Re: [Xen-devel] [PATCH v4 4/4] build: enable no-parentheses in clang

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 14/02/17 14:06, Roger Pau Monne wrote:
> On Tue, Feb 14, 2017 at 06:56:12AM -0700, Jan Beulich wrote:
>>>>> On 14.02.17 at 13:30, <roger.pau@xxxxxxxxxx> wrote:
>>> --- a/Config.mk
>>> +++ b/Config.mk
>>> @@ -212,9 +212,6 @@ CFLAGS += -std=gnu99
>>>  
>>>  CFLAGS += -Wall -Wstrict-prototypes
>>>  
>>> -# Clang complains about macros that expand to 'if ( ( foo == bar ) ) ...'
>>> -CFLAGS-$(clang) += -Wno-parentheses
>> Taking the comment being removed here together with ....
>>
>>> --- a/xen/arch/x86/traps.c
>>> +++ b/xen/arch/x86/traps.c
>>> @@ -2011,7 +2011,7 @@ uint32_t guest_io_read(unsigned int port, unsigned 
>>> int bytes,
>>>          {
>>>              sub_data = pv_pit_handler(port, 0, 0);
>>>          }
>>> -        else if ( (port == RTC_PORT(0)) )
>>> +        else if ( port == RTC_PORT(0) )
>>>          {
>>>              sub_data = currd->arch.cmos_idx;
>>>          }
>>> @@ -2080,7 +2080,7 @@ void guest_io_write(unsigned int port, unsigned int 
>>> bytes, uint32_t data,
>>>          {
>>>              pv_pit_handler(port, (uint8_t)data, 1);
>>>          }
>>> -        else if ( (port == RTC_PORT(0)) )
>>> +        else if ( port == RTC_PORT(0) )
>>>          {
>>>              currd->arch.cmos_idx = data;
>>>          }
>> ... the code adjustments all being to other than macros I wonder
>> whether in the version you use the issue is no longer being
>> reported in macro expansions, but older clang still chokes on such.
>> Or did you go check that we have no such uses left (which seems
>> unlikely to me)?
> I assume that in recent versions of clang this is no longer an issue. Travis
> tests with clang 3.5 and I test with 3.8, and none of them find any issues.
> IMHO we should turn it on because I barely doubt anyone is building Xen with
> older versions of clang, when I started working on this the clang support was
> completely bitrotted.

There was some Clang 3.2 support in the past, but it had completely
bitrotten.

Clang 3.5 is our documented minimum, so I think it is reasonable to take
these clobbers out, seeing as they are not needed.

~Andrew

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