Re: [PATCH v1 1/4] perf parse-events: Remove BPF event support

From: Manu Bretelle
Date: Thu Oct 19 2023 - 18:50:53 EST

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On Thu, Oct 19, 2023 at 06:08:33PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Thu, Oct 19, 2023 at 12:45:08PM -0700, Manu Bretelle escreveu:
> > cc @quentin
> >
> > On Fri, Aug 11, 2023 at 12:41:36PM -0300, Arnaldo Carvalho de Melo wrote:
> > > Em Fri, Aug 11, 2023 at 11:43:22AM -0300, Arnaldo Carvalho de Melo escreveu:
> > > > Right now it is not applying due to some clash with other changes and
> > > > when I tried to apply it manually there were some formatting issues:
> > > >
> > > > ⬢[acme@toolbox perf-tools-next]$ head ~/wb/1.patch
> > > > From SRS0=EALy=D3=flex--irogers.bounces.google.com=3IDHVZAcKBAUnwtljwxlttlqj.htrfhrjpjwsjq.twl@xxxxxxxxxx Thu Aug 10 17:53:46 2023
> > > > Delivered-To: arnaldo.melo@xxxxxxxxx
> > > > Received: from imap.gmail.com [64.233.186.109]
> > > > by quaco with IMAP (fetchmail-6.4.37)
> > > > for <acme@localhost> (single-drop); Thu, 10 Aug 2023 17:53:46 -0300 (-03)
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> > > > h15-20020a4a6b4f000000b0056cb2ab9820mr2695332oof.8.1691693392493; Thu, 10 Aug
> > > > ⬢[acme@toolbox perf-tools-next]$ patch -p1 < ~/wb/1.patch
> > > > patching file tools/perf/Documentation/perf-config.txt
> > > > patch: **** malformed patch at line 234: ith
> > > >
> > > > ⬢[acme@toolbox perf-tools-next]$
> > > >
> > > > I'm trying to apply it manually.
> > >
> > > I have this extracted from this patch as the first patch in the series:
> > >
> > > >From adc61b5774a9de62f34d593f164ca02daa6fb44c Mon Sep 17 00:00:00 2001
> > > From: Ian Rogers <irogers@xxxxxxxxxx>
> > > Date: Fri, 11 Aug 2023 12:19:48 -0300
> > > Subject: [PATCH 1/1] perf bpf: Remove support for embedding clang for
> > > compiling BPF events (-e foo.c)
> > >
> > > This never was in the default build for perf, is difficult to maintain
> > > as it uses clang/llvm internals so ditch it, keeping, for now, the
> > > external compilation of .c BPF into .o bytecode and its subsequent
> > > loading, that is also going to be removed, do it separately to help
> > > bisection and to properly document what is being removed and why.
> > >
> > > Committer notes:
> > >
> > > Extracted from a larger patch and removed some leftovers, namely
> > > deleting these now unused feature tests:
> > >
> > > tools/build/feature/test-clang.cpp
> > > tools/build/feature/test-cxx.cpp
> > > tools/build/feature/test-llvm-version.cpp
> > > tools/build/feature/test-llvm.cpp
> > >
> >
> > This seem to have broken `llvm` feature detection for `bpftool`.
> >
> > The feature detections are still available in `tools/build/Makefile.feature` [0]
> > but the .cpp files are gone.
> >
> > `bpftool` still rely on the `llvm` feature:
> >
> > $ git --no-pager grep 'feature-llvm'
> > tools/bpf/bpftool/Makefile:ifeq ($(feature-llvm),1)
> >
> > The result of testing llvm feature is:
> >
> > $ cat tools/build/feature/test-llvm.make.output
> > cc1plus: fatal error: test-llvm.cpp: No such file or directory
> > compilation terminated.
> >
> > With current head:
> >
> > make -j $((4*$(nproc))) -C tools/bpf/bpftool && ./tools/bpf/bpftool/bpftool --version
> > ...
> > Auto-detecting system features:
> > ... clang-bpf-co-re: [ on ]
> > ... llvm: [ OFF ]
> > ... libcap: [ on ]
> > ... libbfd: [ on ]
> > ...
> > ...
> > ...
> > bpftool v7.3.0
> > using libbpf v1.3
> > features: libbfd, skeletons
> >
> > After applying
> >
> > git show 56b11a2126bf2f422831ecf6112b87a4485b221b tools/build/feature | \
> > patch -p1 -R
>
>
> Ouch, so probably we need just to reintroduce that one
> tools/build/feature/test-llvm.cpp file.

Yes, I believe so. From git-grepping `feature-<feature>`, only `feature-llvm` came up.

I suppose as part of the cleanup the features should have been
removed from tools/build/Makefile.feature too.

