Re: [PATCH 2/2] perf clang: Fixes for more recent LLVM/clang

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Fri, Nov 12, 2021 at 06:24:44PM +0800, Ma Xinjian escreveu:
> Hi
> 
> We build perf with clang also recently, but unlucky that failed with
> following errors:
> 
> 
> ```
> In file included from /usr/lib/llvm-7/include/llvm/ADT/STLExtras.h:21,
>                  from /usr/lib/llvm-7/include/llvm/ADT/StringRef.h:13,
>                  from /usr/lib/llvm-7/include/clang/Basic/Version.h:20,
>                  from test-clang.cpp:2:
> /usr/lib/llvm-7/include/llvm/ADT/SmallVector.h: In instantiation of 'void
> llvm::SmallVectorTemplateBase<T, true>::push_back(const T&) [with T =
> clang::driver::OffloadUnbundlingJobAction::DependentActionInfo]':
> /usr/lib/llvm-7/include/clang/Driver/Action.h:579:61:   required from here
> /usr/lib/llvm-7/include/llvm/ADT/SmallVector.h:313:11: error: 'void*
> memcpy(void*, const void*, size_t)' writing to an object of type 'struct
> clang::driver::OffloadUnbundlingJobAction::DependentActionInfo' with no
> trivial copy-assignment; use copy-initialization instead
> [-Werror=class-memaccess]
>      memcpy(this->end(), &Elt, sizeof(T));
>      ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> In file included from /usr/lib/llvm-7/include/clang/Driver/Driver.h:15,
>                  from test-clang.cpp:6:
> /usr/lib/llvm-7/include/clang/Driver/Action.h:549:10: note: 'struct
> clang::driver::OffloadUnbundlingJobAction::DependentActionInfo' declared
> here
>    struct DependentActionInfo final {
>           ^~~~~~~~~~~~~~~~~~~
> cc1plus: all warnings being treated as errors
> ```
> 
> llvm version: 7
> rootfs: Debian10
> kernel: v5.8 v5.11 v5.15
> reproduce:
> $ cd linux/tools/perf
> $ make LIBCLANGLLVM=1 ARCH= EXTRA_CFLAGS='-fno-omit-frame-pointer
> -fsanitize=undefined -fsanitize=address'
> 
> Would you please kindly point out what's wrong with our steps? Or can you
> give us your command to make perf with clang?

This is just for building it with clang embedded, is that strictly
required?

I.e. you can still use perf to build bpf by calling clang, etc.

Or are you trying to _build_ perf using clang?

To build perf with clang:

⬢[acme@toolbox perf]$ rm -rf /tmp/build/perf ; mkdir -p /tmp/build/perf ; 
⬢[acme@toolbox perf]$ make -C tools/perf CC=clang O=/tmp/build/perf

End result:

⬢[acme@toolbox perf]$ perf -v
perf version 5.15.gf8b114cfd541

⬢[acme@toolbox perf]$ readelf -wi /tmp/build/perf/perf | grep -m5 DW_AT_producer
    <c>   DW_AT_producer    : (indirect string, offset: 0x0): clang version 13.0.0 (https://github.com/llvm/llvm-project e8991caea8690ec2d17b0b7e1c29bf0da6609076)
    <a6b>   DW_AT_producer    : (indirect string, offset: 0x0): clang version 13.0.0 (https://github.com/llvm/llvm-project e8991caea8690ec2d17b0b7e1c29bf0da6609076)
    <76f0>   DW_AT_producer    : (indirect string, offset: 0x0): clang version 13.0.0 (https://github.com/llvm/llvm-project e8991caea8690ec2d17b0b7e1c29bf0da6609076)
    <823d>   DW_AT_producer    : (indirect string, offset: 0x0): clang version 13.0.0 (https://github.com/llvm/llvm-project e8991caea8690ec2d17b0b7e1c29bf0da6609076)
    <121a8>   DW_AT_producer    : (indirect string, offset: 0x0): clang version 13.0.0 (https://github.com/llvm/llvm-project e8991caea8690ec2d17b0b7e1c29bf0da6609076)
⬢[acme@toolbox perf]$

- Arnaldo