Messages in this thread | | | Date | Sun, 29 Sep 2019 23:05:14 +0200 | From | Jiri Olsa <> | Subject | Re: [PATCH v2] perf tools: avoid sample_reg_masks being const + weak |
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On Fri, Sep 27, 2019 at 02:43:41PM -0700, Ian Rogers wrote: > Being const + weak breaks with some compilers that constant-propagate > from the weak symbol. This behavior is outside of the specification, but > in LLVM is chosen to match GCC's behavior. > > LLVM's implementation was set in this patch: > https://github.com/llvm/llvm-project/commit/f49573d1eedcf1e44893d5a062ac1b72c8419646 > A const + weak symbol is set to be weak_odr: > https://llvm.org/docs/LangRef.html > ODR is one definition rule, and given there is one constant definition > constant-propagation is possible. It is possible to get this code to > miscompile with LLVM when applying link time optimization. As compilers > become more aggressive, this is likely to break in more instances. > > Move the definition of sample_reg_masks to the conditional part of > perf_regs.h and guard usage with HAVE_PERF_REGS_SUPPORT. This avoids the > weak symbol. > > Fix an issue when HAVE_PERF_REGS_SUPPORT isn't defined from patch v1. > > Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
thanks, jirka
> --- > tools/perf/util/parse-regs-options.c | 8 ++++++-- > tools/perf/util/perf_regs.c | 4 ---- > tools/perf/util/perf_regs.h | 4 ++-- > 3 files changed, 8 insertions(+), 8 deletions(-) > > diff --git a/tools/perf/util/parse-regs-options.c b/tools/perf/util/parse-regs-options.c > index ef46c2848808..e687497b3aac 100644 > --- a/tools/perf/util/parse-regs-options.c > +++ b/tools/perf/util/parse-regs-options.c > @@ -13,7 +13,7 @@ static int > __parse_regs(const struct option *opt, const char *str, int unset, bool intr) > { > uint64_t *mode = (uint64_t *)opt->value; > - const struct sample_reg *r; > + const struct sample_reg *r = NULL; > char *s, *os = NULL, *p; > int ret = -1; > uint64_t mask; > @@ -46,19 +46,23 @@ __parse_regs(const struct option *opt, const char *str, int unset, bool intr) > > if (!strcmp(s, "?")) { > fprintf(stderr, "available registers: "); > +#ifdef HAVE_PERF_REGS_SUPPORT > for (r = sample_reg_masks; r->name; r++) { > if (r->mask & mask) > fprintf(stderr, "%s ", r->name); > } > +#endif > fputc('\n', stderr); > /* just printing available regs */ > return -1; > } > +#ifdef HAVE_PERF_REGS_SUPPORT > for (r = sample_reg_masks; r->name; r++) { > if ((r->mask & mask) && !strcasecmp(s, r->name)) > break; > } > - if (!r->name) { > +#endif > + if (!r || !r->name) { > ui__warning("Unknown register \"%s\", check man page or run \"perf record %s?\"\n", > s, intr ? "-I" : "--user-regs="); > goto error; > diff --git a/tools/perf/util/perf_regs.c b/tools/perf/util/perf_regs.c > index 2774cec1f15f..5ee47ae1509c 100644 > --- a/tools/perf/util/perf_regs.c > +++ b/tools/perf/util/perf_regs.c > @@ -3,10 +3,6 @@ > #include "perf_regs.h" > #include "event.h" > > -const struct sample_reg __weak sample_reg_masks[] = { > - SMPL_REG_END > -}; > - > int __weak arch_sdt_arg_parse_op(char *old_op __maybe_unused, > char **new_op __maybe_unused) > { > diff --git a/tools/perf/util/perf_regs.h b/tools/perf/util/perf_regs.h > index 47fe34e5f7d5..e014c2c038f4 100644 > --- a/tools/perf/util/perf_regs.h > +++ b/tools/perf/util/perf_regs.h > @@ -15,8 +15,6 @@ struct sample_reg { > #define SMPL_REG2(n, b) { .name = #n, .mask = 3ULL << (b) } > #define SMPL_REG_END { .name = NULL } > > -extern const struct sample_reg sample_reg_masks[]; > - > enum { > SDT_ARG_VALID = 0, > SDT_ARG_SKIP, > @@ -27,6 +25,8 @@ uint64_t arch__intr_reg_mask(void); > uint64_t arch__user_reg_mask(void); > > #ifdef HAVE_PERF_REGS_SUPPORT > +extern const struct sample_reg sample_reg_masks[]; > + > #include <perf_regs.h> > > #define DWARF_MINIMAL_REGS ((1ULL << PERF_REG_IP) | (1ULL << PERF_REG_SP)) > -- > 2.23.0.444.g18eeb5a265-goog >
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