linux-kernel - Re: [PATCH] perf unwind: Limit warnings when asked for not supported unwind

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Date:   Fri, 16 Jun 2017 13:25:04 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     He Kuang <hekuang@...wei.com>, lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Namhyung Kim <namhyung@...nel.org>,
        David Ahern <dsahern@...il.com>
Subject: Re: [PATCH] perf unwind: Limit warnings when asked for not supported
 unwind

Em Fri, Jun 16, 2017 at 02:12:53PM +0200, Jiri Olsa escreveu:
> Ingo reported following warning flooding the report out:
> 
>   unwind: target platform=x86 is not supported
> 
> We trigger this warning when the dwarf unwinder is asked to
> process architecture which wasn't compiled in, like when you
> get 32bit application samples on your 64bit server and you
> don't have the 32bit remote unwind support compiled in.
> 
> This patch limits the warning to single message for arch,
> and adds bits info. Above message is changed to:
> 
>   unwind: target platform=x86 32bit is not supported

Can we have a more informative message telling the user what is
necessary to have this feature supported?

The way you phrased it looks like it is not supported at all, while what
I read in the discussion is that one needs to have specific versions of
support libraries installed to have this working, right?

- Arnaldo
 
> Cc: He Kuang <hekuang@...wei.com>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  tools/perf/util/unwind-libunwind.c | 29 ++++++++++++++++++++++++-----
>  1 file changed, 24 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/perf/util/unwind-libunwind.c b/tools/perf/util/unwind-libunwind.c
> index 6d542a4e0648..1439a6bcfa07 100644
> --- a/tools/perf/util/unwind-libunwind.c
> +++ b/tools/perf/util/unwind-libunwind.c
> @@ -1,12 +1,24 @@
> +#include <linux/err.h>
>  #include "unwind.h"
>  #include "thread.h"
>  #include "session.h"
>  #include "debug.h"
>  #include "arch/common.h"
>  
> -struct unwind_libunwind_ops __weak *local_unwind_libunwind_ops;
> -struct unwind_libunwind_ops __weak *x86_32_unwind_libunwind_ops;
> -struct unwind_libunwind_ops __weak *arm64_unwind_libunwind_ops;
> +enum {
> +	ERR_LOCAL  = 0,
> +	ERR_X86_32 = 1,
> +	ERR_ARM64  = 2,
> +};
> +
> +/*
> + * Set default error values, so we can warn appropriately when
> + * the support is not compiled in. Using negative values so we
> + * can use ERR macros.
> + */
> +struct unwind_libunwind_ops __weak *local_unwind_libunwind_ops  = (void *) -ERR_LOCAL;
> +struct unwind_libunwind_ops __weak *x86_32_unwind_libunwind_ops = (void *) -ERR_X86_32;
> +struct unwind_libunwind_ops __weak *arm64_unwind_libunwind_ops  = (void *) -ERR_ARM64;
>  
>  static void unwind__register_ops(struct thread *thread,
>  			  struct unwind_libunwind_ops *ops)
> @@ -48,8 +60,15 @@ int unwind__prepare_access(struct thread *thread, struct map *map,
>  			ops = arm64_unwind_libunwind_ops;
>  	}
>  
> -	if (!ops) {
> -		pr_err("unwind: target platform=%s is not supported\n", arch);
> +	if (IS_ERR(ops)) {
> +		static unsigned long warned;
> +		long bit = -PTR_ERR(ops);
> +
> +		if (!test_and_set_bit(bit, &warned)) {
> +			pr_err("unwind: target platform=%s %dbit is not supported\n",
> +				arch, dso_type == DSO__TYPE_64BIT ? 64 : 32);
> +		}
> +
>  		return -1;
>  	}
>  out_register:
> -- 
> 2.9.4