Messages in this thread | | | From | Ian Rogers <> | Date | Wed, 9 Oct 2019 16:07:37 -0700 | Subject | Re: [PATCH v3] perf tools: avoid sample_reg_masks being const + weak |
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On Tue, Oct 8, 2019 at 5:31 AM Jiri Olsa <jolsa@redhat.com> wrote: > > On Mon, Sep 30, 2019 at 05:36:23PM -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. > > is this just aprecaution or you actualy saw some breakage?
We saw a breakage with clang with thinlto enabled for linking. Our compiler team had recently seen, and were surprised by, a similar issue and were able to dig out the weak ODR issue.
Thanks, Ian
> > 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. > > In v3, add perf_regs.c for architectures that HAVE_PERF_REGS_SUPPORT but > > don't declare sample_regs_masks. > > looks good to me (again ;-)), let's see if it passes Arnaldo's farm > > thanks, > jirka > > > > > Signed-off-by: Ian Rogers <irogers@google.com> > > --- > > tools/perf/arch/arm/util/Build | 2 ++ > > tools/perf/arch/arm/util/perf_regs.c | 6 ++++++ > > tools/perf/arch/arm64/util/Build | 1 + > > tools/perf/arch/arm64/util/perf_regs.c | 6 ++++++ > > tools/perf/arch/csky/util/Build | 2 ++ > > tools/perf/arch/csky/util/perf_regs.c | 6 ++++++ > > tools/perf/arch/riscv/util/Build | 2 ++ > > tools/perf/arch/riscv/util/perf_regs.c | 6 ++++++ > > tools/perf/arch/s390/util/Build | 1 + > > tools/perf/arch/s390/util/perf_regs.c | 6 ++++++ > > tools/perf/util/parse-regs-options.c | 8 ++++++-- > > tools/perf/util/perf_regs.c | 4 ---- > > tools/perf/util/perf_regs.h | 4 ++-- > > 13 files changed, 46 insertions(+), 8 deletions(-) > > create mode 100644 tools/perf/arch/arm/util/perf_regs.c > > create mode 100644 tools/perf/arch/arm64/util/perf_regs.c > > create mode 100644 tools/perf/arch/csky/util/perf_regs.c > > create mode 100644 tools/perf/arch/riscv/util/perf_regs.c > > create mode 100644 tools/perf/arch/s390/util/perf_regs.c > > > > diff --git a/tools/perf/arch/arm/util/Build b/tools/perf/arch/arm/util/Build > > index 296f0eac5e18..37fc63708966 100644 > > --- a/tools/perf/arch/arm/util/Build > > +++ b/tools/perf/arch/arm/util/Build > > @@ -1,3 +1,5 @@ > > +perf-y += perf_regs.o > > + > > perf-$(CONFIG_DWARF) += dwarf-regs.o > > > > perf-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind.o > > diff --git a/tools/perf/arch/arm/util/perf_regs.c b/tools/perf/arch/arm/util/perf_regs.c > > new file mode 100644 > > index 000000000000..2864e2e3776d > > --- /dev/null > > +++ b/tools/perf/arch/arm/util/perf_regs.c > > @@ -0,0 +1,6 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > +#include "../../util/perf_regs.h" > > + > > +const struct sample_reg sample_reg_masks[] = { > > + SMPL_REG_END > > +}; > > diff --git a/tools/perf/arch/arm64/util/Build b/tools/perf/arch/arm64/util/Build > > index 3cde540d2fcf..0a7782c61209 100644 > > --- a/tools/perf/arch/arm64/util/Build > > +++ b/tools/perf/arch/arm64/util/Build > > @@ -1,4 +1,5 @@ > > perf-y += header.o > > +perf-y += perf_regs.o > > perf-y += sym-handling.o > > perf-$(CONFIG_DWARF) += dwarf-regs.o > > perf-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind.o > > diff --git a/tools/perf/arch/arm64/util/perf_regs.c b/tools/perf/arch/arm64/util/perf_regs.c > > new file mode 100644 > > index 000000000000..2864e2e3776d > > --- /dev/null > > +++ b/tools/perf/arch/arm64/util/perf_regs.c > > @@ -0,0 +1,6 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > +#include "../../util/perf_regs.h" > > + > > +const struct sample_reg sample_reg_masks[] = { > > + SMPL_REG_END > > +}; > > diff --git a/tools/perf/arch/csky/util/Build b/tools/perf/arch/csky/util/Build > > index 1160bb2332ba..7d3050134ae0 100644 > > --- a/tools/perf/arch/csky/util/Build > > +++ b/tools/perf/arch/csky/util/Build > > @@ -1,2 +1,4 @@ > > +perf-y += perf_regs.o > > + > > perf-$(CONFIG_DWARF) += dwarf-regs.o > > perf-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o > > diff --git a/tools/perf/arch/csky/util/perf_regs.c b/tools/perf/arch/csky/util/perf_regs.c > > new file mode 100644 > > index 000000000000..2864e2e3776d > > --- /dev/null > > +++ b/tools/perf/arch/csky/util/perf_regs.c > > @@ -0,0 +1,6 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > +#include "../../util/perf_regs.h" > > + > > +const struct sample_reg sample_reg_masks[] = { > > + SMPL_REG_END > > +}; > > diff --git a/tools/perf/arch/riscv/util/Build b/tools/perf/arch/riscv/util/Build > > index 1160bb2332ba..7d3050134ae0 100644 > > --- a/tools/perf/arch/riscv/util/Build > > +++ b/tools/perf/arch/riscv/util/Build > > @@ -1,2 +1,4 @@ > > +perf-y += perf_regs.o > > + > > perf-$(CONFIG_DWARF) += dwarf-regs.o > > perf-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o > > diff --git a/tools/perf/arch/riscv/util/perf_regs.c b/tools/perf/arch/riscv/util/perf_regs.c > > new file mode 100644 > > index 000000000000..2864e2e3776d > > --- /dev/null > > +++ b/tools/perf/arch/riscv/util/perf_regs.c > > @@ -0,0 +1,6 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > +#include "../../util/perf_regs.h" > > + > > +const struct sample_reg sample_reg_masks[] = { > > + SMPL_REG_END > > +}; > > diff --git a/tools/perf/arch/s390/util/Build b/tools/perf/arch/s390/util/Build > > index 22797f043b84..3d9d0f4f72ca 100644 > > --- a/tools/perf/arch/s390/util/Build > > +++ b/tools/perf/arch/s390/util/Build > > @@ -1,5 +1,6 @@ > > perf-y += header.o > > perf-y += kvm-stat.o > > +perf-y += perf_regs.o > > > > perf-$(CONFIG_DWARF) += dwarf-regs.o > > perf-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o > > diff --git a/tools/perf/arch/s390/util/perf_regs.c b/tools/perf/arch/s390/util/perf_regs.c > > new file mode 100644 > > index 000000000000..2864e2e3776d > > --- /dev/null > > +++ b/tools/perf/arch/s390/util/perf_regs.c > > @@ -0,0 +1,6 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > +#include "../../util/perf_regs.h" > > + > > +const struct sample_reg sample_reg_masks[] = { > > + SMPL_REG_END > > +}; > > 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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