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

[Manu Bretelle]

On Thu, Oct 19, 2023 at 06:17:37PM -0300, Arnaldo Carvalho de Melo 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@xxxxxxxxx>
> Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Cc: Andrii Nakryiko <andrii@xxxxxxxxxx>
> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> Cc: Carsten Haitzler <carsten.haitzler@xxxxxxx>
> Cc: Eduard Zingerman <eddyz87@xxxxxxxxx>
> Cc: Fangrui Song <maskray@xxxxxxxxxx>
> Cc: He Kuang <hekuang@xxxxxxxxxx>
> Cc: Ian Rogers <irogers@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: James Clark <james.clark@xxxxxxx>
> Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> Cc: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> Cc: Leo Yan <leo.yan@xxxxxxxxxx>
> Cc: llvm@xxxxxxxxxxxxxxx
> Cc: Madhavan Srinivasan <maddy@xxxxxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
> Cc: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
> Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Quentin Monnet <quentin@xxxxxxxxxxxxx>
> Cc: Ravi Bangoria <ravi.bangoria@xxxxxxx>
> Cc: Rob Herring <robh@xxxxxxxxxx>
> Cc: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
> Cc: Tom Rix <trix@xxxxxxxxxx>
> Cc: Wang Nan <wangnan0@xxxxxxxxxx>
> Cc: Wang ShaoBo <bobo.shaobowang@xxxxxxxxxx>
> Cc: Yang Jihong <yangjihong1@xxxxxxxxxx>
> Cc: Yonghong Song <yhs@xxxxxx>
> Cc: YueHaibing <yuehaibing@xxxxxxxxxx>
> Link: https://lore.kernel.org/lkml/ZTGa0Ukt7QyxWcVy@xxxxxxxxxx
> Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> ---
>  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;
> +}

Thanks for the quick turnaround!