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Date: Fri, 3 Mar 2017 17:06:01 +0100
From: "Edgar E. Iglesias" <edgar.iglesias@gmail.com>
Message-ID: <20170303160601.GA9606@toto>
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Subject: Re: [Qemu-devel] [PATCH for-2.9 4/6] disas/microblaze: Avoid
 unintended sign extension
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: QEMU Developers <qemu-devel@nongnu.org>, "patches@linaro.org" <patches@linaro.org>, Richard Henderson <rth@twiddle.net>, Paolo Bonzini <pbonzini@redhat.com>, Eduardo Habkost <ehabkost@redhat.com>, Laurent Vivier <laurent@vivier.eu>

On Fri, Mar 03, 2017 at 04:02:07PM +0000, Peter Maydell wrote:
> On 3 March 2017 at 15:58, Edgar E. Iglesias <edgar.iglesias@gmail.com> wrote:
> > On Fri, Mar 03, 2017 at 03:50:31PM +0000, Peter Maydell wrote:
> >> In read_insn_microblaze() we assemble 4 bytes into an 'unsigned
> >> long'.  If 'unsigned long' is 64 bits and the high byte has its top
> >> bit set, then C's implicit conversion from 'unsigned char' to 'int'
> >> for the shift will result in an unintended sign extension which sets
> >> the top 32 bits in 'inst'.  Add casts to prevent this.  (Spotted by
> >> Coverity, CID 1005401.)
> >
> > I'm OK with this but perhaps it would have been more readable to
> > change inst to uint32_t ? (All microblaze insns are 32bit).
> 
> I thought about that, but it was more invasive a change than
> I was happy with: you'd want to change not just 'inst' but
> also the return type of read_insn_microblaze, the opcode_mask
> field of struct op_code_struct, 'inst' and 'prev_inst' in
> print_insn_microblaze, the type of the instr arguments to
> get_field, get_field_imm, etc...

Ah, I see, didn't think about that...

Cheers,
Edgar