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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 25 Feb 2019 21:43:24 -0800
Message-ID: <CAKwvOd=PsmVmxoQVT1fhGx+eMkKRqJV_yUQ56_Fs0R-guTuo2Q@mail.gmail.com>
Subject: Re: [PATCH] powerpc/xmon: Fix opcode being uninitialized in print_insn_powerpc
To:     Nathan Chancellor <natechancellor@gmail.com>
Cc:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        linuxppc-dev@lists.ozlabs.org, LKML <linux-kernel@vger.kernel.org>,
        Joel Stanley <joel@jms.id.au>
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On Mon, Feb 25, 2019 at 9:39 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> When building with -Wsometimes-uninitialized, Clang warns:
>
> arch/powerpc/xmon/ppc-dis.c:157:7: warning: variable 'opcode' is used
> uninitialized whenever 'if' condition is false
> [-Wsometimes-uninitialized]
>   if (cpu_has_feature(CPU_FTRS_POWER9))
>       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> arch/powerpc/xmon/ppc-dis.c:167:7: note: uninitialized use occurs here
>   if (opcode == NULL)
>       ^~~~~~
> arch/powerpc/xmon/ppc-dis.c:157:3: note: remove the 'if' if its
> condition is always true
>   if (cpu_has_feature(CPU_FTRS_POWER9))
>   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> arch/powerpc/xmon/ppc-dis.c:132:38: note: initialize the variable
> 'opcode' to silence this warning
>   const struct powerpc_opcode *opcode;
>                                      ^
>                                       = NULL
> 1 warning generated.
>
> This warning seems to make no sense on the surface because opcode is set
> to NULL right below this statement. However, there is a comma instead of
> semicolon to end the dialect assignment, meaning that the opcode
> assignment only happens in the if statement. Properly terminate that
> line so that Clang no longer warns.
>
> Fixes: 5b102782c7f4 ("powerpc/xmon: Enable disassembly files (compilation changes)")
> Link: https://github.com/ClangBuiltLinux/linux/issues/390
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>

haha! (shows office mates).  Nice find, and fix!
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  arch/powerpc/xmon/ppc-dis.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/xmon/ppc-dis.c b/arch/powerpc/xmon/ppc-dis.c
> index 9deea5ee13f6..27f1e6415036 100644
> --- a/arch/powerpc/xmon/ppc-dis.c
> +++ b/arch/powerpc/xmon/ppc-dis.c
> @@ -158,7 +158,7 @@ int print_insn_powerpc (unsigned long insn, unsigned long memaddr)
>      dialect |= (PPC_OPCODE_POWER5 | PPC_OPCODE_POWER6 | PPC_OPCODE_POWER7
>                 | PPC_OPCODE_POWER8 | PPC_OPCODE_POWER9 | PPC_OPCODE_HTM
>                 | PPC_OPCODE_ALTIVEC | PPC_OPCODE_ALTIVEC2
> -               | PPC_OPCODE_VSX | PPC_OPCODE_VSX3),
> +               | PPC_OPCODE_VSX | PPC_OPCODE_VSX3);
>
>    /* Get the major opcode of the insn.  */
>    opcode = NULL;
> --
> 2.21.0
>


-- 
Thanks,
~Nick Desaulniers