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

Testing the use of BPF events after applying this patch:

To use the external clang/llvm toolchain to compile a .c event and then
use libbpf to load it, to get the syscalls:sys_enter_open* tracepoints
and read the filename pointer, putting it into the ring buffer right
after the usual tracepoint payload for 'perf trace' to then print it:

  [root@quaco ~]# perf trace -e /home/acme/git/perf-tools-next/tools/perf/examples/bpf/augmented_raw_syscalls.c,open* --max-events=10
     0.000 systemd-oomd/959 openat(dfd: CWD, filename: "/proc/meminfo", flags: RDONLY|CLOEXEC) = 12
     0.083 abrt-dump-jour/1453 openat(dfd: CWD, filename: "/var/log/journal/d6a97235307247e09f13f326fb607e3c/system.journal", flags: RDONLY|CLOEXEC|NONBLOCK) = 4
     0.063 abrt-dump-jour/1454 openat(dfd: CWD, filename: "/var/log/journal/d6a97235307247e09f13f326fb607e3c/system.journal", flags: RDONLY|CLOEXEC|NONBLOCK) = 4
     0.082 abrt-dump-jour/1455 openat(dfd: CWD, filename: "/var/log/journal/d6a97235307247e09f13f326fb607e3c/system.journal", flags: RDONLY|CLOEXEC|NONBLOCK) = 4
   250.124 systemd-oomd/959 openat(dfd: CWD, filename: "/proc/meminfo", flags: RDONLY|CLOEXEC) = 12
   250.521 systemd-oomd/959 openat(dfd: CWD, filename: "/sys/fs/cgroup/user.slice/user-1000.slice/[email protected]/app.slice/memory.pressure", flags: RDONLY|CLOEXEC) = 12
   251.047 systemd-oomd/959 openat(dfd: CWD, filename: "/sys/fs/cgroup/user.slice/user-1000.slice/[email protected]/app.slice/memory.current", flags: RDONLY|CLOEXEC) = 12
   251.162 systemd-oomd/959 openat(dfd: CWD, filename: "/sys/fs/cgroup/user.slice/user-1000.slice/[email protected]/app.slice/memory.min", flags: RDONLY|CLOEXEC) = 12
   251.242 systemd-oomd/959 openat(dfd: CWD, filename: "/sys/fs/cgroup/user.slice/user-1000.slice/[email protected]/app.slice/memory.low", flags: RDONLY|CLOEXEC) = 12
   251.353 systemd-oomd/959 openat(dfd: CWD, filename: "/sys/fs/cgroup/user.slice/user-1000.slice/[email protected]/app.slice/memory.swap.current", flags: RDONLY|CLOEXEC) = 12
  [root@quaco ~]#

Same thing, but with a prebuilt .o BPF bytecode:

  [root@quaco ~]# perf trace -e /home/acme/git/perf-tools-next/tools/perf/examples/bpf/augmented_raw_syscalls.o,open* --max-events=10
     0.000 systemd-oomd/959 openat(dfd: CWD, filename: "/proc/meminfo", flags: RDONLY|CLOEXEC) = 12
     0.083 abrt-dump-jour/1453 openat(dfd: CWD, filename: "/var/log/journal/d6a97235307247e09f13f326fb607e3c/system.journal", flags: RDONLY|CLOEXEC|NONBLOCK) = 4
     0.083 abrt-dump-jour/1455 openat(dfd: CWD, filename: "/var/log/journal/d6a97235307247e09f13f326fb607e3c/system.journal", flags: RDONLY|CLOEXEC|NONBLOCK) = 4
     0.062 abrt-dump-jour/1454 openat(dfd: CWD, filename: "/var/log/journal/d6a97235307247e09f13f326fb607e3c/system.journal", flags: RDONLY|CLOEXEC|NONBLOCK) = 4
   249.985 systemd-oomd/959 openat(dfd: CWD, filename: "/proc/meminfo", flags: RDONLY|CLOEXEC) = 12
   466.763 thermald/1234 openat(dfd: CWD, filename: "/sys/class/powercap/intel-rapl/intel-rapl:0/intel-rapl:0:2/energy_uj") = 13
   467.145 thermald/1234 openat(dfd: CWD, filename: "/sys/class/powercap/intel-rapl/intel-rapl:0/energy_uj") = 13
   467.311 thermald/1234 openat(dfd: CWD, filename: "/sys/class/thermal/thermal_zone2/temp") = 13
   500.040 cgroupify/24006 openat(dfd: 4, filename: ".", flags: RDONLY|CLOEXEC|DIRECTORY|NONBLOCK) = 5
   500.295 cgroupify/24006 openat(dfd: 4, filename: "24616/cgroup.procs") = 5
  [root@quaco ~]#

