linux-kernel - Re: [PATCH] objtool: drop redundant flags generation

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Message-Id: <20170307091645.88a9c9511361a39dc5dad191@kernel.org>
Date:   Tue, 7 Mar 2017 09:16:45 +0100
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Nicholas Mc Guire <der.herr@...r.at>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] objtool: drop redundant flags generation

On Mon,  6 Mar 2017 18:00:25 +0100
Nicholas Mc Guire <der.herr@...r.at> wrote:

> The generator was emitting quite a few duplicate flags which was making
> doublebitand.cocci nervous. This awk hack resolves the duplicate issue.

Yes, I know that.
I don't think that the duplicating those flags in "automatic generated"
source code is not so harmful. I personally prefer to keep awk code
simpler...

Thanks,

> 
> Signed-off-by: Nicholas Mc Guire <der.herr@...r.at>
> ---
> 
> The coccinelle complaints emitted was about 230 findings total:
> ./arch/x86/lib/inat-tables.c:214:10-20: duplicated argument to & or |
> ./arch/x86/lib/inat-tables.c:214:23-33: duplicated argument to & or |
> ./arch/x86/lib/inat-tables.c:218:10-20: duplicated argument to & or |
> ./arch/x86/lib/inat-tables.c:218:23-33: duplicated argument to & or |
> ....
> ./tools/objtool/arch/x86/insn/inat-tables.c:214:10-20: duplicated argument to & or |
> ./tools/objtool/arch/x86/insn/inat-tables.c:214:23-33: duplicated argument to & or |
> ./tools/objtool/arch/x86/insn/inat-tables.c:218:10-20: duplicated argument to & or |
> ./tools/objtool/arch/x86/insn/inat-tables.c:218:23-33: duplicated argument to & or |
> ...
> spatch --sp-file scripts/coccinelle/tests/doublebitand.cocci inat-tables.c -D report
> will give you the full list - all are caused by duplicates in the generated
> output by the add_flags function in the two instances of gen-insn-attr-x86.awk.
> 
> Q: The two copies of gen-insn-attr-x86.awk are identical and its not actually clear
>    why this duplication is needed ? Further the maintainers list emitted for the
>    two files differ.
> 
> Patch was checked by manual review of the diff between the initial file and the
> regenerated file after the below patch was applied.
> Second verification was by make tools/objtool and comparing the generated binaries
> in tools/objtool/arch/x86/decode.o with diff.
> 
> Patch is against 4.11-rc1 (localversion-next is next-20170306)
> 
>  arch/x86/tools/gen-insn-attr-x86.awk              | 12 ++++++++++--
>  tools/objtool/arch/x86/insn/gen-insn-attr-x86.awk | 12 ++++++++++--
>  2 files changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/tools/gen-insn-attr-x86.awk b/arch/x86/tools/gen-insn-attr-x86.awk
> index a3d2c62..9cdeefe 100644
> --- a/arch/x86/tools/gen-insn-attr-x86.awk
> +++ b/arch/x86/tools/gen-insn-attr-x86.awk
> @@ -226,8 +226,16 @@ function print_table(tbl,name,fmt,n)
>  }
>  
>  function add_flags(old,new) {
> -	if (old && new)
> -		return old " | " new
> +	if (old == new)
> +		return old
> +	if (old && new) {
> +		if(match(old,new))
> +			return old
> +		else if(match(new,old))
> +			return new
> +		else
> +			return old " | " new
> +        }
>  	else if (old)
>  		return old
>  	else
> diff --git a/tools/objtool/arch/x86/insn/gen-insn-attr-x86.awk b/tools/objtool/arch/x86/insn/gen-insn-attr-x86.awk
> index a3d2c62..9cdeefe 100644
> --- a/tools/objtool/arch/x86/insn/gen-insn-attr-x86.awk
> +++ b/tools/objtool/arch/x86/insn/gen-insn-attr-x86.awk
> @@ -226,8 +226,16 @@ function print_table(tbl,name,fmt,n)
>  }
>  
>  function add_flags(old,new) {
> -	if (old && new)
> -		return old " | " new
> +	if (old == new)
> +		return old
> +	if (old && new) {
> +		if(match(old,new))
> +			return old
> +		else if(match(new,old))
> +			return new
> +		else
> +			return old " | " new
> +        }
>  	else if (old)
>  		return old
>  	else
> -- 
> 2.1.4
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>