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@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: clang-built-linux@googlegroups.com
Cc: Guo Ren <guoren@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: linux-riscv@lists.infradead.org
Cc: Mao Han <han_mao@c-sky.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20191001003623.255186-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

13 files changed, 46 insertions, 8 deletions

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))