linux-kernel - Re: [PATCH] perf tools: set kernel end address properly

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Date:   Thu, 19 Apr 2018 18:33:13 -0500
From:   Kim Phillips <kim.phillips@....com>
To:     Namhyung Kim <namhyung@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Will Deacon <will.deacon@....com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Jiri Olsa <jolsa@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, <kernel-team@....com>
Subject: Re: [PATCH] perf tools: set kernel end address properly

On Thu, 19 Apr 2018 11:54:24 +0900
Namhyung Kim <namhyung@...nel.org> wrote:

> On Wed, Apr 18, 2018 at 07:37:59PM -0500, Kim Phillips wrote:
> > diff --git a/tools/perf/arch/arm64/util/sym-handling.c b/tools/perf/arch/arm64/util/sym-handling.c
> > index 0051b1ee8450..5c4a2e208bbc 100644
> > --- a/tools/perf/arch/arm64/util/sym-handling.c
> > +++ b/tools/perf/arch/arm64/util/sym-handling.c
> > @@ -20,3 +20,16 @@ bool elf__needs_adjust_symbols(GElf_Ehdr ehdr)
> >                ehdr.e_type == ET_DYN;
> >  }
> >  #endif
> > +
> > +const char *arch__normalize_symbol_name(const char *name)
> > +{
> > +       /* 
> > +        * arm64 kernels compensating for a CPU erratum can put up a 
> > +        * module_emit_adrp_veneer in place of a module_emit_plt_entry
> > +        */
> > +       if (name && strlen(name) >= 23 &&
> > +           !strncmp(name, "module_emit_adrp_veneer", 23))
> > +               return "module_emit_plt_entry";
> > +
> > +       return name;
> > +}
> 
> I don't know it's always preferable or just for the test.  It it's the
> latter it may be better to move it to the test code.

AFACT, the veneer is a moniker and doesn't technically exist, and
shouldn't be being looked-up.  Both chunks of this diff are needed to
pass perf test 1: this chunk above is because in
arch__normalize_symbol_name(), we squash the perf test 1's "<veneer>
not in *kallsyms*" problem, and in the below chunk, we prevent it
coming up when the test code iterates over the *vmlinux* symbols. I.e.
we need to prevent the veneer from coming up in both kallsyms *and*
vmlinux.

> > diff --git a/tools/perf/tests/vmlinux-kallsyms.c b/tools/perf/tests/vmlinux-kallsyms.c
> > index 1e5adb65632a..07064e76947d 100644
> > --- a/tools/perf/tests/vmlinux-kallsyms.c
> > +++ b/tools/perf/tests/vmlinux-kallsyms.c
> > @@ -163,6 +163,29 @@ int test__vmlinux_matches_kallsyms(struct test *test __maybe_unused, int subtest
> >  
> >                                 continue;
> >                         }
> > +               } else if (pair) {
> > +                       s64 skew = mem_start - UM(pair->start);
> > +                       struct map *kmap = map_groups__find(&kallsyms.kmaps, type, mem_start);
> > +                       struct map *vmap = map_groups__find(&vmlinux.kmaps, type, mem_start);
> > +
> > +                       /* 
> > +                        * arm64 kernels compensating for a CPU erratum can put up a 
> > +                        * module_emit_adrp_veneer in place of a module_emit_plt_entry
> > +                        */
> > +                       if (llabs(skew) < page_size)
> 
> It seems that we needs to check it's the ARM64 at least.  If it's a

OK.

> rare case we might need to add more paranoid checks.

It's certainly rare: Adding the authors of the veneer to cc for
comments:

Will, Ard, how probable are veneer-style symbols such as the
one introduced in commit a257e0257 "arm64/kernel: don't ban ADRP to
work around Cortex-A53 erratum #843419" to happen again in the future?

I would have thought WARNing on within-a-pagesize would be OK,
Namhyung.  Are you suggesting checking instead for a hardcoded veneer
symbol string?

Thanks,

Kim

> > +                       {
> > +                               pr_debug("NO ERR FOR SKEW %ld: %#" PRIx64 ": diff start addr v: %s k: %#" PRIx64 " %s\n",
> > +                                        skew, mem_start, sym->name, UM(pair->start), pair->name);
> > +                               continue;
> > +                       }
> > +
> > +                       pr_debug("ERR : %#" PRIx64 ": diff start addr v: %s k: %#" PRIx64 " %s\n",
> > +                                mem_start, sym->name, UM(pair->start), pair->name);
> > +
> > +                       if (kmap && vmap) {
> > +                               pr_debug("    : map v: %s k: %s\n",
> > +                                        vmap->dso->short_name, kmap->dso->short_name);
> > +                       }
> >                 } else
> >                         pr_debug("ERR : %#" PRIx64 ": %s not on kallsyms\n",
> >                                  mem_start, sym->name);