RE: [PATCH V2 25/37] perf script: Add synthesized Intel PT power and ptwrite events

[Hunter, Adrian]

Sorry for the top-post...

Yeah, I've now mixed up the variable attribute:

	https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#Common-Variable-Attributes
 
with the type attribute:

	https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#Common-Type-Attributes

Late here, so maybe it will make more sense tomorrow.

-----Original Message-----
From: Arnaldo Carvalho de Melo [mailto:acme@xxxxxxxxxx] 
Sent: Wednesday, June 28, 2017 9:54 PM
To: Hunter, Adrian <adrian.hunter@xxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx
Subject: Re: [PATCH V2 25/37] perf script: Add synthesized Intel PT power and ptwrite events

Em Wed, Jun 28, 2017 at 08:40:25PM +0300, Adrian Hunter escreveu:
> On 06/28/2017 04:04 PM, Arnaldo Carvalho de Melo wrote:
> > Em Fri, May 26, 2017 at 11:17:26AM +0300, Adrian Hunter escreveu:
> >> Add definitions for synthesized Intel PT events for power and ptwrite.
> >  
> >> +++ b/tools/perf/util/event.h
> >> +/*
> >> + * Raw data formats for synthesized events. Note that raw data 
> >> +plus the raw data
> >> + * size (4 bytes) must align to 8-bytes.
> >> + */
> >> +
> >> +struct perf_synth_intel_ptwrite {
> >> +	union {
> >> +		struct {
> >> +			u32	ip		:  1,
> >> +				reserved	: 31;
> >> +		};
> >> +		u32	flags;
> >> +	};
> >> +	u64	payload;
> >> +} __packed;
> > 
> > 
> > some versions of clang and gcc dislike this __packed here:
> > 
> > In file included from builtin-script.c:5:
> > In file included from /git/linux/tools/perf/util/debug.h:8:
> > /git/linux/tools/perf/util/event.h:274:2: error: packed attribute is unnecessary for (null) [-Werror,-Wpacked]
> >         union {
> >         ^
> > /git/linux/tools/perf/util/event.h:285:6: error: packed attribute is unnecessary for 'reserved' [-Werror,-Wpacked]
> >         u32 reserved;
> >             ^
> > /git/linux/tools/perf/util/event.h:298:6: error: packed attribute is unnecessary for 'reserved' [-Werror,-Wpacked]
> >         u32 reserved;
> >             ^
> > /git/linux/tools/perf/util/event.h:322:6: error: packed attribute is unnecessary for 'reserved' [-Werror,-Wpacked]
> >         u32 reserved;
> >             ^
> > 4 errors generated.
> > mv: can't rename '/tmp/build/perf/.builtin-script.o.tmp': No such 
> > file or directory
> > 
> > /git/linux/tools/build/Makefile.build:101: recipe for target 
> > '/tmp/build/perf/builtin-script.o' failed
> > 
> > Failing in various distros:
> > 
> > [root@jouet ~]# waitp 3940 ; time dm
> >    1 92.3684147260 alpine:3.4: FAIL
> >    2 95.9136365930 alpine:3.5: FAIL
> >    3 104.8328303770 alpine:3.6: FAIL
> >    4 121.6584964930 alpine:edge: FAIL
> >    5 37.2536373490 android-ndk:r12b-arm: Ok
> >    6 83.9077612370 archlinux:latest: Ok
> >    7 14.7094639200 centos:5: FAIL
> >    8 16.6371634320 centos:6: FAIL
> > 
> > Investigating...
> 
> Re-reading the documentation for __packed, it seems like the following 
> might be better:

Humm, can you provide the URL for such docs? I always saw packed as an attribute for a struct, not for a member... For members "aligned" is what I'm used to see:

   __attribute__ ((aligned (8)))

In the kernel sources there are a few such cases as you suggest:

[acme@jouet linux]$ find include/ -name "*.h"| xargs grep -w __packed | grep -v } | grep -v "struct __packed" | wc -l
12
[acme@jouet linux]$

But most are the other way, i.e. tagging the packed attribute to the whole struct, as you originally did :-\

- Arnaldo
 
> diff --git a/tools/perf/util/event.h b/tools/perf/util/event.h index 
> c283603f59c7..a7547cb3b760 100644
> --- a/tools/perf/util/event.h
> +++ b/tools/perf/util/event.h
> @@ -278,8 +278,8 @@ struct perf_synth_intel_ptwrite {
>  		};
>  		u32	flags;
>  	};
> -	u64	payload;
> -} __packed;
> +	u64	payload __packed;
> +};
>  
>  struct perf_synth_intel_mwait {
>  	u32 reserved;
> @@ -291,8 +291,8 @@ struct perf_synth_intel_mwait {
>  				reserved2	: 30;
>  		};
>  		u64	payload;
> -	};
> -} __packed;
> +	} __packed;
> +};
>  
>  struct perf_synth_intel_pwre {
>  	u32 reserved;
> @@ -305,8 +305,8 @@ struct perf_synth_intel_pwre {
>  				reserved2	: 48;
>  		};
>  		u64	payload;
> -	};
> -} __packed;
> +	} __packed;
> +};
>  
>  struct perf_synth_intel_exstop {
>  	union {
> @@ -328,8 +328,8 @@ struct perf_synth_intel_pwrx {
>  				reserved1	: 52;
>  		};
>  		u64	payload;
> -	};
> -} __packed;
> +	} __packed;
> +};
>  
>  struct perf_synth_intel_cbr {
>  	union {