arch/s390/kernel/ftrace.c

   1 /*
   2  * Dynamic function tracer architecture backend.
   3  *
   4  * Copyright IBM Corp. 2009,2014
   5  *
   6  *   Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
   7  *              Martin Schwidefsky <schwidefsky@de.ibm.com>
   8  */
   9
  10 #include <linux/moduleloader.h>
  11 #include <linux/hardirq.h>
  12 #include <linux/uaccess.h>
  13 #include <linux/ftrace.h>
  14 #include <linux/kernel.h>
  15 #include <linux/types.h>
  16 #include <linux/kprobes.h>
  17 #include <trace/syscall.h>
  18 #include <asm/asm-offsets.h>
  19 #include <asm/cacheflush.h>
  20 #include "entry.h"
  21
  22 /*
  23  * The mcount code looks like this:
  24  *      stg     %r14,8(%r15)            # offset 0
  25  *      larl    %r1,<&counter>          # offset 6
  26  *      brasl   %r14,_mcount            # offset 12
  27  *      lg      %r14,8(%r15)            # offset 18
  28  * Total length is 24 bytes. Only the first instruction will be patched
  29  * by ftrace_make_call / ftrace_make_nop.
  30  * The enabled ftrace code block looks like this:
  31  * >    brasl   %r0,ftrace_caller       # offset 0
  32  *      larl    %r1,<&counter>          # offset 6
  33  *      brasl   %r14,_mcount            # offset 12
  34  *      lg      %r14,8(%r15)            # offset 18
  35  * The ftrace function gets called with a non-standard C function call ABI
  36  * where r0 contains the return address. It is also expected that the called
  37  * function only clobbers r0 and r1, but restores r2-r15.
  38  * For module code we can't directly jump to ftrace caller, but need a
  39  * trampoline (ftrace_plt), which clobbers also r1.
  40  * The return point of the ftrace function has offset 24, so execution
  41  * continues behind the mcount block.
  42  * The disabled ftrace code block looks like this:
  43  * >    jg      .+24                    # offset 0
  44  *      larl    %r1,<&counter>          # offset 6
  45  *      brasl   %r14,_mcount            # offset 12
  46  *      lg      %r14,8(%r15)            # offset 18
  47  * The jg instruction branches to offset 24 to skip as many instructions
  48  * as possible.
  49  * In case we use gcc's hotpatch feature the original and also the disabled
  50  * function prologue contains only a single six byte instruction and looks
  51  * like this:
  52  * >    brcl    0,0                     # offset 0
  53  * To enable ftrace the code gets patched like above and afterwards looks
  54  * like this:
  55  * >    brasl   %r0,ftrace_caller       # offset 0
  56  */
  57
  58 unsigned long ftrace_plt;
  59
  60 static inline void ftrace_generate_orig_insn(struct ftrace_insn *insn)
  61 {
  62 #ifdef CC_USING_HOTPATCH
  63         /* brcl 0,0 */
  64         insn->opc = 0xc004;
  65         insn->disp = 0;
  66 #else
  67         /* stg r14,8(r15) */
  68         insn->opc = 0xe3e0;
  69         insn->disp = 0xf0080024;
  70 #endif
  71 }
  72
  73 static inline int is_kprobe_on_ftrace(struct ftrace_insn *insn)
  74 {
  75 #ifdef CONFIG_KPROBES
  76         if (insn->opc == BREAKPOINT_INSTRUCTION)
  77                 return 1;
  78 #endif
  79         return 0;
  80 }
  81
  82 static inline void ftrace_generate_kprobe_nop_insn(struct ftrace_insn *insn)
  83 {
  84 #ifdef CONFIG_KPROBES
  85         insn->opc = BREAKPOINT_INSTRUCTION;
  86         insn->disp = KPROBE_ON_FTRACE_NOP;
  87 #endif
  88 }
  89
  90 static inline void ftrace_generate_kprobe_call_insn(struct ftrace_insn *insn)
  91 {
  92 #ifdef CONFIG_KPROBES
  93         insn->opc = BREAKPOINT_INSTRUCTION;
  94         insn->disp = KPROBE_ON_FTRACE_CALL;
  95 #endif
  96 }
  97
  98 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
  99                        unsigned long addr)
 100 {
 101         return 0;
 102 }
 103
 104 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 105                     unsigned long addr)
 106 {
 107         struct ftrace_insn orig, new, old;
 108
 109         if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
 110                 return -EFAULT;
 111         if (addr == MCOUNT_ADDR) {
 112                 /* Initial code replacement */
 113                 ftrace_generate_orig_insn(&orig);
 114                 ftrace_generate_nop_insn(&new);
 115         } else if (is_kprobe_on_ftrace(&old)) {
 116                 /*
 117                  * If we find a breakpoint instruction, a kprobe has been
 118                  * placed at the beginning of the function. We write the
 119                  * constant KPROBE_ON_FTRACE_NOP into the remaining four
 120                  * bytes of the original instruction so that the kprobes
 121                  * handler can execute a nop, if it reaches this breakpoint.
