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Linux/arch/mips/oprofile/backtrace.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 #include <linux/oprofile.h>
  3 #include <linux/sched.h>
  4 #include <linux/mm.h>
  5 #include <linux/uaccess.h>
  6 #include <asm/ptrace.h>
  7 #include <asm/stacktrace.h>
  8 #include <linux/stacktrace.h>
  9 #include <linux/kernel.h>
 10 #include <asm/sections.h>
 11 #include <asm/inst.h>
 12 
 13 struct stackframe {
 14         unsigned long sp;
 15         unsigned long pc;
 16         unsigned long ra;
 17 };
 18 
 19 static inline int get_mem(unsigned long addr, unsigned long *result)
 20 {
 21         unsigned long *address = (unsigned long *) addr;
 22         if (!access_ok(VERIFY_READ, address, sizeof(unsigned long)))
 23                 return -1;
 24         if (__copy_from_user_inatomic(result, address, sizeof(unsigned long)))
 25                 return -3;
 26         return 0;
 27 }
 28 
 29 /*
 30  * These two instruction helpers were taken from process.c
 31  */
 32 static inline int is_ra_save_ins(union mips_instruction *ip)
 33 {
 34         /* sw / sd $ra, offset($sp) */
 35         return (ip->i_format.opcode == sw_op || ip->i_format.opcode == sd_op)
 36                 && ip->i_format.rs == 29 && ip->i_format.rt == 31;
 37 }
 38 
 39 static inline int is_sp_move_ins(union mips_instruction *ip)
 40 {
 41         /* addiu/daddiu sp,sp,-imm */
 42         if (ip->i_format.rs != 29 || ip->i_format.rt != 29)
 43                 return 0;
 44         if (ip->i_format.opcode == addiu_op || ip->i_format.opcode == daddiu_op)
 45                 return 1;
 46         return 0;
 47 }
 48 
 49 /*
 50  * Looks for specific instructions that mark the end of a function.
 51  * This usually means we ran into the code area of the previous function.
 52  */
 53 static inline int is_end_of_function_marker(union mips_instruction *ip)
 54 {
 55         /* jr ra */
 56         if (ip->r_format.func == jr_op && ip->r_format.rs == 31)
 57                 return 1;
 58         /* lui gp */
 59         if (ip->i_format.opcode == lui_op && ip->i_format.rt == 28)
 60                 return 1;
 61         return 0;
 62 }
 63 
 64 /*
 65  * TODO for userspace stack unwinding:
 66  * - handle cases where the stack is adjusted inside a function
 67  *     (generally doesn't happen)
 68  * - find optimal value for max_instr_check
 69  * - try to find a better way to handle leaf functions
 70  */
 71 
 72 static inline int unwind_user_frame(struct stackframe *old_frame,
 73                                     const unsigned int max_instr_check)
 74 {
 75         struct stackframe new_frame = *old_frame;
 76         off_t ra_offset = 0;
 77         size_t stack_size = 0;
 78         unsigned long addr;
 79 
 80         if (old_frame->pc == 0 || old_frame->sp == 0 || old_frame->ra == 0)
 81                 return -9;
 82 
 83         for (addr = new_frame.pc; (addr + max_instr_check > new_frame.pc)
 84                 && (!ra_offset || !stack_size); --addr) {
 85                 union mips_instruction ip;
 86 
 87                 if (get_mem(addr, (unsigned long *) &ip))
 88                         return -11;
 89 
 90                 if (is_sp_move_ins(&ip)) {
 91                         int stack_adjustment = ip.i_format.simmediate;
 92                         if (stack_adjustment > 0)
 93                                 /* This marks the end of the previous function,
 94                                    which means we overran. */
 95                                 break;
 96                         stack_size = (unsigned long) stack_adjustment;
 97                 } else if (is_ra_save_ins(&ip)) {
 98                         int ra_slot = ip.i_format.simmediate;
 99                         if (ra_slot < 0)
100                                 /* This shouldn't happen. */
101                                 break;
102                         ra_offset = ra_slot;
103                 } else if (is_end_of_function_marker(&ip))
104                         break;
105         }
106 
107         if (!ra_offset || !stack_size)
108                 goto done;
109 
110         if (ra_offset) {
111                 new_frame.ra = old_frame->sp + ra_offset;
112                 if (get_mem(new_frame.ra, &(new_frame.ra)))
113                         return -13;
114         }
115 
116         if (stack_size) {
117                 new_frame.sp = old_frame->sp + stack_size;
118                 if (get_mem(new_frame.sp, &(new_frame.sp)))
119                         return -14;
120         }
121 
122         if (new_frame.sp > old_frame->sp)
123                 return -2;
124 
125 done:
126         new_frame.pc = old_frame->ra;
127         *old_frame = new_frame;
128 
129         return 0;
130 }
131 
132 static inline void do_user_backtrace(unsigned long low_addr,
133                                      struct stackframe *frame,
134                                      unsigned int depth)
135 {
136         const unsigned int max_instr_check = 512;
137         const unsigned long high_addr = low_addr + THREAD_SIZE;
138 
139         while (depth-- && !unwind_user_frame(frame, max_instr_check)) {
140                 oprofile_add_trace(frame->ra);
141                 if (frame->sp < low_addr || frame->sp > high_addr)
142                         break;
143         }
144 }
145 
146 #ifndef CONFIG_KALLSYMS
147 static inline void do_kernel_backtrace(unsigned long low_addr,
148                                        struct stackframe *frame,
149                                        unsigned int depth) { }
150 #else
151 static inline void do_kernel_backtrace(unsigned long low_addr,
152                                        struct stackframe *frame,
153                                        unsigned int depth)
154 {
155         while (depth-- && frame->pc) {
156                 frame->pc = unwind_stack_by_address(low_addr,
157                                                     &(frame->sp),
158                                                     frame->pc,
159                                                     &(frame->ra));
160                 oprofile_add_trace(frame->ra);
161         }
162 }
163 #endif
164 
165 void notrace op_mips_backtrace(struct pt_regs *const regs, unsigned int depth)
166 {
167         struct stackframe frame = { .sp = regs->regs[29],
168                                     .pc = regs->cp0_epc,
169                                     .ra = regs->regs[31] };
170         const int userspace = user_mode(regs);
171         const unsigned long low_addr = ALIGN(frame.sp, THREAD_SIZE);
172 
173         if (userspace)
174                 do_user_backtrace(low_addr, &frame, depth);
175         else
176                 do_kernel_backtrace(low_addr, &frame, depth);
177 }
178 

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