root/arch/riscv/kernel/perf_callchain.c

DEFINITIONS

1. user_backtrace
2. perf_callchain_user
3. fill_callchain
4. perf_callchain_kernel

   1 // SPDX-License-Identifier: GPL-2.0
   2 /* Copyright (C) 2019 Hangzhou C-SKY Microsystems co.,ltd. */
   3 
   4 #include <linux/perf_event.h>
   5 #include <linux/uaccess.h>
   6 
   7 /* Kernel callchain */
   8 struct stackframe {
   9         unsigned long fp;
  10         unsigned long ra;
  11 };
  12 
  13 /*
  14  * Get the return address for a single stackframe and return a pointer to the
  15  * next frame tail.
  16  */
  17 static unsigned long user_backtrace(struct perf_callchain_entry_ctx *entry,
  18                                     unsigned long fp, unsigned long reg_ra)
  19 {
  20         struct stackframe buftail;
  21         unsigned long ra = 0;
  22         unsigned long *user_frame_tail =
  23                         (unsigned long *)(fp - sizeof(struct stackframe));
  24 
  25         /* Check accessibility of one struct frame_tail beyond */
  26         if (!access_ok(user_frame_tail, sizeof(buftail)))
  27                 return 0;
  28         if (__copy_from_user_inatomic(&buftail, user_frame_tail,
  29                                       sizeof(buftail)))
  30                 return 0;
  31 
  32         if (reg_ra != 0)
  33                 ra = reg_ra;
  34         else
  35                 ra = buftail.ra;
  36 
  37         fp = buftail.fp;
  38         if (ra != 0)
  39                 perf_callchain_store(entry, ra);
  40         else
  41                 return 0;
  42 
  43         return fp;
  44 }
  45 
  46 /*
  47  * This will be called when the target is in user mode
  48  * This function will only be called when we use
  49  * "PERF_SAMPLE_CALLCHAIN" in
  50  * kernel/events/core.c:perf_prepare_sample()
  51  *
  52  * How to trigger perf_callchain_[user/kernel] :
  53  * $ perf record -e cpu-clock --call-graph fp ./program
  54  * $ perf report --call-graph
  55  *
  56  * On RISC-V platform, the program being sampled and the C library
  57  * need to be compiled with -fno-omit-frame-pointer, otherwise
  58  * the user stack will not contain function frame.
  59  */
  60 void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
  61                          struct pt_regs *regs)
  62 {
  63         unsigned long fp = 0;
  64 
  65         /* RISC-V does not support perf in guest mode. */
  66         if (perf_guest_cbs && perf_guest_cbs->is_in_guest())
  67                 return;
  68 
  69         fp = regs->s0;
  70         perf_callchain_store(entry, regs->sepc);
  71 
  72         fp = user_backtrace(entry, fp, regs->ra);
  73         while (fp && !(fp & 0x3) && entry->nr < entry->max_stack)
  74                 fp = user_backtrace(entry, fp, 0);
  75 }
  76 
  77 bool fill_callchain(unsigned long pc, void *entry)
  78 {
  79         return perf_callchain_store(entry, pc);
  80 }
  81 
  82 void notrace walk_stackframe(struct task_struct *task,
  83         struct pt_regs *regs, bool (*fn)(unsigned long, void *), void *arg);
  84 void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
  85                            struct pt_regs *regs)
  86 {
  87         /* RISC-V does not support perf in guest mode. */
  88         if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
  89                 pr_warn("RISC-V does not support perf in guest mode!");
  90                 return;
  91         }
  92 
  93         walk_stackframe(NULL, regs, fill_callchain, entry);
  94 }