>
> Building perf these days ends up using bpftool, and the end result as
> noticed with me testing perf, perf trace with bpf, etc didn't change, so
> I didn't notice :-\
>
> And:
>
> ifeq ($(feature-llvm),1)
> # If LLVM is available, use it for JIT disassembly
> CFLAGS += -DHAVE_LLVM_SUPPORT
> LLVM_CONFIG_LIB_COMPONENTS := mcdisassembler all-targets
> CFLAGS += $(shell $(LLVM_CONFIG) --cflags --libs $(LLVM_CONFIG_LIB_COMPONENTS))
> LIBS += $(shell $(LLVM_CONFIG) --libs $(LLVM_CONFIG_LIB_COMPONENTS))
> ifeq ($(shell $(LLVM_CONFIG) --shared-mode),static)
> LIBS += $(shell $(LLVM_CONFIG) --system-libs $(LLVM_CONFIG_LIB_COMPONENTS))
> LIBS += -lstdc++
> endif
> LDFLAGS += $(shell $(LLVM_CONFIG) --ldflags)
> else
> # Fall back on libbfd
> ifeq ($(feature-libbfd),1)
> LIBS += -lbfd -ldl -lopcodes
> else ifeq ($(feature-libbfd-liberty),1)
> LIBS += -lbfd -ldl -lopcodes -liberty
> else ifeq ($(feature-libbfd-liberty-z),1)
> LIBS += -lbfd -ldl -lopcodes -liberty -lz
> endif
>
> # If one of the above feature combinations is set, we support libbfd
> ifneq ($(filter -lbfd,$(LIBS)),)
> CFLAGS += -DHAVE_LIBBFD_SUPPORT
>
> # Libbfd interface changed over time, figure out what we need
> ifeq ($(feature-disassembler-four-args), 1)
> CFLAGS += -DDISASM_FOUR_ARGS_SIGNATURE
> endif
> ifeq ($(feature-disassembler-init-styled), 1)
> CFLAGS += -DDISASM_INIT_STYLED
> endif
> endif
> endif
>
> And there is a fallback to using binutils, so most people ended up not
> noticing.

Yes, definitely, the fallback make it harder to easily detect.
I detected it because I was manually building bpftool and it was odd that llvm
was not detected.

>
> I wonder how to improve the current situation to detect these kinds of
> problems in the future, i.e. how to notice that some file needed by some
> Makefile, etc got removed or that some feature test fails because some
> change in the test .c files makes them fail and thus activates fallbacks
> like the one above :-\

I think it is tricky. Specifically to this situation, some CI could try to build
the different combinaison of bpftool and check the features through the build
`bpftool --version`.
This is actually a test that I run internally to make sure our build has some
feature enabled.
This is actually tested by bpftool in the GH CI:
https://github.com/libbpf/bpftool/blob/main/.github/workflows/build.yaml#L62

As a matter of fact, it would not have been detected because that CI uses a
different Makefile.feature.

Quentin and I were talking offline how we could improve bpftool CI at diff time.
This is an example where it would have helped :)

>
>
> So if I just get this back:
>
> ⬢[acme@toolbox perf-tools-next]$ cat tools/build/feature/test-llvm.cpp
> // 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;
> }
> ⬢[acme@toolbox perf-tools-next]$
>
> And install the llvm-devel package then it back working:
>
> ⬢[acme@toolbox perf-tools-next]$ make -C tools/bpf/bpftool
> make: Entering directory '/home/acme/git/perf-tools-next/tools/bpf/bpftool'
>
> Auto-detecting system features:
> ... clang-bpf-co-re: [ on ]
> ... llvm: [ on ]
> ... libcap: [ on ]
> ... libbfd: [ on ]
> <SNIP>
> ⬢[acme@toolbox perf-tools-next]$ cat tools/build/feature/test-llvm.make.output
> ⬢[acme@toolbox perf-tools-next]$ ls -la tools/build/feature/test-llvm.
> test-llvm.bin test-llvm.cpp test-llvm.d test-llvm.make.output
> ⬢[acme@toolbox perf-tools-next]$ ls -la tools/build/feature/test-llvm.bin
> -rwxr-xr-x. 1 acme acme 17712 Oct 19 18:04 tools/build/feature/test-llvm.bin
> ⬢[acme@toolbox perf-tools-next]$ ldd tools/build/feature/test-llvm.bin
> linux-vdso.so.1 (0x00007ffcaf5d9000)
> libLLVM-16.so => /lib64/libLLVM-16.so (0x00007fc4faefa000)
> libstdc++.so.6 => /lib64/libstdc++.so.6 (0x00007fc4faca6000)
> libm.so.6 => /lib64/libm.so.6 (0x00007fc4fabc5000)
> libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007fc4faba1000)
> libc.so.6 => /lib64/libc.so.6 (0x00007fc4fa9c3000)
> libffi.so.8 => /lib64/libffi.so.8 (0x00007fc4fa9b7000)
> libedit.so.0 => /lib64/libedit.so.0 (0x00007fc4fa978000)
> libz.so.1 => /lib64/libz.so.1 (0x00007fc4fa95e000)
> libtinfo.so.6 => /lib64/libtinfo.so.6 (0x00007fc4fa92b000)
> /lib64/ld-linux-x86-64.so.2 (0x00007fc502404000)
> ⬢[acme@toolbox perf-tools-next]$ sudo dnf install llvm-devel
>
> I'll get this merged in my perf-tools-fixes-for-v6.6 that I'll submit
> tomorrow to Linus, thanks for reporting!
>
> I'll add your:
>
> Reported-by: Manu Bretelle <chantr4@xxxxxxxxx>
>
> And:
>
> Fixes: 56b11a2126bf2f42 ("perf bpf: Remove support for embedding clang for compiling BPF events (-e foo.c)")
>
> Ok?

SGTM. Thanks for the quick turnaround.

Reviewed-by: Manu Bretelle <chantr4@xxxxxxxxx>

>
> - Arnaldo

Next message: Quentin Monnet: "Re: [PATCH 1/1] tools build: Fix llvm feature detection, still used by bpftool"
Previous message: Jeff Layton: "Re: [PATCH RFC 2/9] timekeeping: new interfaces for multigrain timestamp handing"
In reply to: Ian Rogers: "Re: [PATCH v1 1/4] perf parse-events: Remove BPF event support"
Next in thread: Arnaldo Carvalho de Melo: "Re: [PATCH v1 1/4] perf parse-events: Remove BPF event support"
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