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Date:   Tue, 15 Dec 2020 22:49:59 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>
Subject: Re: [PATCH v2] perf callchain: Return directly when use '--call-graph
 dwarf' under !HAVE_DWARF_SUPPORT

Hello,

On Tue, Dec 15, 2020 at 10:35 AM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
>
> DWARF register mappings have not been defined for some architectures,
> at least for mips, so we can print an error message and then return
> directly when use '--call-graph dwarf'.
>
> E.g. without this patch:
>
> [root@...ux perf]# ./perf record --call-graph dwarf cd
> Error:
> The sys_perf_event_open() syscall returned with 89 (Function not implemented) for event (cycles).
> /bin/dmesg | grep -i perf may provide additional information.
>
> With this patch:
>
> [root@...ux perf]# ./perf record --call-graph dwarf cd
> DWARF is not supported for architecture mips64
>
>  Usage: perf record [<options>] [<command>]
>     or: perf record [<options>] -- <command> [<options>]
>
>         --call-graph <record_mode[,record_size]>
>                           setup and enables call-graph (stack chain/backtrace):
>
>                                 record_mode:    call graph recording mode (fp|dwarf|lbr)
>                                 record_size:    if record_mode is 'dwarf', max size of stack recording (<bytes>)
>                                                 default: 8192 (bytes)
>
>                                 Default: fp
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
>
> v2: Use HAVE_DWARF_SUPPORT to check

I'm not sure whether this is because of lack of dwarf library or kernel support.
Based on the error message, I guess it's from the kernel.  Then I think this
patch won't be sufficient..

Thanks,
Namhyung


>
>  tools/perf/util/callchain.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
> index 1b60985..ad08554 100644
> --- a/tools/perf/util/callchain.c
> +++ b/tools/perf/util/callchain.c
> @@ -18,6 +18,7 @@
>  #include <math.h>
>  #include <linux/string.h>
>  #include <linux/zalloc.h>
> +#include <sys/utsname.h>
>
>  #include "asm/bug.h"
>
> @@ -276,6 +277,7 @@ int parse_callchain_record(const char *arg, struct callchain_param *param)
>
>                 /* Dwarf style */
>                 } else if (!strncmp(name, "dwarf", sizeof("dwarf"))) {
> +#ifdef HAVE_DWARF_SUPPORT
>                         const unsigned long default_stack_dump_size = 8192;
>
>                         ret = 0;
> @@ -290,6 +292,15 @@ int parse_callchain_record(const char *arg, struct callchain_param *param)
>                                 ret = get_stack_size(tok, &size);
>                                 param->dump_size = size;
>                         }
> +#else
> +                       struct utsname uts;
> +
> +                       ret = uname(&uts);
> +                       pr_err("DWARF is not supported for architecture %s\n",
> +                               ret ? "unknown" : uts.machine);
> +
> +                       return -ENOTSUP;
> +#endif
>                 } else if (!strncmp(name, "lbr", sizeof("lbr"))) {
>                         if (!strtok_r(NULL, ",", &saveptr)) {
>                                 param->record_mode = CALLCHAIN_LBR;
> --
> 2.1.0
>

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