Re: [PATCH 1/1] tools build: Fix llvm feature detection, still used by bpftool

[Ian Rogers <irogers@google.com>]

On Thu, Oct 19, 2023 at 2:17 PM Arnaldo Carvalho de Melo
<acme@kernel.org> wrote:
>
> When removing the BPF event for perf a feature test that checks if the
> llvm devel files are availabe was removed but that is also used by
> bpftool.
>
> bpftool uses it to decide what kind of disassembly it will use: llvm or
> binutils based.
>
> Removing the tools/build/feature/test-llvm.cpp file made bpftool to
> always fallback to binutils disassembly, even with the llvm devel files
> installed, fix it by restoring just that small test-llvm.cpp test file.
>
> Fixes: 56b11a2126bf2f42 ("perf bpf: Remove support for embedding clang for compiling BPF events (-e foo.c)")
> Reported-by: Manu Bretelle <chantr4@gmail.com>
> Cc: Adrian Hunter <adrian.hunter@intel.com>
> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Cc: Andi Kleen <ak@linux.intel.com>
> Cc: Andrii Nakryiko <andrii@kernel.org>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Cc: Carsten Haitzler <carsten.haitzler@arm.com>
> Cc: Eduard Zingerman <eddyz87@gmail.com>
> Cc: Fangrui Song <maskray@google.com>
> Cc: He Kuang <hekuang@huawei.com>
> Cc: Ian Rogers <irogers@google.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: James Clark <james.clark@arm.com>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: Kan Liang <kan.liang@linux.intel.com>
> Cc: Leo Yan <leo.yan@linaro.org>
> Cc: llvm@lists.linux.dev
> Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Nathan Chancellor <nathan@kernel.org>
> Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Quentin Monnet <quentin@isovalent.com>
> Cc: Ravi Bangoria <ravi.bangoria@amd.com>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
> Cc: Tom Rix <trix@redhat.com>
> Cc: Wang Nan <wangnan0@huawei.com>
> Cc: Wang ShaoBo <bobo.shaobowang@huawei.com>
> Cc: Yang Jihong <yangjihong1@huawei.com>
> Cc: Yonghong Song <yhs@fb.com>
> Cc: YueHaibing <yuehaibing@huawei.com>
> Link: https://lore.kernel.org/lkml/ZTGa0Ukt7QyxWcVy@kernel.org
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Sorry for the breakage.

Reviewed-by: Ian Rogers <irogers@google.com>

Thanks,
Ian

> ---
>  tools/build/feature/test-llvm.cpp | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>  create mode 100644 tools/build/feature/test-llvm.cpp
>
> diff --git a/tools/build/feature/test-llvm.cpp b/tools/build/feature/test-llvm.cpp
> new file mode 100644
> index 0000000000000000..88a3d1bdd9f6978e
> --- /dev/null
> +++ b/tools/build/feature/test-llvm.cpp
> @@ -0,0 +1,14 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "llvm/Support/ManagedStatic.h"
> +#include "llvm/Support/raw_ostream.h"
> +#define NUM_VERSION (((LLVM_VERSION_MAJOR) << 16) + (LLVM_VERSION_MINOR << 8) + LLVM_VERSION_PATCH)
> +
> +#if NUM_VERSION < 0x030900
> +# error "LLVM version too low"
> +#endif
> +int main()
> +{
> +       llvm::errs() << "Hello World!\n";
> +       llvm::llvm_shutdown();
> +       return 0;
> +}
> --
> 2.41.0
>