Re: [PATCH v2 4/4] perf augmented_raw_syscalls: Document clang configuration

[Leo Yan]

On Thu, Jun 06, 2019 at 11:08:00AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Thu, Jun 06, 2019 at 05:48:45PM +0800, Leo Yan escreveu:
> > To build this program successfully with clang, there have three
> > compiler options need to be specified:
> > 
> >   - Header file path: tools/perf/include/bpf;
> >   - Specify architecture;
> >   - Define macro __NR_CPUS__.
> 
> So, this shouldn't be needed, all of this is supposed to be done
> automagically, have you done a 'make -C tools/perf install'?

I missed the up operation.  But after git pulled the lastest code base
from perf/core branch and used the command 'make -C tools/perf
install', I still saw the eBPF build failure.

Just now this issue is fixed after I removed the config
'clang-bpf-cmd-template' from ~/.perfconfig;  the reason is I followed
up the Documentation/perf-config.txt to set the config as below:

  clang-bpf-cmd-template = "$CLANG_EXEC -D__KERNEL__ $CLANG_OPTIONS \
                          $KERNEL_INC_OPTIONS -Wno-unused-value \
                          -Wno-pointer-sign -working-directory \
                          $WORKING_DIR -c $CLANG_SOURCE -target bpf \
                          -O2 -o -"

In fact, util/llvm-utils.c has updated the default configuration as
below:

  #define CLANG_BPF_CMD_DEFAULT_TEMPLATE                          \
                "$CLANG_EXEC -D__KERNEL__ -D__NR_CPUS__=$NR_CPUS "\
                "-DLINUX_VERSION_CODE=$LINUX_VERSION_CODE "     \
                "$CLANG_OPTIONS $PERF_BPF_INC_OPTIONS $KERNEL_INC_OPTIONS " \
                "-Wno-unused-value -Wno-pointer-sign "          \
                "-working-directory $WORKING_DIR "              \
                "-c \"$CLANG_SOURCE\" -target bpf $CLANG_EMIT_LLVM -O2 -o - $LLVM_OPTIONS_PIPE"

Maybe should update Documentation/perf-config.txt to tell users the
real default value of clang-bpf-cmd-template?

Thanks,
Leo Yan