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authorIan Rogers <irogers@google.com>2019-09-30 17:36:23 -0700
committerArnaldo Carvalho de Melo <acme@redhat.com>2019-10-10 09:29:33 -0300
commit42466b9f29b415c254dc4c2f4618e2a96951a406 (patch)
tree43dadb26b8eccb3d0ad1496a647aa8246fdb390f /tools/perf/arch/csky
parentperf beauty: Introduce strtoul() for x86 MSRs (diff)
downloadlinux-dev-42466b9f29b415c254dc4c2f4618e2a96951a406.tar.xz
linux-dev-42466b9f29b415c254dc4c2f4618e2a96951a406.zip
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>
Diffstat (limited to 'tools/perf/arch/csky')
-rw-r--r--tools/perf/arch/csky/util/Build2
-rw-r--r--tools/perf/arch/csky/util/perf_regs.c6
2 files changed, 8 insertions, 0 deletions
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
+};