linux-kernel - Re: [PATCH 6/6] perf thread-stack: Hide x86 retpolines

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Date:   Fri, 22 Feb 2019 17:53:33 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] perf thread-stack: Hide x86 retpolines

Em Fri, Feb 22, 2019 at 04:42:44PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Wed, Jan 09, 2019 at 11:18:35AM +0200, Adrian Hunter escreveu:
> > +static int thread_stack__x86_retpoline(struct thread_stack *ts,
> > +				       struct perf_sample *sample,
> > +				       struct addr_location *to_al)
> > +{
> > +	struct thread_stack_entry *tse = &ts->stack[ts->cnt - 1];
> > +	struct call_path_root *cpr = ts->crp->cpr;
> > +	struct symbol *sym = tse->cp->sym;
> > +	struct symbol *tsym = to_al->sym;
> > +	struct call_path *cp;
> > +
> > +	if (sym && sym->name && is_x86_retpoline(sym->name)) {
> 
> 
>   CC       /tmp/build/perf/util/scripting-engines/trace-event-perl.o
>   CC       /tmp/build/perf/util/intel-pt.o
>   CC       /tmp/build/perf/util/intel-pt-decoder/intel-pt-log.o
> util/thread-stack.c:780:18: error: address of array 'sym->name' will always evaluate to 'true' [-Werror,-Wpointer-bool-conversion]
>         if (sym && sym->name && is_x86_retpoline(sym->name)) {
>                 ~~ ~~~~~^~~~
> 1 error generated.
> mv: cannot stat '/tmp/build/perf/util/.thread-stack.o.tmp': No such file or directory
> make[4]: *** [/git/linux/tools/build/Makefile.build:96: /tmp/build/perf/util/thread-stack.o] Error 1
> 
> 
> [acme@...co perf]$ pahole -C symbol ~/bin/perf
> struct symbol {
> 	struct rb_node             rb_node;              /*     0    24 */
> 	u64                        start;                /*    24     8 */
> 	u64                        end;                  /*    32     8 */
> 	u16                        namelen;              /*    40     2 */
> 	u8                         type:4;               /*    42: 4  1 */
> 	u8                         binding:4;            /*    42: 0  1 */
> 	u8                         idle:1;               /*    43: 7  1 */
> 	u8                         ignore:1;             /*    43: 6  1 */
> 	u8                         inlined:1;            /*    43: 5  1 */
> 
> 	/* XXX 5 bits hole, try to pack */
> 
> 	u8                         arch_sym;             /*    44     1 */
> 	_Bool                      annotate2;            /*    45     1 */
> 	char                       name[0];              /*    46     0 */
> 
> 	/* size: 48, cachelines: 1, members: 12 */
> 	/* bit holes: 1, sum bit holes: 5 bits */
> 	/* padding: 2 */
> 	/* last cacheline: 48 bytes */
> };
> [acme@...co perf]$
> 
> I'm removing that sym->name test.

For completeness sake, this was one of the compilers where this failed:

clang version 7.0.1 (Fedora 7.0.1-2.fc30)

The systems where it broke:

  18 debian:9                      : FAIL
  19 debian:experimental           : FAIL
  29 fedora:25                     : FAIL
  30 fedora:26                     : FAIL
  31 fedora:27                     : FAIL
  32 fedora:28                     : FAIL
  33 fedora:29                     : FAIL
  34 fedora:30                     : FAIL
  35 fedora:rawhide                : FAIL
  45 opensuse:tumbleweed           : FAIL
  51 ubuntu:16.04                  : FAIL
  58 ubuntu:17.10                  : FAIL
  59 ubuntu:18.04                  : FAIL
  70 ubuntu:18.10                  : FAIL
  71 ubuntu:19.04                  : FAIL

- Arnaldo