 122                  */
 123                 ftrace_generate_kprobe_call_insn(&orig);
 124                 ftrace_generate_kprobe_nop_insn(&new);
 125         } else {
 126                 /* Replace ftrace call with a nop. */
 127                 ftrace_generate_call_insn(&orig, rec->ip);
 128                 ftrace_generate_nop_insn(&new);
 129         }
 130         /* Verify that the to be replaced code matches what we expect. */
 131         if (memcmp(&orig, &old, sizeof(old)))
 132                 return -EINVAL;
 133         s390_kernel_write((void *) rec->ip, &new, sizeof(new));
 134         return 0;
 135 }
 136
 137 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 138 {
 139         struct ftrace_insn orig, new, old;
 140
 141         if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
 142                 return -EFAULT;
 143         if (is_kprobe_on_ftrace(&old)) {
 144                 /*
 145                  * If we find a breakpoint instruction, a kprobe has been
 146                  * placed at the beginning of the function. We write the
 147                  * constant KPROBE_ON_FTRACE_CALL into the remaining four
 148                  * bytes of the original instruction so that the kprobes
 149                  * handler can execute a brasl if it reaches this breakpoint.
 150                  */
 151                 ftrace_generate_kprobe_nop_insn(&orig);
 152                 ftrace_generate_kprobe_call_insn(&new);
 153         } else {
 154                 /* Replace nop with an ftrace call. */
 155                 ftrace_generate_nop_insn(&orig);
 156                 ftrace_generate_call_insn(&new, rec->ip);
 157         }
 158         /* Verify that the to be replaced code matches what we expect. */
 159         if (memcmp(&orig, &old, sizeof(old)))
 160                 return -EINVAL;
 161         s390_kernel_write((void *) rec->ip, &new, sizeof(new));
 162         return 0;
 163 }
 164
 165 int ftrace_update_ftrace_func(ftrace_func_t func)
 166 {
 167         return 0;
 168 }
 169
 170 int __init ftrace_dyn_arch_init(void)
 171 {
 172         return 0;
 173 }
 174
 175 static int __init ftrace_plt_init(void)
 176 {
 177         unsigned int *ip;
 178
 179         ftrace_plt = (unsigned long) module_alloc(PAGE_SIZE);
 180         if (!ftrace_plt)
 181                 panic("cannot allocate ftrace plt\n");
 182         ip = (unsigned int *) ftrace_plt;
 183         ip[0] = 0x0d10e310; /* basr 1,0; lg 1,10(1); br 1 */
 184         ip[1] = 0x100a0004;
 185         ip[2] = 0x07f10000;
 186         ip[3] = FTRACE_ADDR >> 32;
 187         ip[4] = FTRACE_ADDR & 0xffffffff;
 188         set_memory_ro(ftrace_plt, 1);
 189         return 0;
 190 }
 191 device_initcall(ftrace_plt_init);
 192
 193 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 194 /*
 195  * Hook the return address and push it in the stack of return addresses
 196  * in current thread info.
 197  */
 198 unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip)
 199 {
 200         struct ftrace_graph_ent trace;
 201
 202         if (unlikely(ftrace_graph_is_dead()))
 203                 goto out;
 204         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 205                 goto out;
 206         ip -= MCOUNT_INSN_SIZE;
 207         trace.func = ip;
 208         trace.depth = current->curr_ret_stack + 1;
 209         /* Only trace if the calling function expects to. */
 210         if (!ftrace_graph_entry(&trace))
 211                 goto out;
 212         if (ftrace_push_return_trace(parent, ip, &trace.depth, 0,
 213                                      NULL) == -EBUSY)
 214                 goto out;
 215         parent = (unsigned long) return_to_handler;
 216 out:
 217         return parent;
 218 }
 219 NOKPROBE_SYMBOL(prepare_ftrace_return);
 220
 221 /*
 222  * Patch the kernel code at ftrace_graph_caller location. The instruction
 223  * there is branch relative on condition. To enable the ftrace graph code
 224  * block, we simply patch the mask field of the instruction to zero and
 225  * turn the instruction into a nop.
 226  * To disable the ftrace graph code the mask field will be patched to
 227  * all ones, which turns the instruction into an unconditional branch.
 228  */
 229 int ftrace_enable_ftrace_graph_caller(void)
 230 {
 231         u8 op = 0x04; /* set mask field to zero */
 232
 233         s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
 234         return 0;
 235 }
 236
 237 int ftrace_disable_ftrace_graph_caller(void)
 238 {
 239         u8 op = 0xf4; /* set mask field to all ones */
 240
 241         s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
 242         return 0;
 243 }
 244
 245 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */