Messages in this thread | | | Date | Tue, 8 Oct 2019 14:31:04 +0200 | From | Jiri Olsa <> | Subject | Re: [PATCH v3] perf tools: avoid sample_reg_masks being const + weak |
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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?
> > 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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