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Linux/arch/s390/kernel/ftrace.c

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  1 /*
  2  * Dynamic function tracer architecture backend.
  3  *
  4  * Copyright IBM Corp. 2009
  5  *
  6  *   Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
  7  *              Martin Schwidefsky <schwidefsky@de.ibm.com>
  8  */
  9 
 10 #include <linux/hardirq.h>
 11 #include <linux/uaccess.h>
 12 #include <linux/ftrace.h>
 13 #include <linux/kernel.h>
 14 #include <linux/types.h>
 15 #include <linux/kprobes.h>
 16 #include <trace/syscall.h>
 17 #include <asm/asm-offsets.h>
 18 #include "entry.h"
 19 
 20 #ifdef CONFIG_DYNAMIC_FTRACE
 21 
 22 void ftrace_disable_code(void);
 23 void ftrace_enable_insn(void);
 24 
 25 #ifdef CONFIG_64BIT
 26 /*
 27  * The 64-bit mcount code looks like this:
 28  *      stg     %r14,8(%r15)            # offset 0
 29  * >    larl    %r1,<&counter>          # offset 6
 30  * >    brasl   %r14,_mcount            # offset 12
 31  *      lg      %r14,8(%r15)            # offset 18
 32  * Total length is 24 bytes. The middle two instructions of the mcount
 33  * block get overwritten by ftrace_make_nop / ftrace_make_call.
 34  * The 64-bit enabled ftrace code block looks like this:
 35  *      stg     %r14,8(%r15)            # offset 0
 36  * >    lg      %r1,__LC_FTRACE_FUNC    # offset 6
 37  * >    lgr     %r0,%r0                 # offset 12
 38  * >    basr    %r14,%r1                # offset 16
 39  *      lg      %r14,8(%15)             # offset 18
 40  * The return points of the mcount/ftrace function have the same offset 18.
 41  * The 64-bit disable ftrace code block looks like this:
 42  *      stg     %r14,8(%r15)            # offset 0
 43  * >    jg      .+18                    # offset 6
 44  * >    lgr     %r0,%r0                 # offset 12
 45  * >    basr    %r14,%r1                # offset 16
 46  *      lg      %r14,8(%15)             # offset 18
 47  * The jg instruction branches to offset 24 to skip as many instructions
 48  * as possible.
 49  */
 50 asm(
 51         "       .align  4\n"
 52         "ftrace_disable_code:\n"
 53         "       jg      0f\n"
 54         "       lgr     %r0,%r0\n"
 55         "       basr    %r14,%r1\n"
 56         "0:\n"
 57         "       .align  4\n"
 58         "ftrace_enable_insn:\n"
 59         "       lg      %r1,"__stringify(__LC_FTRACE_FUNC)"\n");
 60 
 61 #define FTRACE_INSN_SIZE        6
 62 
 63 #else /* CONFIG_64BIT */
 64 /*
 65  * The 31-bit mcount code looks like this:
 66  *      st      %r14,4(%r15)            # offset 0
 67  * >    bras    %r1,0f                  # offset 4
 68  * >    .long   _mcount                 # offset 8
 69  * >    .long   <&counter>              # offset 12
 70  * > 0: l       %r14,0(%r1)             # offset 16
 71  * >    l       %r1,4(%r1)              # offset 20
 72  *      basr    %r14,%r14               # offset 24
 73  *      l       %r14,4(%r15)            # offset 26
 74  * Total length is 30 bytes. The twenty bytes starting from offset 4
 75  * to offset 24 get overwritten by ftrace_make_nop / ftrace_make_call.
 76  * The 31-bit enabled ftrace code block looks like this:
 77  *      st      %r14,4(%r15)            # offset 0
 78  * >    l       %r14,__LC_FTRACE_FUNC   # offset 4
 79  * >    j       0f                      # offset 8
 80  * >    .fill   12,1,0x07               # offset 12
 81  *   0: basr    %r14,%r14               # offset 24
 82  *      l       %r14,4(%r14)            # offset 26
 83  * The return points of the mcount/ftrace function have the same offset 26.
