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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>
46 lines
800 B
C
46 lines
800 B
C
// SPDX-License-Identifier: GPL-2.0
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#include <errno.h>
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#include "perf_regs.h"
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#include "event.h"
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int __weak arch_sdt_arg_parse_op(char *old_op __maybe_unused,
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char **new_op __maybe_unused)
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{
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return SDT_ARG_SKIP;
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}
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uint64_t __weak arch__intr_reg_mask(void)
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{
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return PERF_REGS_MASK;
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}
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uint64_t __weak arch__user_reg_mask(void)
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{
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return PERF_REGS_MASK;
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}
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#ifdef HAVE_PERF_REGS_SUPPORT
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int perf_reg_value(u64 *valp, struct regs_dump *regs, int id)
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{
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int i, idx = 0;
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u64 mask = regs->mask;
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if (regs->cache_mask & (1ULL << id))
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goto out;
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if (!(mask & (1ULL << id)))
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return -EINVAL;
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for (i = 0; i < id; i++) {
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if (mask & (1ULL << i))
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idx++;
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}
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regs->cache_mask |= (1ULL << id);
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regs->cache_regs[id] = regs->regs[idx];
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out:
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*valp = regs->cache_regs[id];
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return 0;
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}
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#endif
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