Re: [PATCH 2/3] perf disasm: Define stubs for the LLVM and capstone disassemblers

[Ian Rogers]

On Mon, Nov 11, 2024 at 7:18 AM Arnaldo Carvalho de Melo
<acme@xxxxxxxxxx> wrote:
>
> From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
>
> This reduces the number of ifdefs in the main symbol__disassemble()
> method and paves the way for allowing the user to configure the
> disassemblers of preference.
>
> Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Cc: Athira Rajeev <atrajeev@xxxxxxxxxxxxxxxxxx>
> Cc: Ian Rogers <irogers@xxxxxxxxxx>
> Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> Cc: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> Cc: Steinar H. Gunderson <sesse@xxxxxxxxxx>
> Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

Acked-by: Ian Rogers <irogers@xxxxxxxxxx>
Style nit below.

> ---
>  tools/perf/util/disasm.c | 40 ++++++++++++++++++++++++++++++++--------
>  1 file changed, 32 insertions(+), 8 deletions(-)
>
> diff --git a/tools/perf/util/disasm.c b/tools/perf/util/disasm.c
> index 36cf61602c17fe69..83df1da20a7b16cd 100644
> --- a/tools/perf/util/disasm.c
> +++ b/tools/perf/util/disasm.c
> @@ -1422,6 +1422,13 @@ read_symbol(const char *filename, struct map *map, struct symbol *sym,
>         free(buf);
>         return NULL;
>  }
> +#else // defined(HAVE_LIBCAPSTONE_SUPPORT) || defined(HAVE_LIBLLVM_SUPPORT)
> +static void symbol__disassembler_missing(const char *disassembler, const char *filename,
> +                                        struct symbol *sym)
> +{
> +       pr_debug("The %s disassembler isn't linked in for %s in %s\n",
> +                disassembler, sym->name, filename);
> +}

I can see why you're doing this but it seems overkill to have a
function just for the sake of 1 pr_debug. The #ifdefs make this look
like it could be doing more. Perhaps the style:
```
static int symbol__disassemble_capstone(char *filename, struct symbol
*sym, struct annotate_args *args)
{
#ifndef HAVE_LIBCAPSTONE_SUPPORT
    pr_debug("The capstone disassembler isn't linked in for %s in
%s\n", sym->name, filename);
    return -1;
#else
    ...
#endif
}
```
Would be preferable as the #ifdef's scope is more limited, you don't
need to hunt around for 1 of 3 functions, etc.

Thanks,
Ian

>  #endif
>
>  #ifdef HAVE_LIBCAPSTONE_SUPPORT
> @@ -1715,7 +1722,20 @@ static int symbol__disassemble_capstone(char *filename, struct symbol *sym,
>         count = -1;
>         goto out;
>  }
> -#endif
> +#else // HAVE_LIBCAPSTONE_SUPPORT
> +static int symbol__disassemble_capstone(char *filename, struct symbol *sym,
> +                                       struct annotate_args *args)
> +       symbol__disassembler_missing("capstone", filename, sym);
> +       return -1;
> +}
> +
> +static int symbol__disassemble_capstone_powerpc(char *filename, struct symbol *sym,
> +                                               struct annotate_args *args __maybe_unused)
> +{
> +       symbol__disassembler_missing("capstone powerpc", filename, sym);
> +       return -1;
> +}
> +#endif // HAVE_LIBCAPSTONE_SUPPORT
>
>  static int symbol__disassemble_raw(char *filename, struct symbol *sym,
>                                         struct annotate_args *args)
> @@ -1983,7 +2003,14 @@ static int symbol__disassemble_llvm(char *filename, struct symbol *sym,
>         free(line_storage);
>         return ret;
>  }
> -#endif
> +#else // HAVE_LIBLLVM_SUPPORT
> +static int symbol__disassemble_llvm(char *filename, struct symbol *sym,
> +                                   struct annotate_args *args __maybe_unused)
> +{
> +       symbol__disassembler_missing("LLVM", filename, sym);
> +       return -1;
> +}
> +#endif // HAVE_LIBLLVM_SUPPORT
>
>  /*
>   * Possibly create a new version of line with tabs expanded. Returns the
> @@ -2242,24 +2269,21 @@ int symbol__disassemble(struct symbol *sym, struct annotate_args *args)
>                         err = symbol__disassemble_raw(symfs_filename, sym, args);
>                         if (err == 0)
>                                 goto out_remove_tmp;
> -#ifdef HAVE_LIBCAPSTONE_SUPPORT
> +
>                         err = symbol__disassemble_capstone_powerpc(symfs_filename, sym, args);
>                         if (err == 0)
>                                 goto out_remove_tmp;
> -#endif
>                 }
>         }
>
> -#ifdef HAVE_LIBLLVM_SUPPORT
>         err = symbol__disassemble_llvm(symfs_filename, sym, args);
>         if (err == 0)
>                 goto out_remove_tmp;
> -#endif
> -#ifdef HAVE_LIBCAPSTONE_SUPPORT
> +
>         err = symbol__disassemble_capstone(symfs_filename, sym, args);
>         if (err == 0)
>                 goto out_remove_tmp;
> -#endif
> +
>         err = symbol__disassemble_objdump(symfs_filename, sym, args);
>
>  out_remove_tmp:
> --
> 2.47.0
>