test_stub.o
>>> -lcap -lelf -lz -lrt -lpthread -o
>>> /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/test_cpp
>>> /usr/bin/ld: /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/tools/build/libbpf/libbpf.a(libbpf-in.o):
>>> relocation R_X86_64_32 against `.rodata.str1.1' ca
>>> n not be used when making a PIE object; recompile with -fPIE
>>> collect2: error: ld returned 1 exit status
>>> make: *** [Makefile:455:
>>> /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/test_cpp]
>>> Error 1
>>> make: Leaving directory
>>> '/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf'
>>>
>>> LOL, I was not aware that there is usage of *** CXX*** in tools
>>> directory (see g++ line and /usr/bin/ld ?).
>>>
>>> So, I changed my $MAKE_OPTS to use "CXX=clang++".
>>
>> In kernel, if LLVM=1 is set, we have:
>>
>> ifneq ($(LLVM),)
>> HOSTCC  = clang
>> HOSTCXX = clang++
>> else
>> HOSTCC  = gcc
>> HOSTCXX = g++
>> endif
>>
>> ifneq ($(LLVM),)
>> CC              = clang
>> LD              = ld.lld
>> AR              = llvm-ar
>> NM              = llvm-nm
>> OBJCOPY         = llvm-objcopy
>> OBJDUMP         = llvm-objdump
>> READELF         = llvm-readelf
>> STRIP           = llvm-strip
>> else
>> CC              = $(CROSS_COMPILE)gcc
>> LD              = $(CROSS_COMPILE)ld
>> AR              = $(CROSS_COMPILE)ar
>> NM              = $(CROSS_COMPILE)nm
>> OBJCOPY         = $(CROSS_COMPILE)objcopy
>> OBJDUMP         = $(CROSS_COMPILE)objdump
>> READELF         = $(CROSS_COMPILE)readelf
>> STRIP           = $(CROSS_COMPILE)strip
>> endif
>>
>> So if you have right path, you don't need to set HOSTCC and HOSTCXX
>> explicitly.
>>
> 
> That is all correct with HOSTCXX but there is no CXX=... assignment
> otherwise test_cpp will use g++ as demonstrated.

This is not a kernel Makefile issue.

We have:
testing/selftests/bpf/Makefile:CXX ?= $(CROSS_COMPILE)g++

So you need to explicit add CXX=clang++ when compiling
bpf selftests with LLVM=1 LLVM_IAS=1. 


> 
>>>
>>> $ echo $PATH
>>> /opt/llvm-toolchain/bin:/opt/proxychains-ng/bin:/home/dileks/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
>>>
>>> $ echo $MAKE $MAKE_OPTS
>>> make V=1 HOSTCC=clang HOSTCXX=clang++ HOSTLD=ld.lld CC=clang
>>> CXX=clang++ LD=ld.lld LLVM=1 LLVM_IAS=1 PAHOLE=/opt/pahole/bin/pahole
>>>
>>> $ clang --version
>>> dileks clang version 12.0.0 (https://github.com/llvm/llvm-project.git
>>> 04ba60cfe598e41084fb848daae47e0ed910fa7d)
>>> Target: x86_64-unknown-linux-gnu
>>> Thread model: posix
>>> InstalledDir: /opt/llvm-toolchain/bin
>>> $ ld.lld --version
>>> LLD 12.0.0 (https://github.com/llvm/llvm-project.git
>>> 04ba60cfe598e41084fb848daae47e0ed910fa7d) (compatible with GNU
>>> linkers)
>>>
>>> $ LC_ALL=C $MAKE $MAKE_OPTS -C tools/testing/selftests/bpf/
>>>
>>> This breaks like this:
>>>
>>> clang++ -g -rdynamic -Wall -O2 -DHAVE_GENHDR
>>> -I/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf
>>> -I/home/dileks/src/linux-kernel/git/tools/testing/selftes
>>> ts/bpf/tools/include
>>> -I/home/dileks/src/linux-kernel/git/include/generated
>>> -I/home/dileks/src/linux-kernel/git/tools/lib
>>> -I/home/dileks/src/linux-kernel/git/tools/incl
>>> ude -I/home/dileks/src/linux-kernel/git/tools/include/uapi
>>> -I/home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf
>>> -Dbpf_prog_load=bpf_prog_test_load -Dbpf_loa
>>> d_program=bpf_test_load_program test_cpp.cpp
>>> /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/test_core_extern.skel.h
>>> /home/dileks/src/linux-kernel/git/to
>>> ols/testing/selftests/bpf/tools/build/libbpf/libbpf.a
>>> /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/test_stub.o
>>> -lcap -lelf -lz -lrt -lpthread -o /home
>>> /dileks/src/linux-kernel/git/tools/testing/selftests/bpf/test_cpp
>>> clang-12: warning: treating 'c-header' input as 'c++-header' when in
>>> C++ mode, this behavior is deprecated [-Wdeprecated]
>>> clang-12: error: cannot specify -o when generating multiple output files
>>> make: *** [Makefile:455:
>>> /home/dileks/src/linux-kernel/git/tools/testing/selftests/bpf/test_cpp]
>>> Error 1
>>>
>>> OK, I see in bpf-next includes several fixes like:
>>>
>>> commit a0964f526df6facd4e12a4c416185013026eecf9
>>> "selftests/bpf: Add multi-file statically linked BPF object file test"
>>>
>>> ...and to "selftests: xsk".
>>>
>>> Finally, I was able to build by suppressing the build of "test_cpp"
>>> and "xdpxceiver":
>>>
[...]
> 
> OK, I started a fresh build with LLVM/Clang v13-git from <apt.llvm.org>...
> 
> $ /usr/lib/llvm-13/bin/clang --version
> Debian clang version
> 13.0.0-++20210404092853+c4c511337247-1~exp1~20210404073605.3891
> Target: x86_64-pc-linux-gnu
> Thread model: posix
> InstalledDir: /usr/lib/llvm-13/bin
> 
> ...with latest bpf-next as new base.
> 
> I applied your/this pahole patch "[PATCH dwarves] dwarf_loader: handle
> DWARF5 DW_OP_addrx properly".
> 
> Will report later...
> 
> - Sedat -
> 
>>>
>>> [1] https://git.kernel.org/bpf/bpf-next/c/2ba4badca9977b64c966b0177920daadbd5501fe
>>> [2] https://git.kernel.org/bpf/bpf-next/c/a0964f526df6facd4e12a4c416185013026eecf9
>>>