1 files changed, 177 insertions, 0 deletions

diff --git a/arch/mips/oprofile/backtrace.c b/arch/mips/oprofile/backtrace.c
new file mode 100644
index 000000000..07d98ba7f
--- /dev/null
+++ b/arch/mips/oprofile/backtrace.c
@@ -0,0 +1,177 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/oprofile.h>
+#include <linux/sched.h>
+#include <linux/mm.h>
+#include <linux/uaccess.h>
+#include <asm/ptrace.h>
+#include <asm/stacktrace.h>
+#include <linux/stacktrace.h>
+#include <linux/kernel.h>
+#include <asm/sections.h>
+#include <asm/inst.h>
+
+struct stackframe {
+        unsigned long sp;
+        unsigned long pc;
+        unsigned long ra;
+};
+
+static inline int get_mem(unsigned long addr, unsigned long *result)
+{
+        unsigned long *address = (unsigned long *) addr;
+        if (!access_ok(address, sizeof(unsigned long)))
+                return -1;
+        if (__copy_from_user_inatomic(result, address, sizeof(unsigned long)))
+                return -3;
+        return 0;
+}
+
+/*
+ * These two instruction helpers were taken from process.c
+ */
+static inline int is_ra_save_ins(union mips_instruction *ip)
+{
+        /* sw / sd $ra, offset($sp) */
+        return (ip->i_format.opcode == sw_op || ip->i_format.opcode == sd_op)
+                && ip->i_format.rs == 29 && ip->i_format.rt == 31;
+}
+
+static inline int is_sp_move_ins(union mips_instruction *ip)
+{
+        /* addiu/daddiu sp,sp,-imm */
+        if (ip->i_format.rs != 29 || ip->i_format.rt != 29)
+                return 0;
+        if (ip->i_format.opcode == addiu_op || ip->i_format.opcode == daddiu_op)
+                return 1;
+        return 0;
+}
+
+/*
+ * Looks for specific instructions that mark the end of a function.
+ * This usually means we ran into the code area of the previous function.
+ */
+static inline int is_end_of_function_marker(union mips_instruction *ip)
+{
+        /* jr ra */
+        if (ip->r_format.func == jr_op && ip->r_format.rs == 31)
+                return 1;
+        /* lui gp */
+        if (ip->i_format.opcode == lui_op && ip->i_format.rt == 28)
+                return 1;
+        return 0;
+}
+
+/*
+ * TODO for userspace stack unwinding:
+ * - handle cases where the stack is adjusted inside a function
+ *     (generally doesn't happen)
+ * - find optimal value for max_instr_check
+ * - try to find a better way to handle leaf functions
+ */
+
+static inline int unwind_user_frame(struct stackframe *old_frame,
+                                    const unsigned int max_instr_check)
+{
+        struct stackframe new_frame = *old_frame;
+        off_t ra_offset = 0;
+        size_t stack_size = 0;
+        unsigned long addr;
+
+        if (old_frame->pc == 0 || old_frame->sp == 0 || old_frame->ra == 0)
+                return -9;
+
+        for (addr = new_frame.pc; (addr + max_instr_check > new_frame.pc)
+                && (!ra_offset || !stack_size); --addr) {
+                union mips_instruction ip;
+
+                if (get_mem(addr, (unsigned long *) &ip))
+                        return -11;
+
+                if (is_sp_move_ins(&ip)) {
+                        int stack_adjustment = ip.i_format.simmediate;
+                        if (stack_adjustment > 0)
+                                /* This marks the end of the previous function,
+                                   which means we overran. */
+                                break;
+                        stack_size = (unsigned long) stack_adjustment;
+                } else if (is_ra_save_ins(&ip)) {
+                        int ra_slot = ip.i_format.simmediate;
+                        if (ra_slot < 0)
+                                /* This shouldn't happen. */
+                                break;
+                        ra_offset = ra_slot;
+                } else if (is_end_of_function_marker(&ip))
+                        break;
+        }
+
+        if (!ra_offset || !stack_size)
+                goto done;
+
+        if (ra_offset) {
+                new_frame.ra = old_frame->sp + ra_offset;
+                if (get_mem(new_frame.ra, &(new_frame.ra)))
+                        return -13;
+        }
+
+        if (stack_size) {
+                new_frame.sp = old_frame->sp + stack_size;
+                if (get_mem(new_frame.sp, &(new_frame.sp)))
+                        return -14;
+        }
+
+        if (new_frame.sp > old_frame->sp)
+                return -2;
+
+done:
+        new_frame.pc = old_frame->ra;
+        *old_frame = new_frame;
+
+        return 0;
+}
+
+static inline void do_user_backtrace(unsigned long low_addr,
+                                     struct stackframe *frame,
+                                     unsigned int depth)
+{
+        const unsigned int max_instr_check = 512;
+        const unsigned long high_addr = low_addr + THREAD_SIZE;
+
+        while (depth-- && !unwind_user_frame(frame, max_instr_check)) {
+                oprofile_add_trace(frame->ra);
+                if (frame->sp < low_addr || frame->sp > high_addr)
+                        break;
+        }
+}
+
+#ifndef CONFIG_KALLSYMS
+static inline void do_kernel_backtrace(unsigned long low_addr,
+                                       struct stackframe *frame,
+                                       unsigned int depth) { }
+#else
+static inline void do_kernel_backtrace(unsigned long low_addr,
+                                       struct stackframe *frame,
+                                       unsigned int depth)
+{
+        while (depth-- && frame->pc) {
+                frame->pc = unwind_stack_by_address(low_addr,
+                                                    &(frame->sp),
+                                                    frame->pc,
+                                                    &(frame->ra));
+                oprofile_add_trace(frame->ra);
+        }
+}
+#endif
+
+void notrace op_mips_backtrace(struct pt_regs *const regs, unsigned int depth)
+{
+        struct stackframe frame = { .sp = regs->regs[29],
+                                    .pc = regs->cp0_epc,
+                                    .ra = regs->regs[31] };
+        const int userspace = user_mode(regs);
+        const unsigned long low_addr = ALIGN(frame.sp, THREAD_SIZE);
+
+        if (userspace)
+                do_user_backtrace(low_addr, &frame, depth);
+        else
+                do_kernel_backtrace(low_addr, &frame, depth);
+}