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42466b9f29
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:
f49573d1ee
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>
54 lines
1.2 KiB
C
54 lines
1.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __PERF_REGS_H
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#define __PERF_REGS_H
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#include <linux/types.h>
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#include <linux/compiler.h>
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struct regs_dump;
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struct sample_reg {
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const char *name;
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uint64_t mask;
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};
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#define SMPL_REG(n, b) { .name = #n, .mask = 1ULL << (b) }
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#define SMPL_REG2(n, b) { .name = #n, .mask = 3ULL << (b) }
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#define SMPL_REG_END { .name = NULL }
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enum {
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SDT_ARG_VALID = 0,
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SDT_ARG_SKIP,
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};
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int arch_sdt_arg_parse_op(char *old_op, char **new_op);
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uint64_t arch__intr_reg_mask(void);
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uint64_t arch__user_reg_mask(void);
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#ifdef HAVE_PERF_REGS_SUPPORT
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extern const struct sample_reg sample_reg_masks[];
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#include <perf_regs.h>
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#define DWARF_MINIMAL_REGS ((1ULL << PERF_REG_IP) | (1ULL << PERF_REG_SP))
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int perf_reg_value(u64 *valp, struct regs_dump *regs, int id);
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#else
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#define PERF_REGS_MASK 0
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#define PERF_REGS_MAX 0
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#define DWARF_MINIMAL_REGS PERF_REGS_MASK
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static inline const char *perf_reg_name(int id __maybe_unused)
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{
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return NULL;
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}
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static inline int perf_reg_value(u64 *valp __maybe_unused,
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struct regs_dump *regs __maybe_unused,
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int id __maybe_unused)
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{
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return 0;
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}
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#endif /* HAVE_PERF_REGS_SUPPORT */
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#endif /* __PERF_REGS_H */
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