On x86_64, at least, task_pt_regs may be only partially initialized
in many contexts, so x86_64 should not use it without extra care
from interrupt context, let alone NMI context.

This will allow x86_64 to override the logic and will supply some
scratch space to use to make a cleaner copy of user regs.

Tested-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: chenggang.qcg@taobao.com
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Jean Pihet <jean.pihet@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mark Salter <msalter@redhat.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/e431cd4c18c2e1c44c774f10758527fb2d1025c4.1420396372.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

The current perf_regs code relies on sp and pc sitting just off the end
of the pt_regs->regs array. This is ugly and fragile, so this patch
checks for these register explicitly and returns the appropriate field.

Acked-by: Jean Pihet <jean.pihet@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

Recent arm64 builds using CONFIG_ARM64_64K_PAGES are failing with:

  arch/arm64/kernel/perf_regs.c: In function ‘perf_reg_abi’:
  arch/arm64/kernel/perf_regs.c:41:2: error: implicit declaration of function ‘is_compat_thread’

  arch/arm64/kernel/perf_event.c:1398:2: error: unknown type name ‘compat_uptr_t’

This is due to some recent arm64 perf commits with compat support:

  commit 23c7d70d55c6d9:
    ARM64: perf: add support for frame pointer unwinding in compat mode

  commit 2ee0d7fd36a3f8:
    ARM64: perf: add support for perf registers API

Those patches make the arm64 kernel unbuildable if CONFIG_COMPAT is not
defined and CONFIG_ARM64_64K_PAGES depends on !CONFIG_COMPAT. This patch
allows the arm64 kernel to build with and without CONFIG_COMPAT.

Signed-off-by: Mark Salter <msalter@redhat.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

This patch implements the functions required for the perf registers API,
allowing the perf tool to interface kernel register dumps with libunwind
in order to provide userspace backtracing.
Compat mode is also supported.

Only the general purpose user space registers are exported, i.e.:
 PERF_REG_ARM_X0,
 ...
 PERF_REG_ARM_X28,
 PERF_REG_ARM_FP,
 PERF_REG_ARM_LR,
 PERF_REG_ARM_SP,
 PERF_REG_ARM_PC
and not the PERF_REG_ARM_V* registers.

Signed-off-by: Jean Pihet <jean.pihet@linaro.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>