 84  * The 31-bit disabled ftrace code block looks like this:
 85  *      st      %r14,4(%r15)            # offset 0
 86  * >    j       .+26                    # offset 4
 87  * >    j       0f                      # offset 8
 88  * >    .fill   12,1,0x07               # offset 12
 89  *   0: basr    %r14,%r14               # offset 24
 90  *      l       %r14,4(%r14)            # offset 26
 91  * The j instruction branches to offset 30 to skip as many instructions
 92  * as possible.
 93  */
 94 asm(
 95         "       .align  4\n"
 96         "ftrace_disable_code:\n"
 97         "       j       1f\n"
 98         "       j       0f\n"
 99         "       .fill   12,1,0x07\n"
100         "0:     basr    %r14,%r14\n"
101         "1:\n"
102         "       .align  4\n"
103         "ftrace_enable_insn:\n"
104         "       l       %r14,"__stringify(__LC_FTRACE_FUNC)"\n");
105 
106 #define FTRACE_INSN_SIZE        4
107 
108 #endif /* CONFIG_64BIT */
109 
110 
111 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
112                     unsigned long addr)
113 {
114         if (probe_kernel_write((void *) rec->ip, ftrace_disable_code,
115                                MCOUNT_INSN_SIZE))
116                 return -EPERM;
117         return 0;
118 }
119 
120 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
121 {
122         if (probe_kernel_write((void *) rec->ip, ftrace_enable_insn,
123                                FTRACE_INSN_SIZE))
124                 return -EPERM;
125         return 0;
126 }
127 
128 int ftrace_update_ftrace_func(ftrace_func_t func)
129 {
130         return 0;
131 }
132 
133 int __init ftrace_dyn_arch_init(void *data)
134 {
135         *(unsigned long *) data = 0;
136         return 0;
137 }
138 
139 #endif /* CONFIG_DYNAMIC_FTRACE */
140 
141 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
142 /*
143  * Hook the return address and push it in the stack of return addresses
144  * in current thread info.
145  */
146 unsigned long __kprobes prepare_ftrace_return(unsigned long parent,
147                                               unsigned long ip)
148 {
149         struct ftrace_graph_ent trace;
150 
151         if (unlikely(atomic_read(&current->tracing_graph_pause)))
152                 goto out;
153         ip = (ip & PSW_ADDR_INSN) - MCOUNT_INSN_SIZE;
154         trace.func = ip;
155         trace.depth = current->curr_ret_stack + 1;
156         /* Only trace if the calling function expects to. */
157         if (!ftrace_graph_entry(&trace))
158                 goto out;
159         if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY)
160                 goto out;
161         parent = (unsigned long) return_to_handler;
162 out:
163         return parent;
164 }
165 
166 #ifdef CONFIG_DYNAMIC_FTRACE
167 /*
168  * Patch the kernel code at ftrace_graph_caller location. The instruction
169  * there is branch relative and save to prepare_ftrace_return. To disable
170  * the call to prepare_ftrace_return we patch the bras offset to point
171  * directly after the instructions. To enable the call we calculate
172  * the original offset to prepare_ftrace_return and put it back.
173  */
174 int ftrace_enable_ftrace_graph_caller(void)
175 {
176         unsigned short offset;
177 
178         offset = ((void *) prepare_ftrace_return -
179                   (void *) ftrace_graph_caller) / 2;
180         return probe_kernel_write((void *) ftrace_graph_caller + 2,
181                                   &offset, sizeof(offset));
182 }
183 
184 int ftrace_disable_ftrace_graph_caller(void)
185 {
186         static unsigned short offset = 0x0002;
187 
188         return probe_kernel_write((void *) ftrace_graph_caller + 2,
189                                   &offset, sizeof(offset));
190 }
191 
192 #endif /* CONFIG_DYNAMIC_FTRACE */
193 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
194 

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