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

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Date:   Fri, 12 Nov 2021 15:43:58 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ma Xinjian <xinjianx.ma@...el.com>
Cc:     irogers@...gle.com, alexander.shishkin@...ux.intel.com,
        daniel@...earbox.net, jolsa@...hat.com, leo.yan@...aro.org,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        llvm@...ts.linux.dev, mark.rutland@....com, mingo@...hat.com,
        mpetlan@...hat.com, namhyung@...nel.org, nathan@...nel.org,
        ndesaulniers@...gle.com, peterz@...radead.org,
        sedat.dilek@...il.com, philip.li@...el.com
Subject: Re: [PATCH 2/2] perf clang: Fixes for more recent LLVM/clang

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

End result:

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

⬢[acme@...lbox 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@...lbox perf]$

- Arnaldo