linux-kernel - Re: [PATCH 22/31] perf tools: Add BPF_PROLOGUE config options for further patches

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Date:	Wed, 2 Sep 2015 23:08:46 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	acme@...nel.org, linux-kernel@...r.kernel.org,
	Alexei Starovoitov <ast@...mgrid.com>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	David Ahern <dsahern@...il.com>, He Kuang <hekuang@...wei.com>,
	Jiri Olsa <jolsa@...nel.org>, Kaixu Xia <xiakaixu@...wei.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Zefan Li <lizefan@...wei.com>, pi3orama@....com,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH 22/31] perf tools: Add BPF_PROLOGUE config options for
 further patches

On Tue, Sep 01, 2015 at 06:59:48AM +0000, Wang Nan wrote:
> If both LIBBPF and DWARF are detected, it is possible to create prologue
> for eBPF programs to help them accessing kernel data. HAVE_BPF_PROLOGUE
> and CONFIG_BPF_PROLOGUE is added as flags for this feature.
> 
> PERF_HAVE_ARCH_REGS_QUERY_REGISTER_OFFSET indicates an architecture
> supports converting name of a register to its offset in
> 'struct pt_regs'. Without this support, BPF_PROLOGUE should be turned off.
> 
> HAVE_ARCH_REGS_QUERY_REGISTER_OFFSET is introduced as the corresponding
> CFLAGS of PERF_HAVE_ARCH_REGS_QUERY_REGISTER_OFFSET.
> 
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> Cc: Alexei Starovoitov <ast@...mgrid.com>
> Cc: Brendan Gregg <brendan.d.gregg@...il.com>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: David Ahern <dsahern@...il.com>
> Cc: He Kuang <hekuang@...wei.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Kaixu Xia <xiakaixu@...wei.com>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Zefan Li <lizefan@...wei.com>
> Cc: pi3orama@....com
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Link: http://lkml.kernel.org/n/1436445342-1402-33-git-send-email-wangnan0@huawei.com
> [wawngnan:
>  - Introduce new CFLAGS to control BPF prologue and arch_get_reg_info()
>    separately.
>  - Rename ARCH_GET_REG_INFO to ARCH_REGS_QUERY_REGISTER_OFFSET,
>    arch_get_reg_info() to regs_query_register_offset(), change its API accordingly
>    to make it similar to kernel's regs_query_register_offset().
> ]
> ---
>  tools/perf/config/Makefile           | 17 +++++++++++++++++
>  tools/perf/util/include/dwarf-regs.h |  8 ++++++++
>  2 files changed, 25 insertions(+)
> 
> diff --git a/tools/perf/config/Makefile b/tools/perf/config/Makefile
> index 38a4144..33785a1 100644
> --- a/tools/perf/config/Makefile
> +++ b/tools/perf/config/Makefile
> @@ -110,6 +110,11 @@ FEATURE_CHECK_CFLAGS-bpf = -I. -I$(srctree)/tools/include -I$(srctree)/arch/$(AR
>  # include ARCH specific config
>  -include $(src-perf)/arch/$(ARCH)/Makefile
>  
> +ifneq ($(origin PERF_HAVE_ARCH_REGS_QUERY_REGISTER_OFFSET), undefined)

Why not just using

  ifdef PERF_HAVE_ARCH_REGS_QUERY_REGISTER_OFFSET

?


> +  CFLAGS += -DHAVE_ARCH_REGS_QUERY_REGISTER_OFFSET
> +endif
> +
> +
>  include $(src-perf)/config/utilities.mak
>  
>  ifeq ($(call get-executable,$(FLEX)),)
> @@ -314,6 +319,18 @@ ifndef NO_LIBELF
>        CFLAGS += -DHAVE_LIBBPF_SUPPORT
>        $(call detected,CONFIG_LIBBPF)
>      endif
> +
> +    ifndef NO_DWARF
> +      ifneq ($(origin PERF_HAVE_ARCH_REGS_QUERY_REGISTER_OFFSET), undefined)

Ditto.

Thanks,
Namhyung


> +        CFLAGS += -DHAVE_BPF_PROLOGUE
> +        $(call detected,CONFIG_BPF_PROLOGUE)
> +      else
> +        msg := $(warning BPF prologue is not supported by architecture $(ARCH), missing regs_query_register_offset());
> +      endif
> +    else
> +      msg := $(warning DWARF support is off, BPF prologue is disabled);
> +    endif
> +
>    endif # NO_LIBBPF
>  endif # NO_LIBELF
>  
> diff --git a/tools/perf/util/include/dwarf-regs.h b/tools/perf/util/include/dwarf-regs.h
> index 8f14965..07c644e 100644
> --- a/tools/perf/util/include/dwarf-regs.h
> +++ b/tools/perf/util/include/dwarf-regs.h
> @@ -5,4 +5,12 @@
>  const char *get_arch_regstr(unsigned int n);
>  #endif
>  
> +#ifdef HAVE_ARCH_REGS_QUERY_REGISTER_OFFSET
> +/*
> + * Arch should support fetching the offset of a register in pt_regs
> + * by its name. See kernel's regs_query_register_offset in
> + * arch/xxx/kernel/ptrace.c.
> + */
> +int regs_query_register_offset(const char *name);
> +#endif
>  #endif
> -- 
> 1.8.3.4
> 
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