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

Arnaldo Carvalho de Melo
2017-06-28T20:26:43Z

Em Wed, Jun 28, 2017 at 08:21:37PM +0000, Hunter, Adrian escreveu:
> 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.

Right, and I've not been able to focus on this, but I think the problem
is with packed mixed with unnamed unions :-\

- Arnaldo

> -----Original Message-----
> From: Arnaldo Carvalho de Melo [mailto:acme@kernel.org]
> Sent: Wednesday, June 28, 2017 9:54 PM
> To: Hunter, Adrian <adrian.hunter@intel.com>
> Cc: Andi Kleen <ak@linux.intel.com>; linux-kernel@vger.kernel.org
> 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 {