Signed-off-by: Ian Rogers <[email protected]>
Tested-by: Arnaldo Carvalho de Melo <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: Anshuman Khandual <[email protected]>
Cc: Athira Rajeev <[email protected]>
Cc: Brendan Gregg <[email protected]>
Cc: Carsten Haitzler <[email protected]>
Cc: Eduard Zingerman <[email protected]>
Cc: Fangrui Song <[email protected]>
Cc: He Kuang <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: James Clark <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kan Liang <[email protected]>
Cc: Leo Yan <[email protected]>
Cc: Madhavan Srinivasan <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: "Naveen N. Rao" <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ravi Bangoria <[email protected]>
Cc: Rob Herring <[email protected]>
Cc: Tiezhu Yang <[email protected]>
Cc: Tom Rix <[email protected]>
Cc: Wang Nan <[email protected]>
Cc: Wang ShaoBo <[email protected]>
Cc: Yang Jihong <[email protected]>
Cc: Yonghong Song <[email protected]>
Cc: YueHaibing <[email protected]>
Link: https://lore.kernel.org/lkml/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: captain5050

tools/build/feature/test-clang.cpp

@@ -1127,37 +1127,6 @@ ifndef NO_JVMTI
   endif
 endif
 
-USE_CXX = 0
-USE_CLANGLLVM = 0
-ifdef LIBCLANGLLVM
-  $(call feature_check,cxx)
-  ifneq ($(feature-cxx), 1)
-    msg := $(warning No g++ found, disable clang and llvm support. Please install g++)
-  else
-    $(call feature_check,llvm)
-    $(call feature_check,llvm-version)
-    ifneq ($(feature-llvm), 1)
-      msg := $(warning No suitable libLLVM found, disabling builtin clang and LLVM support. Please install llvm-dev(el) (>= 3.9.0))
-    else
-      $(call feature_check,clang)
-      ifneq ($(feature-clang), 1)
-        msg := $(warning No suitable libclang found, disabling builtin clang and LLVM support. Please install libclang-dev(el) (>= 3.9.0))
-      else
-        CFLAGS += -DHAVE_LIBCLANGLLVM_SUPPORT
-        CXXFLAGS += -DHAVE_LIBCLANGLLVM_SUPPORT -I$(shell $(LLVM_CONFIG) --includedir)
-        $(call detected,CONFIG_CXX)
-        $(call detected,CONFIG_CLANGLLVM)
-	USE_CXX = 1
-	USE_LLVM = 1
-	USE_CLANG = 1
-        ifneq ($(feature-llvm-version),1)
-          msg := $(warning This version of LLVM is not tested. May cause build errors)
-        endif
-      endif
-    endif
-  endif
-endif
-
 ifndef NO_LIBPFM4
   $(call feature_check,libpfm4)
   ifeq ($(feature-libpfm4), 1)

tools/build/feature/test-cxx.cpp

@@ -99,10 +99,6 @@ include ../scripts/utilities.mak
 # Define NO_JVMTI_CMLR (debug only) if you do not want to process CMLR
 # data for java source lines.
 #
-# Define LIBCLANGLLVM if you DO want builtin clang and llvm support.
-# When selected, pass LLVM_CONFIG=/path/to/llvm-config to `make' if
-# llvm-config is not in $PATH.
-#
 # Define CORESIGHT if you DO WANT support for CoreSight trace decoding.
 #
 # Define NO_AIO if you do not want support of Posix AIO based trace
@@ -425,19 +421,6 @@ endif
 EXTLIBS := $(call filter-out,$(EXCLUDE_EXTLIBS),$(EXTLIBS))
 LIBS = -Wl,--whole-archive $(PERFLIBS) $(EXTRA_PERFLIBS) -Wl,--no-whole-archive -Wl,--start-group $(EXTLIBS) -Wl,--end-group
 
-ifeq ($(USE_CLANG), 1)
-  LIBS += -L$(shell $(LLVM_CONFIG) --libdir) -lclang-cpp
-endif
-
-ifeq ($(USE_LLVM), 1)
-  LIBLLVM = $(shell $(LLVM_CONFIG) --libs all) $(shell $(LLVM_CONFIG) --system-libs)
-  LIBS += -L$(shell $(LLVM_CONFIG) --libdir) $(LIBLLVM)
-endif
-
-ifeq ($(USE_CXX), 1)
-  LIBS += -lstdc++
-endif
-
 export INSTALL SHELL_PATH
 
 ### Build rules

tools/build/feature/test-llvm-version.cpp

@@ -51,7 +51,6 @@ perf-y += sdt.o
 perf-y += is_printable_array.o
 perf-y += bitmap.o
 perf-y += perf-hooks.o
-perf-y += clang.o
 perf-y += unit_number__scnprintf.o
 perf-y += mem2node.o
 perf-y += maps.o

tools/build/feature/test-llvm.cpp

@@ -108,7 +108,6 @@ static struct test_suite *generic_tests[] = {
 	&suite__is_printable_array,
 	&suite__bitmap_print,
 	&suite__perf_hooks,
-	&suite__clang,
 	&suite__unit_number__scnprint,
 	&suite__mem2node,
 	&suite__time_utils,

tools/perf/Makefile.config

@@ -95,7 +95,6 @@ make_with_babeltrace:= LIBBABELTRACE=1
 make_with_coresight := CORESIGHT=1
 make_no_sdt	    := NO_SDT=1
 make_no_syscall_tbl := NO_SYSCALL_TABLE=1
-make_with_clangllvm := LIBCLANGLLVM=1
 make_no_libpfm4     := NO_LIBPFM4=1
 make_with_gtk2      := GTK2=1
 make_refcnt_check   := EXTRA_CFLAGS="-DREFCNT_CHECKING=1"