renegade-project/linux-next
2
0
Fork 0
mirror of https://github.com/edk2-porting/linux-next.git synced 2024-12-27 22:53:55 +08:00
Code
32fdc2ca7e
linux-next/tools/perf/arch/arm64
History
Ian Rogers 42466b9f29 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:

  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>
2019-10-10 09:29:33 -03:00
..
annotate perf annotate: Fix arch specific ->init() failure errors 2019-09-30 17:30:03 -03:00
entry/syscalls perf arm64: Fix mksyscalltbl when system kernel headers are ahead of the kernel 2019-05-28 09:49:03 -03:00
include perf tools arm64: Add libdw DWARF post unwind support for ARM64 2018-03-16 13:53:46 -03:00
tests perf tests arm64: Compile tests unconditionally 2019-06-17 15:57:16 -03:00
util perf tools: Avoid 'sample_reg_masks' being const + weak 2019-10-10 09:29:33 -03:00
Build perf tests arm64: Compile tests unconditionally 2019-06-17 15:57:16 -03:00
Makefile perf arm64: Fix include path for asm-generic/unistd.h 2018-08-30 14:49:24 -03:00