linux-kernel - Re: [SIL2review] [PATCH] objtool: Use value of intended enum to compile with clang

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Message-ID: <20171210201903.GA13846@osadl.at>
Date:   Sun, 10 Dec 2017 20:19:03 +0000
From:   Nicholas Mc Guire <der.herr@...r.at>
To:     Lukas Bulwahn <lukas.bulwahn@...il.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, sil2review@...ts.osadl.org,
        Jiri Slaby <jslaby@...e.cz>, Ingo Molnar <mingo@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [SIL2review] [PATCH] objtool: Use value of intended enum to
 compile with clang

On Sun, Dec 10, 2017 at 07:35:00PM +0100, Lukas Bulwahn wrote:
> Just use the right value and avoid an implicit conversion between the two
> enumeration types that just happened to work in this case. It seems that
> this must have just been overlooked in the new implementation of objtool
> in commit baa41469a7b9 ("objtool: Implement stack validation 2.0").
> 
> I found this when compiling the kernel with clang-5.0, i.e., executing
> 
>   make HOSTCC=clang-5.0 CC=clang-5.0 defconfig && \
>   make HOSTCC=clang-5.0 CC=clang-5.0
> 
> fails with:
> 
> ```
> arch/x86/decode.c:141:20: error: implicit conversion from enumeration type 'enum op_src_type' to different enumeration type 'enum op_dest_type' [-Werror,-Wenum-conversion]
>                         op->dest.type = OP_SRC_REG;
>                                       ~ ^~~~~~~~~~
> 1 error generated.
> ```

given the declaration in tools/objtool/arch.h
enum op_dest_type {
        OP_DEST_REG,
        ...

enum op_src_type {
        OP_SRC_REG,
        ...

the change seems correct and it is clear why it worked with the wrong type

> 
> Fixes: baa41469a7b9 ("objtool: Implement stack validation 2.0")
> Signed-off-by: Lukas Bulwahn <lukas.bulwahn@...il.com>
Reviewed-by: Nicholas Mc Guire <der.herr@...r.at>

> ---
>  tools/objtool/arch/x86/decode.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
> index 8acfc47..540a209 100644
> --- a/tools/objtool/arch/x86/decode.c
> +++ b/tools/objtool/arch/x86/decode.c
> @@ -138,7 +138,7 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
>  			*type = INSN_STACK;
>  			op->src.type = OP_SRC_ADD;
>  			op->src.reg = op_to_cfi_reg[modrm_reg][rex_r];
> -			op->dest.type = OP_SRC_REG;
> +			op->dest.type = OP_DEST_REG;
>  			op->dest.reg = CFI_SP;
>  		}
>  		break;
> -- 
> 2.7.4
> 
> _______________________________________________
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> SIL2review@...ts.osadl.org
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