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

[Arnaldo Carvalho de Melo <acme@redhat.com>]

Em Sat, Aug 29, 2015 at 04:21:56AM +0000, Wang Nan escreveu:
> 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_GET_REG_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.
> 
> Signed-off-by: Wang Nan <wangnan0@huawei.com>
> Cc: Alexei Starovoitov <ast@plumgrid.com>
> Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: David Ahern <dsahern@gmail.com>
> Cc: He Kuang <hekuang@huawei.com>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: Kaixu Xia <xiakaixu@huawei.com>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Zefan Li <lizefan@huawei.com>
> Cc: pi3orama@163.com
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Link: http://lkml.kernel.org/n/1436445342-1402-33-git-send-email-wangnan0@huawei.com
> ---
>  tools/perf/config/Makefile           | 12 ++++++++++++
>  tools/perf/util/include/dwarf-regs.h |  7 +++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/tools/perf/config/Makefile b/tools/perf/config/Makefile
> index 38a4144..d46765b7 100644
> --- a/tools/perf/config/Makefile
> +++ b/tools/perf/config/Makefile
> @@ -314,6 +314,18 @@ ifndef NO_LIBELF
>        CFLAGS += -DHAVE_LIBBPF_SUPPORT
>        $(call detected,CONFIG_LIBBPF)
>      endif
> +
> +    ifndef NO_DWARF
> +      ifneq ($(origin PERF_HAVE_ARCH_GET_REG_INFO), undefined)
> +        CFLAGS += -DHAVE_BPF_PROLOGUE
> +        $(call detected,CONFIG_BPF_PROLOGUE)
> +      else
> +        msg := $(warning BPF prologue is not supported by architecture $(ARCH));

Shouldn't this be replace to something like:

        msg := $(warning BPF prologue is not supported by architecture $(ARCH), missing ARCH_GET_REG_INFO);

Or even in lowercase?

> +      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..3dda083 100644
> --- a/tools/perf/util/include/dwarf-regs.h
> +++ b/tools/perf/util/include/dwarf-regs.h
> @@ -5,4 +5,11 @@
>  const char *get_arch_regstr(unsigned int n);
>  #endif

Shouldn't this test against PERF_HAVE_ARCH_GET_REG_INFO instead? I.e.
is arch_get_reg_info() only allowed to work with eBPF? I guess not,
right?
  
> +#ifdef HAVE_BPF_PROLOGUE
> +/*
> + * Arch should support fetching the offset of a register in pt_regs
> + * by its name.
> + */
> +int arch_get_reg_info(const char *name, int *offset);
> +#endif
>  #endif
> -- 
> 2.1.0