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Re: [PATCH 1/4] tools/tests/x86_emulator: fix 'shifting a negative signed value is undefined'
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Edwin Torok <edwin.torok@xxxxxxxxxx>
- Date: Tue, 24 Feb 2026 10:12:27 +0000
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 24 Feb 2026 10:12:40 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHcpKvhICvggy+CX02UgLA2L8U/0bWQbKoAgAE2GYA=
- Thread-topic: [PATCH 1/4] tools/tests/x86_emulator: fix 'shifting a negative signed value is undefined'
> On 23 Feb 2026, at 15:42, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>
> On 23.02.2026 11:04, Edwin Török wrote:
>> --- a/tools/tests/x86_emulator/test_x86_emulator.c
>> +++ b/tools/tests/x86_emulator/test_x86_emulator.c
>> @@ -1161,7 +1161,7 @@ int main(int argc, char **argv)
>> instr[0] = 0x4d; instr[1] = 0x0f; instr[2] = 0xbb; instr[3] = 0x03;
>> regs.eflags = EFLAGS_ALWAYS_SET;
>> regs.rip = (unsigned long)&instr[0];
>> - regs.r8 = (-1L << 40) + 1;
>> + regs.r8 = (~0ULL << 40) + 1;
>
> While -1 vs ~0 doesn't make a big difference, I think we want to stick to
> "register size" here, and hence have only UL as the suffix. Then (happy to
> adjust while committing):
> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
>
That is what I tried initially, but I got an error that the shift exceeds the
width of the type in (0UL << 40).
(I think the failure was with -m32 in the CI, but can’t find it now)
Best regards,
—Edwin
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