[tip: perf/core] perf tools: Avoid 'sample_reg_masks' being const + weak

From: tip-bot2 for Ian Rogers
Date: Tue Oct 15 2019 - 01:33:12 EST

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The following commit has been merged into the perf/core branch of tip:

Commit-ID: 42466b9f29b415c254dc4c2f4618e2a96951a406
Gitweb: https://git.kernel.org/tip/42466b9f29b415c254dc4c2f4618e2a96951a406
Author: Ian Rogers <irogers@xxxxxxxxxx>
AuthorDate: Mon, 30 Sep 2019 17:36:23 -07:00
Committer: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitterDate: Thu, 10 Oct 2019 09:29:33 -03:00

perf tools: Avoid 'sample_reg_masks' being const + weak

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.
In v3, add perf_regs.c for architectures that HAVE_PERF_REGS_SUPPORT but
don't declare sample_regs_masks.

Further notes:

Jiri asked:

"Is this just a precaution or you actualy saw some breakage?"

Ian answered:

"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."

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: clang-built-linux@xxxxxxxxxxxxxxxx
Cc: Guo Ren <guoren@xxxxxxxxxx>
Cc: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Cc: linux-riscv@xxxxxxxxxxxxxxxxxxx
Cc: Mao Han <han_mao@xxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Palmer Dabbelt <palmer@xxxxxxxxxx>
Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Link: http://lore.kernel.org/lkml/20191001003623.255186-1-irogers@xxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
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 296f0ea..37fc637 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-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind.o
diff --git a/tools/perf/arch/arm/util/perf_regs.c b/tools/perf/arch/arm/util/perf_regs.c
new file mode 100644
index 0000000..2864e2e
--- /dev/null
+++ b/tools/perf/arch/arm/util/perf_regs.c
@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "../../util/perf_regs.h"
+
+const struct sample_reg sample_reg_masks[] = {
+ SMPL_REG_END
+};
diff --git a/tools/perf/arch/arm64/util/Build b/tools/perf/arch/arm64/util/Build
index 3cde540..0a7782c 100644
--- a/tools/perf/arch/arm64/util/Build
+++ b/tools/perf/arch/arm64/util/Build
@@ -1,4 +1,5 @@
perf-y += header.o
+perf-y += perf_regs.o
perf-y += sym-handling.o
perf-$(CONFIG_DWARF) += dwarf-regs.o
perf-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind.o
diff --git a/tools/perf/arch/arm64/util/perf_regs.c b/tools/perf/arch/arm64/util/perf_regs.c
new file mode 100644
index 0000000..2864e2e
--- /dev/null
+++ b/tools/perf/arch/arm64/util/perf_regs.c
@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "../../util/perf_regs.h"
+
+const struct sample_reg sample_reg_masks[] = {
+ SMPL_REG_END
+};
diff --git a/tools/perf/arch/csky/util/Build b/tools/perf/arch/csky/util/Build
index 1160bb2..7d30501 100644
--- a/tools/perf/arch/csky/util/Build
+++ b/tools/perf/arch/csky/util/Build
@@ -1,2 +1,4 @@
+perf-y += perf_regs.o
+
perf-$(CONFIG_DWARF) += dwarf-regs.o
perf-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
diff --git a/tools/perf/arch/csky/util/perf_regs.c b/tools/perf/arch/csky/util/perf_regs.c
new file mode 100644
index 0000000..2864e2e
--- /dev/null
+++ b/tools/perf/arch/csky/util/perf_regs.c
@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "../../util/perf_regs.h"
+
+const struct sample_reg sample_reg_masks[] = {
+ SMPL_REG_END
+};
diff --git a/tools/perf/arch/riscv/util/Build b/tools/perf/arch/riscv/util/Build
index 1160bb2..7d30501 100644
--- a/tools/perf/arch/riscv/util/Build
+++ b/tools/perf/arch/riscv/util/Build
@@ -1,2 +1,4 @@
+perf-y += perf_regs.o
+
perf-$(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 0000000..2864e2e
--- /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 22797f0..3d9d0f4 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 0000000..2864e2e
--- /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 ef46c28..e687497 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 2774cec..5ee47ae 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 47fe34e..e014c2c 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))

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