Re: [RFC PATCH v6 25/32] perf tools: Add 'bpf.' config section to perf default config

Wangnan (F)
2015-06-10T00:55:16Z

On 2015/6/10 7:43, Alexei Starovoitov wrote:
> On 6/8/15 10:50 PM, Wang Nan wrote:
>> perf_bpf_config() is added to parse 'bpf' section in perf config file.
>> Following is an example:
>>
>> [bpf]
>> clang-path = /llvm/bin/x86_64-linux-clang"
>> llc-path = /llvm/bin/x86_64-linux-llc"
>> clang-opt = "-nostdinc -isystem /llvm/lib/clang/include
>> -I/kernel/arch/x86/include ..."
>> llc-opt = ""
>
> a section to specify -I flags to compile prog.c is useful,
> but users shouldn't be populating it manually for kernel headers.
> How about adding a script that can figure out $(LINUXINCLUDE)
> automatically ?
> You can even invoke such flag detector from perf via something like:
> f = open /tmpdir/Makefile
> fprintf(f, "obj-y := dummy.o\n");
> fprintf(f, "$(obj)/%%.o: $(src)/%%.c\n");
> fprintf(f, "\t@echo -n \"$(NOSTDINC_FLAGS) $(LINUXINCLUDE)
> $(EXTRA_CFLAGS)\" > %s\n", cachefile);
> snprintf(cmd, "make -s -C /lib/modules/%s/build M=%s dummy.o",
> uts_release, tmpdir);
> system(cmd);
> read flags from cachefile and cache it for the future.
> ...
> or as independent script that populates .perfconfig
>

That's cool, but could I implement it later? Introducing such stuffs
also introduces
a lot of trouble tasks:

1. Dependency on make and kernel build. We should search make and kbuild
dir dynamically
and also gives users the right to specify them by theirselves. A lot
of configuration
options should be appended: --make-path=/path/to/make
--kbuild-dir=kernel/build/dir
in cmdline and
[kbuild]
make_path = /path/to/make
kbuild_dir = /path/to/kbuild
in .perfconfig.

2. Selection of architectures. Although currently we want it to work
only when we dynamically
compile a script, I think finally we should consider cross compiling
bpf objects. Then cmdline
generation becomes complex. Also, --arch and [kbuild.arch] should
also be introduced.

3. Kernel dependency. Consider if kernel decides to change its interface...

I think currently we can pop some messages to let user know how to get
include dirs manually,
let further patches to do it for them automatically.

P.S.

Have you tested your Makefile? It doesn't work for me:

# cat ./Makefile
obj-y := dummy.o

$(obj)/%.o: $(src)/%.c
@echo -n "$(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(EXTRA_CFLAGS)" > xxxx

# make -s -C kernel/build/dir M=`pwd` dummy.o
make[2]: *** No rule to make target `dummy.o'. Stop.
make[1]: *** [sub-make] Error 2
make: *** [__sub-make] Error 2

Thank you.