arch/arm64/kernel/perf_regs.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/compat.h>
   3 #include <linux/errno.h>
   4 #include <linux/kernel.h>
   5 #include <linux/perf_event.h>
   6 #include <linux/bug.h>
   7 #include <linux/sched/task_stack.h>
   8
   9 #include <asm/perf_regs.h>
  10 #include <asm/ptrace.h>
  11
  12 u64 perf_reg_value(struct pt_regs *regs, int idx)
  13 {
  14         if (WARN_ON_ONCE((u32)idx >= PERF_REG_ARM64_MAX))
  15                 return 0;
  16
  17         /*
  18          * Our handling of compat tasks (PERF_SAMPLE_REGS_ABI_32) is weird, but
  19          * we're stuck with it for ABI compatibility reasons.
  20          *
  21          * For a 32-bit consumer inspecting a 32-bit task, then it will look at
  22          * the first 16 registers (see arch/arm/include/uapi/asm/perf_regs.h).
  23          * These correspond directly to a prefix of the registers saved in our
  24          * 'struct pt_regs', with the exception of the PC, so we copy that down
  25          * (x15 corresponds to SP_hyp in the architecture).
  26          *
  27          * So far, so good.
  28          *
  29          * The oddity arises when a 64-bit consumer looks at a 32-bit task and
  30          * asks for registers beyond PERF_REG_ARM_MAX. In this case, we return
  31          * SP_usr, LR_usr and PC in the positions where the AArch64 SP, LR and
  32          * PC registers would normally live. The initial idea was to allow a
  33          * 64-bit unwinder to unwind a 32-bit task and, although it's not clear
  34          * how well that works in practice, somebody might be relying on it.
  35          *
  36          * At the time we make a sample, we don't know whether the consumer is
  37          * 32-bit or 64-bit, so we have to cater for both possibilities.
  38          */
  39         if (compat_user_mode(regs)) {
  40                 if ((u32)idx == PERF_REG_ARM64_SP)
  41                         return regs->compat_sp;
  42                 if ((u32)idx == PERF_REG_ARM64_LR)
  43                         return regs->compat_lr;
  44                 if (idx == 15)
  45                         return regs->pc;
  46         }
  47
  48         if ((u32)idx == PERF_REG_ARM64_SP)
  49                 return regs->sp;
  50
  51         if ((u32)idx == PERF_REG_ARM64_PC)
  52                 return regs->pc;
  53
  54         return regs->regs[idx];
  55 }
  56
  57 #define REG_RESERVED (~((1ULL << PERF_REG_ARM64_MAX) - 1))
  58
  59 int perf_reg_validate(u64 mask)
  60 {
  61         if (!mask || mask & REG_RESERVED)
  62                 return -EINVAL;
  63
  64         return 0;
  65 }
  66
  67 u64 perf_reg_abi(struct task_struct *task)
  68 {
  69         if (is_compat_thread(task_thread_info(task)))
  70                 return PERF_SAMPLE_REGS_ABI_32;
  71         else
  72                 return PERF_SAMPLE_REGS_ABI_64;
  73 }
  74
  75 void perf_get_regs_user(struct perf_regs *regs_user,
  76                         struct pt_regs *regs)
  77 {
  78         regs_user->regs = task_pt_regs(current);
  79         regs_user->abi = perf_reg_abi(current);
  80 }